syntax: comparing a variable with null makes it evolve to null

[nit.git] / src / syntax / typing.nit

# This file is part of NIT ( http://www.nitlanguage.org ).
#
# Copyright 2008 Jean Privat <jean@pryen.org>
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# Analysis property bodies, statements and expressions
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
        fun do_typing(tc: ToolContext)
        do
                var tv = new TypingVisitor(tc, self)
                tv.enter_visit(node)
        end
end

# Typing visitor
# * Associate local variables to nodes
# * Distinguish method call and local variable access
# * Resolve call and attribute access
# * Check type conformance
private class TypingVisitor
special AbsSyntaxVisitor
        redef fun visit(n)
        do
                if n != null then n.accept_typing(self)
        end

        # Current knowledge about variables names and types
        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 var _escapable_ctx: EscapableContext = new EscapableContext(self)

        # The current reciever
        fun self_var: ParamVariable do return _self_var.as(not null)
        writable var _self_var: nullable ParamVariable

        # Block of the current method
        readable writable var _top_block: nullable AExpr

        # List of explicit invocation of constructors of super-classes
        readable writable var _explicit_super_init_calls: nullable Array[MMMethod]

        # Is a other constructor of the same class invoked
        readable writable var _explicit_other_init_call: Bool = false

        # Make the if_true_variable_ctx of the expression effective
        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

        # 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 var _once_count: Int = 0

        init(tc, module) do super

        private fun get_default_constructor_for(n: ANode, c: MMLocalClass, prop: MMSrcMethod): nullable MMMethod
        do
                var v = self
                #var prop = v.local_property
                #assert prop isa MMMethod
                var candidates = new Array[MMMethod]
                var false_candidates = new Array[MMMethod]
                var parity = prop.signature.arity
                for g in c.global_properties do
                        if not g.is_init_for(c) then continue
                        var gp = c[g]
                        var gps = gp.signature_for(c.get_type)
                        assert gp isa MMSrcMethod
                        var garity = gps.arity
                        if gp.name == prop.name then
                                if garity == 0 or (parity == garity and prop.signature < gps) then
                                        return gp
                                else
                                        false_candidates.add(gp)
                                end
                        else if garity == 0 and gp.name == once ("init".to_symbol) then
                                candidates.add(gp)
                                false_candidates.add(gp)
                        else
                                false_candidates.add(gp)
                        end
                end
                if candidates.length == 1 then
                        return candidates.first
                else if candidates.length > 0 then
                        var a = new Array[String]
                        for p in candidates do
                                a.add("{p.full_name}{p.signature}")
                        end
                        v.error(n, "Error: Conflicting default constructor to call for {c}: {a.join(", ")}.")
                        return null
                else if false_candidates.length > 0 then
                        var a = new Array[String]
                        for p in false_candidates do
                                a.add("{p.full_name}{p.signature}")
                        end
                        v.error(n, "Error: there is no available compatible constrctor in {c}. Discarded candidates are {a.join(", ")}.")
                        return null
                else
                        v.error(n, "Error: there is no available compatible constrctor in {c}.")
                        return null
                end
        end
end


###############################################################################

redef class ANode
        private fun accept_typing(v: TypingVisitor) 
        do
                accept_abs_syntax_visitor(v)
                after_typing(v)
        end
        private fun after_typing(v: TypingVisitor) do end
end

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 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.as(not null), prop.signature.return_type.as(not null))
                end
                v.variable_ctx = old_var_ctx
        end
end

redef class AMethPropdef
        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
                v.variable_ctx = old_var_ctx
        end
end

redef class AConcreteMethPropdef
        redef fun after_typing(v)
        do
                super
                if v.variable_ctx.unreash == false and method.signature.return_type != null then
                        v.error(self, "Control error: Reached end of function (a 'return' with a value was expected).")
                end
        end
end

redef class AConcreteInitPropdef
        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: 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)
                        end
                        var j = 0
                        while j < v.local_class.cshe.direct_greaters.length do
                                var c = v.local_class.cshe.direct_greaters[j]
                                if c.global.is_interface or c.global.is_universal or c.global.is_mixin then
                                        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.as(not null))
                                        i += 1
                                        if i < l then
                                                cur_m = explicit_super_init_calls[i]
                                                cur_c = cur_m.global.intro.local_class.for_module(v.module)
                                        else
                                                cur_m = null
                                                cur_c = null
                                        end
                                else
                                        var p = v.get_default_constructor_for(self, c, method)
                                        if p != null then
                                                super_init_calls.add(p)
                                        end
                                        j += 1
                                end
                        end
                end
        end
end

redef class AParam
        redef fun after_typing(v)
        do
                v.variable_ctx.add(variable)
        end
end

redef class AClosureDecl
        # The corresponding escapable object
        readable var _escapable: nullable EscapableBlock

