syntax: new 'assert else' statement
[nit.git] / src / syntax / typing.nit
index ee2eb0a..0201f2d 100644 (file)
@@ -19,14 +19,15 @@ package typing
 
 import syntax_base
 import escape
+import control_flow
 
 redef class MMSrcModule
        # Walk trough the module and type statments and expressions
        # Require than supermodules are processed
-       meth do_typing(tc: ToolContext)
+       fun do_typing(tc: ToolContext)
        do
                var tv = new TypingVisitor(tc, self)
-               tv.visit(node)
+               tv.enter_visit(node)
        end
 end
 
@@ -37,44 +38,55 @@ end
 # * Check type conformance
 private class TypingVisitor
 special AbsSyntaxVisitor
-       redef meth visit(n)
+       redef fun visit(n)
        do
                if n != null then n.accept_typing(self)
        end
 
        # Current knowledge about variables names and types
-       readable writable attr _variable_ctx: VariableContext
+       fun variable_ctx: VariableContext do return _variable_ctx.as(not null)
+       writable var _variable_ctx: nullable VariableContext
+
+       # Non-bypassable knowledge about variables names and types
+       fun base_variable_ctx: VariableContext do return _base_variable_ctx.as(not null)
+       writable var _base_variable_ctx: nullable VariableContext
 
        # Current knowledge about escapable blocks
-       readable writable attr _escapable_ctx: EscapableContext = new EscapableContext(self)
+       readable writable var _escapable_ctx: EscapableContext = new EscapableContext(self)
 
        # The current reciever
-       readable writable attr _self_var: ParamVariable
+       fun self_var: ParamVariable do return _self_var.as(not null)
+       writable var _self_var: nullable ParamVariable
 
        # Block of the current method
-       readable writable attr _top_block: PExpr
+       readable writable var _top_block: nullable AExpr
 
        # List of explicit invocation of constructors of super-classes
-       readable writable attr _explicit_super_init_calls: Array[MMMethod]
+       readable writable var _explicit_super_init_calls: nullable Array[MMMethod]
 
        # Is a other constructor of the same class invoked
-       readable writable attr _explicit_other_init_call: Bool
+       readable writable var _explicit_other_init_call: Bool = false
 
        # Make the if_true_variable_ctx of the expression effective
-       private meth use_if_true_variable_ctx(e: PExpr)
+       private fun use_if_true_variable_ctx(e: AExpr)
        do
                var ctx = e.if_true_variable_ctx
-               if ctx != null then
-                       variable_ctx = ctx
-               end
+               if ctx != null then variable_ctx = ctx
+       end
+
+       # Make the if_false_variable_ctx of the expression effective
+       private fun use_if_false_variable_ctx(e: AExpr)
+       do
+               var ctx = e.if_false_variable_ctx
+               if ctx != null then variable_ctx = ctx
        end
 
        # Number of nested once
-       readable writable attr _once_count: Int = 0
+       readable writable var _once_count: Int = 0
 
        init(tc, module) do super
 
-       private meth get_default_constructor_for(n: PNode, c: MMLocalClass, prop: MMSrcMethod): MMMethod
+       private fun get_default_constructor_for(n: ANode, c: MMLocalClass, prop: MMSrcMethod): nullable MMMethod
        do
                var v = self
                #var prop = v.local_property
@@ -88,7 +100,7 @@ special AbsSyntaxVisitor
                        var gps = gp.signature_for(c.get_type)
                        assert gp isa MMSrcMethod
                        var garity = gps.arity
-                       if prop != null and gp.name == prop.name then
+                       if gp.name == prop.name then
                                if garity == 0 or (parity == garity and prop.signature < gps) then
                                        return gp
                                else
@@ -124,247 +136,61 @@ special AbsSyntaxVisitor
        end
 end
 
-# Associate symbols to variable and variables to type
-# Can be nested
-abstract class VariableContext
-       # Look for the variable from its name
-       # Return null if nothing found
-       meth [](s: Symbol): Variable
-       do
-               if _dico.has_key(s) then
-                       return _dico[s]
-               else
-                       return null
-               end
-       end
-
-       # Register a new variable with its name
-       meth add(v: Variable)
-       do
-               _dico[v.name] = v
-               _all_variables.add(v)
-       end
-
-       meth mark_is_set(v: Variable)
-       do
-               _set_variables.add(v)
-       end
-
-       meth check_is_set(n: PNode, v: Variable)
-       do
-               if v.must_be_set and not is_set(v) then
-                       _visitor.error(n, "Error: variable '{v}' is possibly unset.")
-                       var x = self
-                       while true do
-                               print "  {x.node.locate}: {x._set_variables.join(", ")} ; {x._dico.join(", ")}"
-                               var x0 = x
-                               if x0 isa SubVariableContext then
-                                       x = x0.prev
-                               else
-                                       break
-                               end
-                       end
-               end
-       end
-
-       # The effective static type of a given variable
-       # May be different from the declaration static type
-       meth stype(v: Variable): MMType
-       do
-               return v.stype
-       end
-
-       # Variables by name (in the current context only)
-       attr _dico: Map[Symbol, Variable]
-
-       # All variables in all contextes
-       attr _all_variables: Set[Variable]
-
-       # Build a new VariableContext
-       meth sub(node: PNode): SubVariableContext
-       do
-               return new SubVariableContext.with_prev(self, node)
-       end
-
-       # Build a nested VariableContext with new variable information
-       meth sub_with(node: PNode, v: Variable, t: MMType): SubVariableContext
-       do
-               return new CastVariableContext.with_prev(self, node, v, t)
-       end
-
-       # The visitor of the context (used to display error)
-       attr _visitor: AbsSyntaxVisitor
-
-       # The syntax node that introduced the context
-       readable attr _node: PNode
-
-       init(visitor: AbsSyntaxVisitor, node: PNode)
-       do
-               _visitor = visitor
-               _node = node
-               _dico = new HashMap[Symbol, Variable]
-       end
-
-       # Is a control flow break met? (return, break, continue)
-       readable writable attr _unreash: Bool = false
-
-       # Is a control flow already broken?
-       # Used to avoid repeating the same error message
-       readable writable attr _already_unreash: Bool = false
-
-       # Set of variable that are set (assigned)
-       readable attr _set_variables: HashSet[Variable] = new HashSet[Variable]
-
-       # Is a variable set?
-       meth is_set(v: Variable): Bool
-       do
-               return _set_variables.has(v)
-       end
-
-       # Merge back one flow context information
-       meth merge(ctx: VariableContext)
-       do
-               if ctx.unreash then
-                       unreash = true
-                       if ctx.already_unreash then already_unreash = true
-                       return
-               end
-               for v in _all_variables do
-                       if not is_set(v) and ctx.is_set(v) then
-                               mark_is_set(v)
-                       end
-               end
-       end
-
-       # Merge back two alternative flow context informations
-       meth merge2(ctx1, ctx2: VariableContext)
-       do
-               if ctx1.unreash then
-                       merge(ctx2)
-               else if ctx2.unreash then
-                       merge(ctx1)
-               end
-               for v in _all_variables do
-                       if not is_set(v) and ctx1.is_set(v) and ctx2.is_set(v) then
-                               mark_is_set(v)
-                       end
-               end
-       end
-end
-
-class RootVariableContext
-special VariableContext
-       init(visitor: AbsSyntaxVisitor, node: PNode)
-       do
-               super(visitor, node)
-               _all_variables = new HashSet[Variable]
-       end
-end
-
-class SubVariableContext
-special VariableContext
-       readable attr _prev: VariableContext
-
-       redef meth [](s)
-       do
-               if _dico.has_key(s) then
-                       return _dico[s]
-               else
-                       return prev[s]
-               end
-       end
-
-       redef meth stype(v)
-       do
-               return prev.stype(v)
-       end
-
-       init with_prev(p: VariableContext, node: PNode)
-       do
-               init(p._visitor, node)
-               _prev = p
-               _all_variables = p._all_variables
-       end
-
-       redef meth is_set(v)
-       do
-               return _set_variables.has(v) or _prev.is_set(v)
-       end
-end
-
-class CastVariableContext
-special SubVariableContext
-       attr _variable: Variable
-       attr _var_type: MMType
-
-       redef meth stype(v)
-       do
-               if _variable == v then
-                       return _var_type
-               end
-               return prev.stype(v)
-       end
-
-       init with_prev(p: VariableContext, node: PNode, v: Variable, t: MMType)
-       do
-               super(p, node)
-               _variable = v
-               _var_type =t
-       end
-end
-
-redef class Variable
-       # Is the variable must be set before being used ?
-       meth must_be_set: Bool do return false
-end
-
-redef class VarVariable
-       redef meth must_be_set do return true
-end
-
 
 ###############################################################################
 
-redef class PNode
-       private meth accept_typing(v: TypingVisitor) 
+redef class ANode
+       private fun accept_typing(v: TypingVisitor) 
        do
                accept_abs_syntax_visitor(v)
                after_typing(v)
        end
-       private meth after_typing(v: TypingVisitor) do end
+       private fun after_typing(v: TypingVisitor) do end
 end
 
-redef class PClassdef
-       redef meth accept_typing(v)
+redef class AClassdef
+       redef fun accept_typing(v)
        do
+               v.variable_ctx = new RootVariableContext(v, self)
+               v.base_variable_ctx = v.variable_ctx
                v.self_var = new ParamVariable("self".to_symbol, self)
                v.self_var.stype = local_class.get_type
                super
        end
 end
 
+redef class APropdef
+       redef fun self_var do return _self_var.as(not null)
+       var _self_var: nullable ParamVariable
+end
+
 redef class AAttrPropdef
-       redef meth accept_typing(v)
+       redef fun accept_typing(v)
        do
+               var old_var_ctx = v.variable_ctx
+               v.variable_ctx = old_var_ctx.sub(self)
+               _self_var = v.self_var
                super
                if n_expr != null then
-                       v.check_conform_expr(n_expr, prop.signature.return_type)
+                       v.check_conform_expr(n_expr.as(not null), prop.signature.return_type.as(not null))
                end
+               v.variable_ctx = old_var_ctx
        end
 end
 
 redef class AMethPropdef
-       redef readable attr _self_var: ParamVariable
-       redef meth accept_typing(v)
+       redef fun accept_typing(v)
        do
-               v.variable_ctx = new RootVariableContext(v, self)
+               var old_var_ctx = v.variable_ctx
+               v.variable_ctx = old_var_ctx.sub(self)
                _self_var = v.self_var
                super
+               v.variable_ctx = old_var_ctx
        end
 end
 
 redef class AConcreteMethPropdef
-       redef meth accept_typing(v)
+       redef fun after_typing(v)
        do
                super
                if v.variable_ctx.unreash == false and method.signature.return_type != null then
@@ -374,21 +200,24 @@ redef class AConcreteMethPropdef
 end
 
 redef class AConcreteInitPropdef
-       readable attr _super_init_calls: Array[MMMethod] = new Array[MMMethod]
-       readable attr _explicit_super_init_calls: Array[MMMethod] = new Array[MMMethod]
-       redef meth accept_typing(v)
+       redef fun accept_typing(v)
        do
                v.top_block = n_block
                v.explicit_super_init_calls = explicit_super_init_calls
                v.explicit_other_init_call = false
                super
+       end
+
+       redef fun after_typing(v)
+       do
+               super
                if v.explicit_other_init_call or method.global.intro != method then
                        # TODO: something?
                else 
                        var i = 0
                        var l = explicit_super_init_calls.length
-                       var cur_m: MMMethod = null
-                       var cur_c: MMLocalClass = null
+                       var cur_m: nullable MMMethod = null
+                       var cur_c: nullable MMLocalClass = null
                        if i < l then
                                cur_m = explicit_super_init_calls[i]
                                cur_c = cur_m.global.intro.local_class.for_module(v.module)
@@ -400,7 +229,7 @@ redef class AConcreteInitPropdef
                                        j += 1
                                else if cur_c != null and (c.cshe <= cur_c or cur_c.global.is_mixin) then
                                        if c == cur_c then j += 1
-                                       super_init_calls.add(cur_m)
+                                       super_init_calls.add(cur_m.as(not null))
                                        i += 1
                                        if i < l then
                                                cur_m = explicit_super_init_calls[i]
@@ -421,30 +250,30 @@ redef class AConcreteInitPropdef
        end
 end
 
-redef class PParam
-       redef meth after_typing(v)
+redef class AParam
+       redef fun after_typing(v)
        do
-               # TODO: why the test?
-               if v.variable_ctx != null then
-                       v.variable_ctx.add(variable)
-               end
+               v.variable_ctx.add(variable)
        end
 end
 
 redef class AClosureDecl
        # The corresponding escapable object
-       readable attr _escapable: EscapableBlock
+       readable var _escapable: nullable EscapableBlock
 
-       redef meth accept_typing(v)
+       redef fun accept_typing(v)
        do
                # Register the closure for ClosureCallExpr
                v.variable_ctx.add(variable)
 
                var old_var_ctx = v.variable_ctx
+               var old_base_var_ctx = v.base_variable_ctx
+               v.base_variable_ctx = v.variable_ctx
                v.variable_ctx = v.variable_ctx.sub(self)
 
-               _escapable = new EscapableClosure(self, variable.closure, null)
-               v.escapable_ctx.push(_escapable)
+               var escapable = new EscapableClosure(self, variable.closure, null)
+               _escapable = escapable
+               v.escapable_ctx.push(escapable, null)
 
                super
 
@@ -460,63 +289,80 @@ redef class AClosureDecl
 
                old_var_ctx.merge(v.variable_ctx)
                v.variable_ctx = old_var_ctx
+               v.base_variable_ctx = old_base_var_ctx
                v.escapable_ctx.pop
        end
 end
 
-redef class PType
-       readable attr _stype: MMType
-       redef meth after_typing(v)
+redef class AType
+       redef fun stype: MMType do return _stype.as(not null)
+       redef fun is_typed: Bool do return _stype != null
+       var _stype: nullable MMType
+
+       redef fun after_typing(v)
        do
                _stype = get_stype(v)
        end
 end
 
-redef class PExpr
-       redef readable attr _is_typed: Bool = false
-       redef meth is_statement: Bool do return _stype == null
-       redef meth stype
+redef class AExpr
+       redef readable var _is_typed: Bool = false
+       redef fun is_statement: Bool do return _stype == null
+       redef fun stype
        do
                if not is_typed then
-                       print "{locate}: not is_typed"
+                       print "{location}: not is_typed"
                        abort
                end
                if is_statement then
-                       print "{locate}: is_statement"
+                       print "{location}: is_statement"
                        abort
                end
-               return _stype
+               return _stype.as(not null)
+       end
+       var _stype: nullable MMType
+
+       redef fun after_typing(v)
+       do
+               # Default behavior is to be happy
+               _is_typed = true
        end
-       attr _stype: MMType
 
        # Is the expression the implicit receiver
-       meth is_implicit_self: Bool do return false
+       fun is_implicit_self: Bool do return false
 
        # Is the expression the current receiver (implicit or explicit)
-       meth is_self: Bool do return false
+       fun is_self: Bool do return false
 
        # The variable accessed is any
-       meth its_variable: Variable do return null
+       fun its_variable: nullable Variable do return null
 
        # The variable type information if current boolean expression is true
-       readable private attr _if_true_variable_ctx: VariableContext
+       readable private var _if_true_variable_ctx: nullable VariableContext
+
+       # The variable type information if current boolean expression is false
+       readable private var _if_false_variable_ctx: nullable VariableContext
 end
 
 redef class AVardeclExpr
-       redef meth after_typing(v)
+       var _variable: nullable VarVariable
+       redef fun variable do return _variable.as(not null)
+
+       redef fun after_typing(v)
        do
-               var va = new VarVariable(n_id.to_symbol, self)
-               variable = va
+               var va = new VarVariable(n_id.to_symbol, n_id)
+               _variable = va
                v.variable_ctx.add(va)
                if n_expr != null then v.variable_ctx.mark_is_set(va)
 
                if n_type != null then
+                       if not n_type.is_typed then return
                        va.stype = n_type.stype
                        if n_expr != null then
-                               v.check_conform_expr(n_expr, va.stype)
+                               v.check_conform_expr(n_expr.as(not null), va.stype)
                        end
                else
-                       if not v.check_expr(n_expr) then return
+                       if not v.check_expr(n_expr.as(not null)) then return
                        va.stype = n_expr.stype
                end
                _is_typed = true
@@ -524,7 +370,7 @@ redef class AVardeclExpr
 end
 
 redef class ABlockExpr
-       redef meth accept_typing(v)
+       redef fun accept_typing(v)
        do
                var old_var_ctx = v.variable_ctx
                v.variable_ctx = v.variable_ctx.sub(self)
@@ -534,7 +380,7 @@ redef class ABlockExpr
                                v.variable_ctx.already_unreash = true
                                v.warning(e, "Warning: unreachable statement.")
                        end
-                       v.visit(e)
+                       v.enter_visit(e)
                end
 
                old_var_ctx.merge(v.variable_ctx)
@@ -544,30 +390,31 @@ redef class ABlockExpr
 end
 
 redef class AReturnExpr
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                v.variable_ctx.unreash = true
                var t = v.local_property.signature.return_type
-               if n_expr == null and t != null then
+               var e = n_expr
+               if e == null and t != null then
                        v.error(self, "Error: Return without value in a function.")
-               else if n_expr != null and t == null then
+               else if e != null and t == null then
                        v.error(self, "Error: Return with value in a procedure.")
-               else if n_expr != null and t != null then
-                       v.check_conform_expr(n_expr, t)
+               else if e != null and t != null then
+                       v.check_conform_expr(e, t)
                end
                _is_typed = true
        end
 end
 
 redef class AContinueExpr
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                v.variable_ctx.unreash = true
                var esc = compute_escapable_block(v.escapable_ctx)
                if esc == null then return
 
                if esc.is_break_block then
-                       v.error(self, "Error: 'continue' forbiden in break blocks.")
+                       v.error(self, "Error: cannot 'continue', only 'break'.")
                        return
                end
 