        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)

                var blist: nullable Array[AExpr] = null
                var t = v.local_property.signature.return_type
                if t != null then blist = new Array[AExpr]
                var escapable = new EscapableClosure(self, variable.closure, blist)
                _escapable = escapable
                v.escapable_ctx.push(escapable, null)

                super

                if n_expr != null then
                        if v.variable_ctx.unreash == false then
                                if variable.closure.signature.return_type != null then
                                        v.error(self, "Control error: Reached end of block (a 'continue' with a value was expected).")
                                else if variable.closure.is_break and escapable.break_list != null then
                                        v.error(self, "Control error: Reached end of break block (a 'break' with a value was expected).")
                                end
                        end
                end
                if blist != null then for x in blist do
                        v.check_conform_expr(x, t)
                end

                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 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 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 "{location}: not is_typed"
                        abort
                end
                if is_statement then
                        print "{location}: is_statement"
                        abort
                end
                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

        # Is the expression the implicit receiver
        fun is_implicit_self: Bool do return false

        # Is the expression the current receiver (implicit or explicit)
        fun is_self: Bool do return false

        # The variable accessed is any
        fun its_variable: nullable Variable do return null

        # The variable type information if current boolean expression is true
        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
        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, n_id)
                _variable = va
                v.variable_ctx.add(va)
                var ne = n_expr
                if ne != 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 ne != null then
                                v.check_conform_expr(ne, va.stype)
                        end
                else if ne != null then
                        if not v.check_expr(ne) then return
                        va.stype = ne.stype
                else
                        va.stype = v.type_object.as_nullable
                end
                _is_typed = true
        end
end

redef class ABlockExpr
        redef fun accept_typing(v)
        do
                var old_var_ctx = v.variable_ctx
                v.variable_ctx = v.variable_ctx.sub(self)

                for e in n_expr do
                        if v.variable_ctx.unreash and not v.variable_ctx.already_unreash then
                                v.variable_ctx.already_unreash = true
                                v.warning(e, "Warning: unreachable statement.")
                        end
                        v.enter_visit(e)
                end

                old_var_ctx.merge(v.variable_ctx)
                v.variable_ctx = old_var_ctx
                _is_typed = true
        end
end

redef class AReturnExpr
        redef fun after_typing(v)
        do
                v.variable_ctx.unreash = true
                var t = v.local_property.signature.return_type
                var e = n_expr
                if e == null and t != null then
                        v.error(self, "Error: Return without value in a function.")
                else if e != null and t == null then
                        v.error(self, "Error: Return with value in a procedure.")
                else if e != null and t != null then
                        v.check_conform_expr(e, t)
                end
                _is_typed = true
        end
end

redef class AContinueExpr
        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: cannot 'continue', only 'break'.")
                        return
                end

                var t = esc.continue_stype
                if n_expr == null and t != null then
                        v.error(self, "Error: continue with a value required in this block.")
                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.as(not null), t)
                end
                _is_typed = true
        end
end

redef class ABreakExpr
        redef fun after_typing(v)
        do
                v.variable_ctx.unreash = true
                var esc = compute_escapable_block(v.escapable_ctx)
                if esc == null then return

                var bl = esc.break_list
                if n_expr == null and bl != null then
                        v.error(self, "Error: break with a value required in this block.")
                else if n_expr != null and bl == null then
                        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.as(not null))
                end
                _is_typed = true
        end
end

redef class AAbortExpr
        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 fun accept_typing(v)
        do
                var old_var_ctx = v.variable_ctx
                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)

                # 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

                # 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 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 condition
                v.enter_visit(n_expr)
                v.check_conform_expr(n_expr, v.type_bool)

                if n_expr isa ATrueExpr then
                        v.warning(self, "Warning: use 'loop' instead of 'while true do'.")
                end

                # 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 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)
                var va = new AutoVariable(n_id.to_symbol, n_id)
                _variable = va
                v.variable_ctx.add(va)

                # 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

                # 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 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 fun its_variable do return variable

        redef fun after_typing(v)
        do
                v.variable_ctx.check_is_set(self, variable)
                _stype = v.variable_ctx.stype(variable)
                _is_typed = _stype != null
        end
end

redef class AVarAssignExpr
        redef fun after_typing(v)
        do
                v.variable_ctx.mark_is_set(variable)