@@ -577,14 +424,14 @@ redef class AContinueExpr
                else if n_expr != null and t == null then
                        v.error(self, "Error: continue without value required in this block.")
                else if n_expr != null and t != null then
-                       v.check_conform_expr(n_expr, t)
+                       v.check_conform_expr(n_expr.as(not null), t)
                end
                _is_typed = true
        end
 end
 
 redef class ABreakExpr
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                v.variable_ctx.unreash = true
                var esc = compute_escapable_block(v.escapable_ctx)
@@ -597,138 +444,210 @@ redef class ABreakExpr
                        v.error(self, "Error: break without value required in this block.")
                else if n_expr != null and bl != null then
                        # Typing check can only be done later
-                       bl.add(n_expr)
+                       bl.add(n_expr.as(not null))
                end
                _is_typed = true
        end
 end
 
 redef class AAbortExpr
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                v.variable_ctx.unreash = true
+               _is_typed = true
+       end
+end
+
+redef class ADoExpr
+       # The corresponding escapable block
+       readable var _escapable: nullable EscapableBlock
+
+       redef fun accept_typing(v)
+       do
+               var escapable = new BreakOnlyEscapableBlock(self)
+               _escapable = escapable
+               v.escapable_ctx.push(escapable, n_label)
+
+               super
+
+               v.escapable_ctx.pop
+               _is_typed = true
        end
 end
 
 redef class AIfExpr
-       redef meth accept_typing(v)
+       redef fun accept_typing(v)
        do
                var old_var_ctx = v.variable_ctx
-               v.visit(n_expr)
+               v.enter_visit(n_expr)
                v.check_conform_expr(n_expr, v.type_bool)
 
+               # Prepare 'then' context
                v.use_if_true_variable_ctx(n_expr)
-               v.variable_ctx = v.variable_ctx.sub(n_then)
 
-               v.visit(n_then)
+               # Process the 'then'
+               if n_then != null then
+                       v.variable_ctx = v.variable_ctx.sub(n_then.as(not null))
+                       v.enter_visit(n_then)
+               end
 
-               if n_else == null then
-                       # Restore variable ctx since the 'then' block is optional
-                       v.variable_ctx = old_var_ctx
-               else
-                       # Remember what appened in the 'then'
-                       var then_var_ctx = v.variable_ctx
-                       # Reset to process the 'else'
-                       v.variable_ctx = old_var_ctx.sub(n_else)
-                       v.visit(n_else)
-                       # Merge then and else in the old control_flow
-                       old_var_ctx.merge2(then_var_ctx, v.variable_ctx)
-                       v.variable_ctx = old_var_ctx
+               # Remember what appened in the 'then'
+               var then_var_ctx = v.variable_ctx
+
+               # Prepare 'else' context
+               v.variable_ctx = old_var_ctx
+               v.use_if_false_variable_ctx(n_expr)
+
+               # Process the 'else'
+               if n_else != null then
+                       v.variable_ctx = v.variable_ctx.sub(n_else.as(not null))
+                       v.enter_visit(n_else)
                end
+
+               # Merge 'then' and 'else' contexts
+               old_var_ctx.merge2(then_var_ctx, v.variable_ctx, v.base_variable_ctx)
+               v.variable_ctx = old_var_ctx
                _is_typed = true
        end
 end
 
 redef class AWhileExpr
        # The corresponding escapable block
-       readable attr _escapable: EscapableBlock
+       readable var _escapable: nullable EscapableBlock
 
-       redef meth accept_typing(v)
+       redef fun accept_typing(v)
        do
-               _escapable = new EscapableBlock(self)
-               v.escapable_ctx.push(_escapable)
+               var escapable = new EscapableBlock(self)
+               _escapable = escapable
+               v.escapable_ctx.push(escapable, n_label)
                var old_var_ctx = v.variable_ctx
+               var old_base_var_ctx = v.base_variable_ctx
+               v.base_variable_ctx = v.variable_ctx
                v.variable_ctx = v.variable_ctx.sub(self)
 
-               super
-
+               # Process condition
+               v.enter_visit(n_expr)
                v.check_conform_expr(n_expr, v.type_bool)
+
+               # Prepare inside context (assert cond)
+               v.use_if_true_variable_ctx(n_expr)
+
+               # Process inside
+               if n_block != null then
+                       v.variable_ctx = v.variable_ctx.sub(n_block.as(not null))
+                       v.enter_visit(n_block)
+               end
+
+               v.variable_ctx = old_var_ctx
+               v.base_variable_ctx = old_base_var_ctx
+               v.escapable_ctx.pop
+               _is_typed = true
+       end
+end
+
+redef class ALoopExpr
+       # The corresponding escapable block
+       readable var _escapable: nullable EscapableBlock
+
+       redef fun accept_typing(v)
+       do
+               var escapable = new EscapableBlock(self)
+               _escapable = escapable
+               v.escapable_ctx.push(escapable, n_label)
+               var old_var_ctx = v.variable_ctx
+               var old_base_var_ctx = v.base_variable_ctx
+               v.base_variable_ctx = v.variable_ctx
+               v.variable_ctx = v.variable_ctx.sub(self)
+
+               # Process inside
+               if n_block != null then
+                       v.variable_ctx = v.variable_ctx.sub(n_block.as(not null))
+                       v.enter_visit(n_block)
+               end
+
                v.variable_ctx = old_var_ctx
+               v.base_variable_ctx = old_base_var_ctx
                v.escapable_ctx.pop
                _is_typed = true
        end
 end
 
 redef class AForExpr
+       var _variable: nullable AutoVariable
+       redef fun variable do return _variable.as(not null)
+
        # The corresponding escapable block
-       readable attr _escapable: EscapableBlock
+       readable var _escapable: nullable EscapableBlock
 
-       readable attr _meth_iterator: MMMethod
-       readable attr _meth_is_ok: MMMethod
-       readable attr _meth_item: MMMethod
-       readable attr _meth_next: MMMethod
-       redef meth accept_typing(v)
+       redef fun accept_typing(v)
        do
-               _escapable = new EscapableBlock(self)
-               v.escapable_ctx.push(_escapable)
+               var escapable = new EscapableBlock(self)
+               _escapable = escapable
+               v.escapable_ctx.push(escapable, n_label)
 
                var old_var_ctx = v.variable_ctx
+               var old_base_var_ctx = v.base_variable_ctx
+               v.base_variable_ctx = v.variable_ctx
                v.variable_ctx = v.variable_ctx.sub(self)
-               var va = new AutoVariable(n_id.to_symbol, self)
-               variable = va
+               var va = new AutoVariable(n_id.to_symbol, n_id)
+               _variable = va
                v.variable_ctx.add(va)
 
-               v.visit(n_expr)
+               # Process collection
+               v.enter_visit(n_expr)
 
                if not v.check_conform_expr(n_expr, v.type_collection) then return
                var expr_type = n_expr.stype
-               _meth_iterator = expr_type.local_class.select_method(once ("iterator".to_symbol))
-               if _meth_iterator == null then
-                       v.error(self, "Error: Collection MUST have an iterate method")
-                       return
-               end
-               var iter_type = _meth_iterator.signature_for(expr_type).return_type
-               _meth_is_ok = iter_type.local_class.select_method(once ("is_ok".to_symbol))
-               if _meth_is_ok == null then
-                       v.error(self, "Error: {iter_type} MUST have an is_ok method")
-                       return
-               end
-               _meth_item = iter_type.local_class.select_method(once ("item".to_symbol))
-               if _meth_item == null then
-                       v.error(self, "Error: {iter_type} MUST have an item method")
-                       return
-               end
-               _meth_next = iter_type.local_class.select_method(once ("next".to_symbol))
-               if _meth_next == null then
-                       v.error(self, "Error: {iter_type} MUST have a next method")
-                       return
-               end
-               var t = _meth_item.signature_for(iter_type).return_type
-               if not n_expr.is_self then t = t.not_for_self
-               va.stype = t
 
-               if n_block != null then v.visit(n_block)
+               # Get iterator
+               var meth_iterator = v.get_method(expr_type, once "iterator".to_symbol)
+               var iter_type = meth_iterator.signature_for(expr_type).return_type.as(not null)
+               var meth_item = v.get_method(iter_type, once ("item".to_symbol))
+               var va_stype = meth_item.signature_for(iter_type).return_type.as(not null)
+               if not n_expr.is_self then va_stype = va_stype.not_for_self
+               va.stype = va_stype
+
+               # Body evaluation
+               if n_block != null then v.enter_visit(n_block)
 
                # pop context
                v.variable_ctx = old_var_ctx
+               v.base_variable_ctx = old_base_var_ctx
                v.escapable_ctx.pop
                _is_typed = true
        end
 end
 
 redef class AAssertExpr
-       redef meth after_typing(v)
+       redef fun accept_typing(v)
        do
+               # Process condition
+               v.enter_visit(n_expr)
                v.check_conform_expr(n_expr, v.type_bool)
+
+               # Process optional 'else' part
+               if n_else != null then
+                       var old_var_ctx = v.variable_ctx
+                       v.use_if_false_variable_ctx(n_expr)
+                       v.enter_visit(n_else)
+                       v.variable_ctx = old_var_ctx
+               end
+
+               # Prepare outside
                v.use_if_true_variable_ctx(n_expr)
                _is_typed = true
        end
 end
 
+redef class AVarFormExpr
+       var _variable: nullable Variable
+       redef fun variable do return _variable.as(not null)
+end
+
 redef class AVarExpr
-       redef meth its_variable do return variable
+       redef fun its_variable do return variable
 
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                v.variable_ctx.check_is_set(self, variable)
                _stype = v.variable_ctx.stype(variable)
@@ -737,98 +656,131 @@ redef class AVarExpr
 end
 
 redef class AVarAssignExpr
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                v.variable_ctx.mark_is_set(variable)
                var t = v.variable_ctx.stype(variable)
-               v.check_conform_expr(n_value, t)
+
+               # Check the base type
+               var btype = v.base_variable_ctx.stype(variable)
+               if not v.check_conform_expr(n_value, btype) then return
+
+               # Always cast
+               v.variable_ctx.stype(variable) = n_value.stype
+
                _is_typed = true
        end
 end
 
 redef class AReassignFormExpr
-       # Compute and check method used through the reassigment operator 
-       private meth do_lvalue_typing(v: TypingVisitor, type_lvalue: MMType)
+       # Compute and check method used through the reassigment operator
+       # On success return the static type of the result of the reassigment operator
+       # Else display an error and return null
+       private fun do_rvalue_typing(v: TypingVisitor, type_lvalue: nullable MMType): nullable MMType
        do
                if type_lvalue == null then
-                       return
+                       return null
                end
                var name = n_assign_op.method_name
                var lc = type_lvalue.local_class
                if not lc.has_global_property_by_name(name) then
                        v.error(self, "Error: Method '{name}' doesn't exists in {type_lvalue}.")
-                       return
+                       return null
                end
                var prop = lc.select_method(name)
                prop.global.check_visibility(v, self, v.module, false)
                var psig = prop.signature_for(type_lvalue)
                _assign_method = prop
-               if not v.check_conform_expr(n_value, psig[0].not_for_self) then return
-               if not v.check_conform(self, psig.return_type.not_for_self, n_value.stype) then return
+               if not v.check_conform_expr(n_value, psig[0].not_for_self) then return null
+               return psig.return_type.not_for_self
        end
 
-       # Method used through the reassigment operator (once computed)
-       readable attr _assign_method: MMMethod
+       redef fun assign_method do return _assign_method.as(not null)
+       var _assign_method: nullable MMMethod
 end
 
 redef class AVarReassignExpr
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                v.variable_ctx.check_is_set(self, variable)
                v.variable_ctx.mark_is_set(variable)
                var t = v.variable_ctx.stype(variable)
-               do_lvalue_typing(v, t)
+               var t2 = do_rvalue_typing(v, t)
+               if t2 == null then return
+
+               # Check the base type
+               var btype = v.base_variable_ctx.stype(variable)
+               if not v.check_conform(n_value, t2, btype) then return
+
+               # Always cast
+               v.variable_ctx.stype(variable) = t2
+
                _is_typed = true
        end
 end
 
-redef class PAssignOp
-       meth method_name: Symbol is abstract
+redef class AAssignOp
+       fun method_name: Symbol is abstract
 end
 redef class APlusAssignOp
-       redef meth method_name do return once "+".to_symbol
+       redef fun method_name do return once "+".to_symbol
 end
 redef class AMinusAssignOp
-       redef meth method_name do return once "-".to_symbol
+       redef fun method_name do return once "-".to_symbol
 end
 
 redef class ASelfExpr
-       redef meth its_variable do return variable
+       var _variable: nullable ParamVariable
+       redef fun variable do return _variable.as(not null)
+
+       redef fun its_variable do return variable
 
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
-               variable = v.self_var
+               _variable = v.self_var
                _stype = v.variable_ctx.stype(variable)
                _is_typed = true
        end
 
-        redef meth is_self do return true
+        redef fun is_self do return true
 end
 
 redef class AImplicitSelfExpr
-        redef meth is_implicit_self do return true
+        redef fun is_implicit_self do return true
 end
 
 redef class AIfexprExpr
-       redef meth accept_typing(v)
+       redef fun accept_typing(v)
        do
                var old_var_ctx = v.variable_ctx
 
-               v.visit(n_expr)
+               # Process condition
+               v.enter_visit(n_expr)
+               v.check_conform_expr(n_expr, v.type_bool)
+
+               # Prepare 'then' context
                v.use_if_true_variable_ctx(n_expr)
-               v.visit(n_then)
+
+               # Process 'then'
+               v.enter_visit(n_then)
+
+               # Prepare 'else' context
                v.variable_ctx = old_var_ctx
-               v.visit(n_else)
+               v.use_if_false_variable_ctx(n_expr)
 
-               v.check_conform_expr(n_expr, v.type_bool)
+               # Process 'else'
+               v.enter_visit(n_else)
 
-               _stype = v.check_conform_multiexpr(null, [n_then, n_else])
-               _is_typed = _stype != null
+               var stype = v.check_conform_multiexpr(null, [n_then, n_else])
+               if stype == null then return
+
+               _stype = stype
+               _is_typed = true
        end
 end
 
 redef class ABoolExpr
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                _stype = v.type_bool
                _is_typed = true
@@ -836,25 +788,50 @@ redef class ABoolExpr
 end
 
 redef class AOrExpr
-       redef meth after_typing(v)
+       redef fun accept_typing(v)
        do
-               v.check_conform_expr(n_expr, v.type_bool)
-               v.check_conform_expr(n_expr2, v.type_bool)
-               _stype = v.type_bool
+               var old_var_ctx = v.variable_ctx
+               var stype = v.type_bool
+               _stype = stype
+
+               # Process left operand
+               v.enter_visit(n_expr)
+
+               # Prepare right operand context
+               v.use_if_false_variable_ctx(n_expr)
+
+               # Process right operand
+               v.enter_visit(n_expr2)
+               if n_expr2.if_false_variable_ctx != null then
+                       _if_false_variable_ctx = n_expr2.if_false_variable_ctx
+               else
+                       _if_false_variable_ctx = v.variable_ctx
+               end
+
+               v.variable_ctx = old_var_ctx
+
+               v.check_conform_expr(n_expr, stype)
+               v.check_conform_expr(n_expr2, stype)
+               _stype = stype
                _is_typed = true
        end
 end
 
 redef class AAndExpr
-       redef meth accept_typing(v)
+       redef fun accept_typing(v)
        do
                var old_var_ctx = v.variable_ctx
+               var stype = v.type_bool
+
+               # Process left operand
+               v.enter_visit(n_expr)
 
-               v.visit(n_expr)
+               # Prepare right operand context
                v.use_if_true_variable_ctx(n_expr)
 
-               v.visit(n_expr2)
-               if n_expr2.if_true_variable_ctx != null then 
+               # Process right operand
+               v.enter_visit(n_expr2)
+               if n_expr2.if_true_variable_ctx != null then
                        _if_true_variable_ctx = n_expr2.if_true_variable_ctx
                else
                        _if_true_variable_ctx = v.variable_ctx
@@ -862,24 +839,29 @@ redef class AAndExpr
 
                v.variable_ctx = old_var_ctx
 
-               v.check_conform_expr(n_expr, v.type_bool)
-               v.check_conform_expr(n_expr2, v.type_bool)
-               _stype = v.type_bool
+               v.check_conform_expr(n_expr, stype)
+               v.check_conform_expr(n_expr2, stype)
+               _stype = stype
                _is_typed = true
        end
 end
 
 redef class ANotExpr
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                v.check_conform_expr(n_expr, v.type_bool)
+
+               # Invert if_true/if_false information
+               _if_false_variable_ctx = n_expr._if_true_variable_ctx
+               _if_true_variable_ctx = n_expr._if_false_variable_ctx
+
                _stype = v.type_bool
                _is_typed = true
        end
 end
 
 redef class AIntExpr
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                _stype = v.type_int
                _is_typed = true
@@ -887,7 +869,7 @@ redef class AIntExpr
 end
 
 redef class AFloatExpr
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                _stype = v.type_float
                _is_typed = true
@@ -895,7 +877,7 @@ redef class AFloatExpr
 end
 
 redef class ACharExpr
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                _stype = v.type_char
                _is_typed = true
@@ -903,37 +885,28 @@ redef class ACharExpr
 end
 
 redef class AStringFormExpr
-       readable attr _meth_with_native: MMMethod
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                _stype = v.type_string
                _is_typed = true
-               _meth_with_native = _stype.local_class.select_method(once "with_native".to_symbol)
-               if _meth_with_native == null then v.error(self, "{_stype} MUST have a with_native method.")
        end
 end
 
 redef class ASuperstringExpr
-       readable attr _meth_with_capacity: MMMethod
-       readable attr _meth_add: MMMethod
-       readable attr _meth_to_s: MMMethod
-       readable attr _atype: MMType
-       redef meth after_typing(v)
-       do
-               _stype = v.type_string
-               _atype = v.type_array(_stype)
-               _meth_with_capacity = _atype.local_class.select_method(once "with_capacity".to_symbol)
-               if _meth_with_capacity == null then v.error(self, "{_atype} MUST have a with_capacity method.")
-               _meth_add = _atype.local_class.select_method(once "add".to_symbol)
-               if _meth_add == null then v.error(self, "{_atype} MUST have an add method.")
-               _meth_to_s = v.type_object.local_class.select_method(once "to_s".to_symbol)
-               if _meth_to_s == null then v.error(self, "Object MUST have a to_s method.")
+       redef fun atype do return _atype.as(not null)
+       var _atype: nullable MMType
+       redef fun after_typing(v)
+       do
+               var stype = v.type_string
+               _stype = stype
+               var atype = v.type_array(stype)
+               _atype = atype
                _is_typed = true
        end
 end
 
 redef class ANullExpr
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                _stype = v.type_none
                _is_typed = true
@@ -941,32 +914,21 @@ redef class ANullExpr
 end
 
 redef class AArrayExpr
-       readable attr _meth_with_capacity: MMMethod
-       readable attr _meth_add: MMMethod
-
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                var stype = v.check_conform_multiexpr(null, n_exprs)
-               if stype == null then return
-               do_typing(v, stype)
+               if stype != null then do_typing(v, stype)
        end
 
-       private meth do_typing(v: TypingVisitor, element_type: MMType)
+       private fun do_typing(v: TypingVisitor, element_type: MMType)
        do
                _stype = v.type_array(element_type)
-
-               _meth_with_capacity = _stype.local_class.select_method(once "with_capacity".to_symbol)
-               if _meth_with_capacity == null then v.error(self, "{_stype} MUST have a with_capacity method.")
-               _meth_add = _stype.local_class.select_method(once "add".to_symbol)
-               if _meth_add == null then v.error(self, "{_stype} MUST have an add method.")
-
                _is_typed = true
        end
 end
 
 redef class ARangeExpr
-       readable attr _meth_init: MMMethod
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                if not v.check_expr(n_expr) or not v.check_expr(n_expr2) then return
                var ntype = n_expr.stype
@@ -984,27 +946,10 @@ redef class ARangeExpr
        end
 end
 
-redef class ACrangeExpr
-       redef meth after_typing(v)
-       do
-               super
-               _meth_init = stype.local_class.select_method(once "init".to_symbol)
-       end
-end
-redef class AOrangeExpr
-       redef meth after_typing(v)
-       do
-               super
-               _meth_init = stype.local_class.select_method(once "without_last".to_symbol)
-       end
-end
-
-
 redef class ASuperExpr
-special ASuperInitCall
-       # readable attr _prop: MMSrcMethod
-       readable attr _init_in_superclass: MMMethod
-       redef meth after_typing(v)
+       redef readable var _init_in_superclass: nullable MMMethod
+       redef fun compute_raw_arguments do return n_args.to_a
+       redef fun after_typing(v)
        do
                var precs: Array[MMLocalProperty] = v.local_property.prhe.direct_greaters
                if not precs.is_empty then
@@ -1030,27 +975,27 @@ special ASuperInitCall
                        _init_in_superclass = p
                        register_super_init_call(v, p)
                        if n_args.length > 0 then
-                               var signature = get_signature(v, v.self_var.stype, p, true)
-                               _arguments = process_signature(v, signature, p.name, n_args.to_a)
+                               var signature = get_signature(v, v.self_var.stype.as(not null), p, true)
+                               process_signature(v, signature, p.name, compute_raw_arguments)
                        end
                else
                        v.error(self, "Error: No super method to call for {v.local_property}.")
                        return
                end
 
-               if precs.first.signature_for(v.self_var.stype).return_type != null then
+               if precs.first.signature_for(v.self_var.stype.as(not null)).return_type != null then
                        var stypes = new Array[MMType]
-                       var stype: MMType = null
+                       var stype: nullable MMType = null
                        for prop in precs do
                                assert prop isa MMMethod
-                               var t = prop.signature_for(v.self_var.stype).return_type.for_module(v.module).adapt_to(v.local_property.signature.recv)
+                               var t = prop.signature_for(v.self_var.stype.as(not null)).return_type.for_module(v.module).adapt_to(v.local_property.signature.recv)
                                stypes.add(t)
                                if stype == null or stype < t then
                                        stype = t
                                end
                        end
                        for t in stypes do
-                               v.check_conform(self, t, stype)
+                               v.check_conform(self, t, stype.as(not null))
                        end
                        _stype = stype
                end
@@ -1062,14 +1007,14 @@ special ASuperInitCall
 end
 
 redef class AAttrFormExpr
-       # Attribute accessed
-       readable attr _prop: MMAttribute
+       redef fun prop do return _prop.as(not null)
+       var _prop: nullable MMAttribute
 
-       # Attribute type of the acceded attribute
-       readable attr _attr_type: MMType
+       redef fun attr_type do return _attr_type.as(not null)
+       var _attr_type: nullable MMType
 
        # Compute the attribute accessed
-       private meth do_typing(v: TypingVisitor)
+       private fun do_typing(v: TypingVisitor)
        do
                if not v.check_expr(n_expr) then return
                var type_recv = n_expr.stype
@@ -1091,82 +1036,109 @@ redef class AAttrFormExpr
 end
 
 redef class AAttrExpr
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                do_typing(v)
-               if prop == null then return
+               if _prop == null then return
                _stype = attr_type
                _is_typed = true
        end
 end
 
 redef class AAttrAssignExpr
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                do_typing(v)
-               if prop == null then return
+               if _prop == null then return
                if not v.check_conform_expr(n_value, attr_type) then return
                _is_typed = true
        end
 end
 
 redef class AAttrReassignExpr
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                do_typing(v)
-               if prop == null then return
-               do_lvalue_typing(v, attr_type)
+               if _prop == null then return
+               var t = do_rvalue_typing(v, attr_type)
+               if t == null then return
+               v.check_conform(self, t, n_value.stype)
+               _is_typed = true
+       end
+end
+
+redef class AIssetAttrExpr
+       redef fun after_typing(v)
+       do
+               do_typing(v)
+               if _prop == null then return
+               if attr_type.is_nullable then
+                       v.error(self, "Error: isset on a nullable attribute.")
+               end
+               _stype = v.type_bool
                _is_typed = true
        end
 end
 
-class AAbsAbsSendExpr
-special PExpr
+redef class AAbsAbsSendExpr
        # The signature of the called property
-       readable attr _prop_signature: MMSignature
+       redef fun prop_signature do return _prop_signature.as(not null)
+       var _prop_signature: nullable MMSignature
+
+       # Raw arguments used (without vararg transformation)
+       redef fun raw_arguments: Array[AExpr]
+       do
+               var res = _raw_arguments_cache
+               if res != null then
+                       return res
+               else
+                       res = compute_raw_arguments
+                       if res == null then res = new Array[AExpr]
+                       _raw_arguments_cache = res
+                       return res
+               end
+       end
 
-       # The real arguments used (after star transformation) (once computed)
-       readable attr _arguments: Array[PExpr]
+       var _raw_arguments_cache: nullable Array[AExpr] = null
+
+       fun compute_raw_arguments: nullable Array[AExpr]
+       do
+               print "{location} no compute_raw_arguments"
+               return null
+       end
 
        # Check the conformity of a set of arguments `raw_args' to a signature.
-       private meth process_signature(v: TypingVisitor, psig: MMSignature, name: Symbol, raw_args: Array[PExpr]): Array[PExpr]
+       private fun process_signature(v: TypingVisitor, psig: MMSignature, name: Symbol, raw_args: nullable Array[AExpr]): Bool
        do
                var par_vararg = psig.vararg_rank
                var par_arity = psig.arity
                var raw_arity: Int
                if raw_args == null then raw_arity = 0 else raw_arity = raw_args.length
                if par_arity > raw_arity or (par_arity != raw_arity and par_vararg == -1) then
-                       v.error(self, "Error: '{name}' arity missmatch.")
-                       return null
+                       v.error(self, "Error: arity missmatch; prototype is '{name}{psig}'.")
+                       return false
                end
                var arg_idx = 0
-               var args = new Array[PExpr]
                for par_idx in [0..par_arity[ do
-                       var a: PExpr
+                       var a: AExpr
                        var par_type = psig[par_idx]
                        if par_idx == par_vararg then
-                               var star = new Array[PExpr]
                                for i in [0..(raw_arity-par_arity)] do
                                        a = raw_args[arg_idx]
                                        v.check_conform_expr(a, par_type)
-                                       star.add(a)
                                        arg_idx = arg_idx + 1
                                end
-                               var aa = new AArrayExpr.init_aarrayexpr(star)
-                               aa.do_typing(v, par_type)
-                               a = aa
                        else
                                a = raw_args[arg_idx]
                                v.check_conform_expr(a, par_type)
                                arg_idx = arg_idx + 1
                        end
-                       args.add(a)
                end
-               return args
+               return true
        end
 
        # Check the conformity of a set of defined closures
-       private meth process_closures(v: TypingVisitor, psig: MMSignature, name: Symbol, cd: Array[PClosureDef]): MMType
+       private fun process_closures(v: TypingVisitor, psig: MMSignature, name: Symbol, cd: nullable Array[AClosureDef]): nullable MMType
        do
                var t = psig.return_type
                var cs = psig.closures # Declared closures
@@ -1174,24 +1146,40 @@ special PExpr
                for c in cs do
                        if not c.is_optional then min_arity += 1
                end
-               if cd != null then
-                       if cs.length == 0 then
-                               v.error(self, "Error: {name} does not require blocks.")
-                       else if cd.length > cs.length or cd.length < min_arity then
+               var arity = 0
+               if cd != null then arity = cd.length
+               if cs.length > 0 then
+                       if arity == 0 and min_arity > 0 then
+                               v.error(self, "Error: {name} requires {cs.length} blocks.")
+                       else if arity > cs.length or arity < min_arity then
                                v.error(self, "Error: {name} requires {cs.length} blocks, {cd.length} found.")
                        else
                                # Initialize the break list if a value is required for breaks (ie. if the method is a function)
-                               var break_list: Array[ABreakExpr] = null
+                               var break_list: nullable Array[ABreakExpr] = null
                                if t != null then break_list = new Array[ABreakExpr]
 
+                               # The n_label, is any in only set on the last decl
+                               var n_label = if arity > 0 then cd[arity-1].n_label else null
+
                                # Process each closure definition
-                               for i in [0..cd.length[ do
-                                       var csi = cs[i]
+                               for i in [0..arity[ do
                                        var cdi = cd[i]
-                                       var esc = new EscapableClosure(cdi, csi, break_list)
-                                       v.escapable_ctx.push(esc)
-                                       cdi.accept_typing2(v, esc)
-                                       v.escapable_ctx.pop
+                                       var cni = cdi.n_id.to_symbol
+                                       var csi = psig.closure_named(cni)
+                                       if csi != null then
+                                               var esc = new EscapableClosure(cdi, csi, break_list)
+                                               v.escapable_ctx.push(esc, n_label)
+                                               cdi.accept_typing2(v, esc)
+                                               v.escapable_ctx.pop
+                                       else if cs.length == 1 then
+                                               v.error(cdi.n_id, "Error: no closure named '!{cni}' in {name}; only closure is !{cs.first.name}.")
+                                       else
+                                               var a = new Array[String]
+                                               for c in cs do
+                                                       a.add("!{c.name}")
+                                               end
+                                               v.error(cdi.n_id, "Error: no closure named '!{cni}' in {name}; only closures are {a.join(",")}.")
+                                       end
                                end
 
                                # Check break type conformity
@@ -1199,37 +1187,32 @@ special PExpr
                                        t = v.check_conform_multiexpr(t, break_list)
                                end
                        end
-               else if min_arity != 0 then
-                       v.error(self, "Error: {name} requires {cs.length} blocks.")
+               else if arity != 0 then
+                       v.error(self, "Error: {name} does not require blocks.")
                end
                return t
        end
 end
 
-class AAbsSendExpr
-special AAbsAbsSendExpr
+redef class AAbsSendExpr
        # Compute the called global property
-       private meth do_typing(v: TypingVisitor, type_recv: MMType, is_implicit_self: Bool, recv_is_self: Bool, name: Symbol, raw_args: Array[PExpr], closure_defs: Array[PClosureDef])
+       private fun do_typing(v: TypingVisitor, type_recv: MMType, is_implicit_self: Bool, recv_is_self: Bool, name: Symbol, raw_args: nullable Array[AExpr], closure_defs: nullable Array[AClosureDef])
        do
                var prop = get_property(v, type_recv, is_implicit_self, name)
                if prop == null then return
                var sig = get_signature(v, type_recv, prop, recv_is_self)
-               if sig == null then return
-               var args = process_signature(v, sig, prop.name, raw_args)
-               if args == null then return
+               if not process_signature(v, sig, prop.name, raw_args) then return
                var rtype = process_closures(v, sig, prop.name, closure_defs)
                if rtype == null and sig.return_type != null then return
                _prop = prop
                _prop_signature = sig
-               _arguments = args
                _return_type = rtype
        end
 
-       private meth get_property(v: TypingVisitor, type_recv: MMType, is_implicit_self: Bool, name: Symbol): MMMethod
+       private fun get_property(v: TypingVisitor, type_recv: MMType, is_implicit_self: Bool, name: Symbol): nullable MMMethod
        do
-               if type_recv == null then return null
                var lc = type_recv.local_class
-               var prop: MMMethod = null
+               var prop: nullable MMMethod = null
                if lc.has_global_property_by_name(name) then prop = lc.select_method(name)
                if prop == null and v.local_property.global.is_init then
                        var props = type_recv.local_class.super_methods_named(name)
@@ -1255,7 +1238,7 @@ special AAbsAbsSendExpr
        end
 
        # Get the signature for a local property and a receiver
-       private meth get_signature(v: TypingVisitor, type_recv: MMType, prop: MMMethod, recv_is_self: Bool): MMSignature
+       private fun get_signature(v: TypingVisitor, type_recv: MMType, prop: MMMethod, recv_is_self: Bool): MMSignature
        do
                prop.global.check_visibility(v, self, v.module, recv_is_self)
                var psig = prop.signature_for(type_recv)
@@ -1264,25 +1247,26 @@ special AAbsAbsSendExpr
        end
 
        # The invoked method (once computed)
-       readable attr _prop: MMMethod
+       redef fun prop do return _prop.as(not null)
+       var _prop: nullable MMMethod
 
        # The return type (if any) (once computed)
-       readable attr _return_type: MMType
+       redef readable var _return_type: nullable MMType
 end
 
 # A possible call of constructor in a super class
 # Could be an explicit call or with the 'super' keyword
-class ASuperInitCall
-special AAbsSendExpr
-       private meth register_super_init_call(v: TypingVisitor, property: MMMethod)
+redef class ASuperInitCall
+       private fun register_super_init_call(v: TypingVisitor, property: MMMethod)
        do
                if parent != v.top_block and self != v.top_block then
                        v.error(self, "Error: Constructor invocation {property} must not be in nested block.")
                end
                var cla = v.module[property.global.intro.local_class.global]
-               var prev_class: MMLocalClass = null
-               if not v.explicit_super_init_calls.is_empty then
-                       prev_class = v.explicit_super_init_calls.last.global.intro.local_class
+               var prev_class: nullable MMLocalClass = null
+               var esic = v.explicit_super_init_calls.as(not null)
+               if not esic.is_empty then
+                       prev_class = esic.last.global.intro.local_class
                end
                var order = v.local_class.cshe.reverse_linear_extension
                if cla == v.local_class then
@@ -1300,7 +1284,7 @@ special AAbsSendExpr
                                        if not last_is_found then
                                                v.error(self, "Error: Constructor of {c} must be invoked before constructor of {prev_class}")
                                        end
-                                       v.explicit_super_init_calls.add(property)
+                                       esic.add(property)
                                        break
                                end
                        end
@@ -1310,11 +1294,11 @@ special AAbsSendExpr
 end
 
 redef class ANewExpr
-special AAbsSendExpr
-       redef meth after_typing(v)
+       redef fun compute_raw_arguments do return n_args.to_a
+       redef fun after_typing(v)
        do
+               if not n_type.is_typed then return
                var t = n_type.stype
-               if t == null then return
                if t.local_class.global.is_abstract then
                        v.error(self, "Error: try to instantiate abstract class {t.local_class}.")
                        return
@@ -1326,8 +1310,8 @@ special AAbsSendExpr
                        name = n_id.to_symbol
                end
 
-               do_typing(v, t, false, false, name, n_args.to_a, null)
-               if prop == null then return
+               do_typing(v, t, false, false, name, raw_arguments, null)
+               if _prop == null then return
 
                if not prop.global.is_init then
                        v.error(self, "Error: {prop} is not a constructor.")
@@ -1340,26 +1324,23 @@ end
 
 
 redef class ASendExpr
-special ASuperInitCall
        # Name of the invoked property
-       meth name: Symbol is abstract 
-
-       # Raw arguments used (withour star transformation)
-       meth raw_arguments: Array[PExpr] is abstract
+       fun name: Symbol is abstract 
 
        # Closure definitions
-       meth closure_defs: Array[PClosureDef] do return null
+       redef fun closure_defs: nullable Array[AClosureDef] do return null
 
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                do_all_typing(v)
        end
 
-       private meth do_all_typing(v: TypingVisitor)
+       private fun do_all_typing(v: TypingVisitor)
        do
                if not v.check_expr(n_expr) then return
                do_typing(v, n_expr.stype, n_expr.is_implicit_self, n_expr.is_self, name, raw_arguments, closure_defs)
-               if prop == null then return
+               if _prop == null then return
+               var prop = _prop.as(not null)
 
                if prop.global.is_init then
                        if not v.local_property.global.is_init then
@@ -1376,15 +1357,15 @@ special ASuperInitCall
        end
 end
 
-class ASendReassignExpr
-special ASendExpr
-special AReassignFormExpr
-       readable attr _read_prop: MMMethod
-       redef meth do_all_typing(v)
+redef class ASendReassignExpr
+       redef fun read_prop do return _read_prop.as(not null)
+       var _read_prop: nullable MMMethod
+       redef fun do_all_typing(v)
        do
                if not v.check_expr(n_expr) then return
                var raw_args = raw_arguments
                do_typing(v, n_expr.stype, n_expr.is_implicit_self, n_expr.is_self, name, raw_args, null)
+               var prop = _prop
                if prop == null then return
                if prop.global.is_init then
                        if not v.local_property.global.is_init then
@@ -1393,17 +1374,18 @@ special AReassignFormExpr
                                v.error(self, "Error: constructor {prop} is not invoken on 'self'.")
                        end
                end
-               var t = prop.signature_for(n_expr.stype).return_type
+               var t = prop.signature_for(n_expr.stype).return_type.as(not null)
                if not n_expr.is_self then t = t.not_for_self
 
-               do_lvalue_typing(v, t)
+               var t2 = do_rvalue_typing(v, t)
+               if t2 == null then return
+               v.check_conform(self, t2, n_value.stype)
 
                _read_prop = prop
-               var old_args = arguments
+               raw_args = raw_args.to_a
                raw_args.add(n_value)
 
                do_typing(v, n_expr.stype, n_expr.is_implicit_self, n_expr.is_self, "{name}=".to_symbol, raw_args, null)
-               if prop == null then return
                if prop.global.is_init then
                        if not v.local_property.global.is_init then
                                v.error(self, "Error: try to invoke constructor {prop} in a method.")
@@ -1412,89 +1394,132 @@ special AReassignFormExpr
                        end
                end
 
-               _arguments = old_args # FIXME: What if star parameters do not match betwen the two methods?
                _is_typed = true
        end
 end
 
 redef class ABinopExpr
-       redef meth raw_arguments do return [n_expr2]
+       redef fun compute_raw_arguments do return [n_expr2]
 end
 redef class AEqExpr
-       redef meth name do return once "==".to_symbol
+       redef fun name do return once "==".to_symbol
+       redef fun after_typing(v)
+       do
+               super
+               if not n_expr.is_typed or not n_expr2.is_typed then return
+               if n_expr.stype isa MMTypeNone and not n_expr2.stype.is_nullable or
+               n_expr2.stype isa MMTypeNone and not n_expr.stype.is_nullable then
+                       v.warning(self, "Warning: comparaison between null and a non nullable value.")
+               end
+
+               if n_expr.stype isa MMTypeNone then
+                       try_to_isa(v, n_expr2)
+               else if n_expr2.stype isa MMTypeNone then
+                       try_to_isa(v, n_expr)
+               end
+       end
+
+       private fun try_to_isa(v: TypingVisitor, n: AExpr)
+       do
+               var variable = n.its_variable
+               if variable != null then
+                       _if_false_variable_ctx = v.variable_ctx.sub_with(self, variable, n.stype.as_notnull)
+               end
+       end
 end
 redef class ANeExpr
-       redef meth name do return once "!=".to_symbol
+       redef fun name do return once "!=".to_symbol
+       redef fun after_typing(v)
+       do
+               super
+               if not n_expr.is_typed or not n_expr2.is_typed then return
+               if n_expr.stype isa MMTypeNone and not n_expr2.stype.is_nullable or
+               n_expr2.stype isa MMTypeNone and not n_expr.stype.is_nullable then
+                       v.warning(self, "Warning: comparaison between null and a non nullable value.")
+               end
+
+               if n_expr.stype isa MMTypeNone then
+                       try_to_isa(v, n_expr2)
+               else if n_expr2.stype isa MMTypeNone then
+                       try_to_isa(v, n_expr)
+               end
+       end
+
+       private fun try_to_isa(v: TypingVisitor, n: AExpr)
+       do
+               var variable = n.its_variable
+               if variable != null then
+                       _if_true_variable_ctx = v.variable_ctx.sub_with(self, variable, n.stype.as_notnull)
+               end
+       end
 end
 redef class ALtExpr
-       redef meth name do return once "<".to_symbol
+       redef fun name do return once "<".to_symbol
 end
 redef class ALeExpr
-       redef meth name do return once "<=".to_symbol
+       redef fun name do return once "<=".to_symbol
 end
 redef class AGtExpr
-       redef meth name do return once ">".to_symbol
+       redef fun name do return once ">".to_symbol
 end
 redef class AGeExpr
-       redef meth name do return once ">=".to_symbol
+       redef fun name do return once ">=".to_symbol
 end
 redef class APlusExpr
-       redef meth name do return once "+".to_symbol
+       redef fun name do return once "+".to_symbol
 end
 redef class AMinusExpr
-       redef meth name do return once "-".to_symbol
+       redef fun name do return once "-".to_symbol
 end
 redef class AStarshipExpr
-       redef meth name do return once "<=>".to_symbol
+       redef fun name do return once "<=>".to_symbol
 end
 redef class AStarExpr
-       redef meth name do return once "*".to_symbol
+       redef fun name do return once "*".to_symbol
 end
 redef class ASlashExpr
-       redef meth name do return once "/".to_symbol
+       redef fun name do return once "/".to_symbol
 end
 redef class APercentExpr
-       redef meth name do return once "%".to_symbol
+       redef fun name do return once "%".to_symbol
 end
 
 redef class AUminusExpr
-       redef meth name do return once "unary -".to_symbol
-       redef meth raw_arguments do return null
+       redef fun name do return once "unary -".to_symbol
+       redef fun compute_raw_arguments do return null
 end
 
 redef class ACallFormExpr
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
-               if n_expr != null and n_expr.is_implicit_self then
+               if n_expr.is_implicit_self then
                        var name = n_id.to_symbol
                        var variable = v.variable_ctx[name]
                        if variable != null then
+                               var n: AExpr
                                if variable isa ClosureVariable then
-                                       var n = new AClosureCallExpr.init_aclosurecallexpr(n_id, n_args, n_closure_defs)
-                                       replace_with(n)
-                                       n.variable = variable
-                                       n.after_typing(v)
-                                       return
+                                       n = new AClosureCallExpr.init_aclosurecallexpr(n_id, n_args, n_closure_defs)
+                                       n._variable = variable
                                else
                                        if not n_args.is_empty then
                                                v.error(self, "Error: {name} is variable, not a function.")
                                                return
                                        end
-                                       var vform = variable_create(variable)
-                                       vform.variable = variable
-                                       replace_with(vform)
-                                       vform.after_typing(v)
-                                       return
+                                       n = variable_create(variable)
+                                       n._variable = variable
                                end
+                               replace_with(n)
+                               n.after_typing(v)
+                               return
                        end
                end
 
                super
        end
 
-       redef meth closure_defs
+       redef fun closure_defs
        do
-               if n_closure_defs == null or n_closure_defs.is_empty then
+               if n_closure_defs.is_empty then
                        return null
                else
                        return n_closure_defs.to_a
@@ -1502,27 +1527,27 @@ redef class ACallFormExpr
        end
 
        # Create a variable acces corresponding to the call form
-       meth variable_create(variable: Variable): AVarFormExpr is abstract
+       fun variable_create(variable: Variable): AVarFormExpr is abstract
 end
 
 redef class ACallExpr
-       redef meth variable_create(variable)
+       redef fun variable_create(variable)
        do
                return new AVarExpr.init_avarexpr(n_id)
        end
 
-       redef meth name do return n_id.to_symbol
-       redef meth raw_arguments do return n_args.to_a
+       redef fun name do return n_id.to_symbol
+       redef fun compute_raw_arguments do return n_args.to_a
 end
 
 redef class ACallAssignExpr
-       redef meth variable_create(variable)
+       redef fun variable_create(variable)
        do
                return new AVarAssignExpr.init_avarassignexpr(n_id, n_assign, n_value)
        end
 
-       redef meth name do return (n_id.text + "=").to_symbol
-       redef meth raw_arguments do
+       redef fun name do return (n_id.text + "=").to_symbol
+       redef fun compute_raw_arguments do
                var res = n_args.to_a
                res.add(n_value)
                return res
@@ -1530,24 +1555,31 @@ redef class ACallAssignExpr
 end
 
 redef class ACallReassignExpr
-special ASendReassignExpr
-       redef meth variable_create(variable)
+       redef fun variable_create(variable)
        do
                return new AVarReassignExpr.init_avarreassignexpr(n_id, n_assign_op, n_value)
        end
 
-       redef meth name do return n_id.to_symbol
-       redef meth raw_arguments do return n_args.to_a
+       redef fun name do return n_id.to_symbol
+       redef fun compute_raw_arguments do return n_args.to_a
 end
 
 redef class ABraExpr
-       redef meth name do return once "[]".to_symbol
-       redef meth raw_arguments do return n_args.to_a
+       redef fun name do return once "[]".to_symbol
+       redef fun compute_raw_arguments do return n_args.to_a
+       redef fun closure_defs
+       do
+               if n_closure_defs.is_empty then
+                       return null
+               else
+                       return n_closure_defs.to_a
+               end
+       end
 end
 
 redef class ABraAssignExpr
-       redef meth name do return once "[]=".to_symbol
-       redef meth raw_arguments do
+       redef fun name do return once "[]=".to_symbol
+       redef fun compute_raw_arguments do
                var res = n_args.to_a
                res.add(n_value)
                return res
@@ -1555,67 +1587,79 @@ redef class ABraAssignExpr
 end
 
 redef class ABraReassignExpr
-special ASendReassignExpr
-       redef meth name do return once "[]".to_symbol
-       redef meth raw_arguments do return n_args.to_a
+       redef fun name do return once "[]".to_symbol
+       redef fun compute_raw_arguments do return n_args.to_a
 end
 
 redef class AInitExpr
-       redef meth name do return once "init".to_symbol
-       redef meth raw_arguments do return n_args.to_a
+       redef fun name do return once "init".to_symbol
+       redef fun compute_raw_arguments do return n_args.to_a
 end
 
 redef class AClosureCallExpr
-special AAbsAbsSendExpr
-       redef meth after_typing(v)
+       var _variable: nullable ClosureVariable
+       redef fun variable do return _variable.as(not null)
+       redef fun compute_raw_arguments do return n_args.to_a
+
+       redef fun after_typing(v)
        do
                var va = variable
                if va.closure.is_break then v.variable_ctx.unreash = true
                var sig = va.closure.signature
-               var args = process_signature(v, sig, n_id.to_symbol, n_args.to_a)
+               var s = process_signature(v, sig, n_id.to_symbol, compute_raw_arguments)
                if not n_closure_defs.is_empty then
                        process_closures(v, sig, n_id.to_symbol, n_closure_defs.to_a)
                end
-               if args == null then return
+               if not s then return
                _prop_signature = sig
-               _arguments = args
                _stype = sig.return_type
                _is_typed = true
        end
 end
 
-redef class PClosureDef
+redef class AClosureId
+       fun to_symbol: Symbol is abstract
+end
+redef class ASimpleClosureId
+       redef fun to_symbol: Symbol do return n_id.to_symbol
+end
+redef class ABreakClosureId
+       redef fun to_symbol: Symbol do return n_kwbreak.to_symbol
+end
+
+redef class AClosureDef
+       var _closure: nullable MMClosure
+       redef fun closure do return _closure.as(not null)
+
        # The corresponding escapable object
-       readable attr _escapable: EscapableBlock
+       readable var _escapable: nullable EscapableBlock
 
-       attr _accept_typing2: Bool
-       redef meth accept_typing(v)
+       var _accept_typing2: Bool = false
+       redef fun accept_typing(v)
        do
                # Typing is deferred, wait accept_typing2(v)
                if _accept_typing2 then super
        end
 
-       private meth accept_typing2(v: TypingVisitor, esc: EscapableClosure) is abstract
-end
-
-redef class AClosureDef
-       redef meth accept_typing2(v, esc)
+       private fun accept_typing2(v: TypingVisitor, esc: EscapableClosure)
        do
                _escapable = esc
 
                var sig = esc.closure.signature
-               if sig.arity != n_id.length then
-                       v.error(self, "Error: {sig.arity} automatic variable names expected, {n_id.length} found.")
+               if sig.arity != n_ids.length then
+                       v.error(self, "Error: {sig.arity} automatic variable names expected, {n_ids.length} found.")
                        return
                end
 
-               closure = esc.closure
+               _closure = esc.closure
 
                var old_var_ctx = v.variable_ctx
+               var old_base_var_ctx = v.base_variable_ctx
+               v.base_variable_ctx = v.variable_ctx
                v.variable_ctx = v.variable_ctx.sub(self)
                variables = new Array[AutoVariable]
-               for i in [0..n_id.length[ do
-                       var va = new AutoVariable(n_id[i].to_symbol, self)
+               for i in [0..n_ids.length[ do
+                       var va = new AutoVariable(n_ids[i].to_symbol, n_ids[i])
                        variables.add(va)
                        va.stype = sig[i]
                        v.variable_ctx.add(va)
@@ -1632,29 +1676,44 @@ redef class AClosureDef
                        end
                end
                v.variable_ctx = old_var_ctx
+               v.base_variable_ctx = old_base_var_ctx
        end
 end
 
 class ATypeCheckExpr
-special PExpr
-       private meth check_expr_cast(v: TypingVisitor, n_expr: PExpr, n_type: PType)
+special AExpr
+       private fun check_expr_cast(v: TypingVisitor, n_expr: AExpr, n_type: AType)
        do
                if not v.check_expr(n_expr) then return
+               if not n_type.is_typed then return
                var etype = n_expr.stype
                var ttype = n_type.stype
                if etype == ttype then
                        v.warning(self, "Warning: Expression is already a {ttype}.")
                else if etype < ttype then
                        v.warning(self, "Warning: Expression is already a {ttype} since it is a {etype}.")
+               else if etype.is_nullable and etype.as_notnull == ttype then
+                       if ttype isa MMTypeFormal and ttype.bound.is_nullable then
+                               # No warning in this case since with
+                               #   type T: nullable A
+                               #   var x: nullable T
+                               # 'x.as(not null)' != 'x.as(T)'
+                               # 'x != null' != 'x isa T'
+                       else if self isa AIsaExpr then
+                               v.warning(self, "Warning: Prefer '!= null'.")
+                       else
+                               v.warning(self, "Warning: Prefer '.as(not null)'.")
+                       end
                end
        end
 end
 
 redef class AIsaExpr
 special ATypeCheckExpr
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                check_expr_cast(v, n_expr, n_type)
+               if not n_type.is_typed then return
                var variable = n_expr.its_variable
                if variable != null then
                        _if_true_variable_ctx = v.variable_ctx.sub_with(self, variable, n_type.stype)
@@ -1666,16 +1725,33 @@ end
 
 redef class AAsCastExpr
 special ATypeCheckExpr
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                check_expr_cast(v, n_expr, n_type)
+               if not n_type.is_typed then return
                _stype = n_type.stype
                _is_typed = _stype != null
        end
 end
 
+redef class AAsNotnullExpr
+       redef fun after_typing(v)
+       do
+               if not v.check_expr(n_expr) then return
+               var t = n_expr.stype
+               if t isa MMTypeNone then
+                       v.error(n_expr, "Type error: 'as(not null)' on 'null' value.")
+                       return
+               else if not t.is_nullable then
+                       v.warning(n_expr, "Warning: 'as(not null)' on non nullable type.")
+               end
+               _stype = n_expr.stype.as_notnull
+               _is_typed = true
+       end
+end
+
 redef class AProxyExpr
-       redef meth after_typing(v)
+       redef fun after_typing(v)
        do
                if not n_expr.is_typed then return
                _is_typed = true
@@ -1685,7 +1761,7 @@ redef class AProxyExpr
 end
 
 redef class AOnceExpr
-       redef meth accept_typing(v)
+       redef fun accept_typing(v)
        do
                if v.once_count > 0 then
                        v.warning(self, "Useless once in a once expression.")