                # Check the base type
                var btype = v.base_variable_ctx.stype(variable)
                if not v.check_expr(n_value) then return
                if btype != null and 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
        # 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 null
                end
                var name = n_assign_op.method_name
                if type_lvalue isa MMTypeNone then
                        v.error(self, "Error: Method '{name}' call on 'null'.")
                        return null
                end
                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 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 null
                return psig.return_type.not_for_self
        end

        redef fun assign_method do return _assign_method.as(not null)
        var _assign_method: nullable MMMethod
end

redef class AVarReassignExpr
        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)
                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_expr(n_value) then return
                if btype != null and 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 AAssignOp
        fun method_name: Symbol is abstract
end
redef class APlusAssignOp
        redef fun method_name do return once "+".to_symbol
end
redef class AMinusAssignOp
        redef fun method_name do return once "-".to_symbol
end

redef class ASelfExpr
        var _variable: nullable ParamVariable
        redef fun variable do return _variable.as(not null)

        redef fun its_variable do return variable

        redef fun after_typing(v)
        do
                _variable = v.self_var
                _stype = v.variable_ctx.stype(variable)
                _is_typed = true
        end

        redef fun is_self do return true
end

redef class AImplicitSelfExpr
        redef fun is_implicit_self do return true
end

redef class AIfexprExpr
        redef fun accept_typing(v)
        do
                var old_var_ctx = v.variable_ctx

                # 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)

                # Process 'then'
                v.variable_ctx = v.variable_ctx.sub(n_then)
                v.enter_visit(n_then)

                # 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 'else'
                v.variable_ctx = v.variable_ctx.sub(n_else)
                v.enter_visit(n_else)

                # 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

                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 fun after_typing(v)
        do
                _stype = v.type_bool
                _is_typed = true
        end
end

redef class AOrExpr
        redef fun accept_typing(v)
        do
                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 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)

                # Prepare right operand context
                v.use_if_true_variable_ctx(n_expr)

                # 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
                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 ANotExpr
        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 fun after_typing(v)
        do
                _stype = v.type_int
                _is_typed = true
        end
end

redef class AFloatExpr
        redef fun after_typing(v)
        do
                _stype = v.type_float
                _is_typed = true
        end
end

redef class ACharExpr
        redef fun after_typing(v)
        do
                _stype = v.type_char
                _is_typed = true
        end
end

redef class AStringFormExpr
        redef fun after_typing(v)
        do
                _stype = v.type_string
                _is_typed = true
        end
end

redef class ASuperstringExpr
        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 fun after_typing(v)
        do
                _stype = v.type_none
                _is_typed = true
        end
end

redef class AArrayExpr
        redef fun after_typing(v)
        do
                var stype = v.check_conform_multiexpr(null, n_exprs)
                if stype != null then do_typing(v, stype)
        end

        private fun do_typing(v: TypingVisitor, element_type: MMType)
        do
                _stype = v.type_array(element_type)
                _is_typed = true
        end
end

redef class ARangeExpr
        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
                var ntype2 = n_expr2.stype
                if ntype < ntype2 then
                        ntype = ntype2
                else if not ntype2 < ntype then
                        v.error(self, "Type error: {ntype} incompatible with {ntype2}.")
                        return
                end
                var dtype = v.type_discrete
                if not v.check_conform_expr(n_expr, dtype) or not v.check_conform_expr(n_expr2, dtype) then return
                _stype = v.type_range(ntype)
                _is_typed = true
        end
end

redef class ASuperExpr
        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
                        v.local_property.need_super = true
                else if v.local_property.global.is_init then
                        var base_precs = v.local_class.super_methods_named(v.local_property.name)
                        for p in base_precs do
                                if not p.global.is_init then
                                        v.error(self, "Error: {p.local_class}::{p} is not a constructor.")
                                else
                                        precs.add(v.local_class[p.global])
                                end
                        end
                        if precs.is_empty then
                                v.error(self, "Error: No contructor named {v.local_property.name} in superclasses.")
                                return
                        else if precs.length > 1 then
                                v.error(self, "Error: Conflicting contructors named {v.local_property.name} in superclasses: {precs.join(", ")}.")
                                return
                        end
                        var p = base_precs.first
                        assert p isa MMMethod
                        _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.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.as(not null)).return_type != null then
                        var stypes = new Array[MMType]
                        var stype: nullable MMType = null
                        for prop in precs do
                                assert prop isa MMMethod
                                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.as(not null))
                        end
                        _stype = stype
                end
                var p = v.local_property
                assert p isa MMSrcMethod
                _prop = p
                _is_typed = true
        end
end

redef class AAttrFormExpr
        redef fun prop do return _prop.as(not null)
        var _prop: nullable MMAttribute

        redef fun attr_type do return _attr_type.as(not null)
        var _attr_type: nullable MMType

        # Compute the attribute accessed
        private fun do_typing(v: TypingVisitor)
        do
                if not v.check_expr(n_expr) then return
                var type_recv = n_expr.stype
                var name = n_id.to_symbol
                if type_recv isa MMTypeNone then
                        v.error(self, "Error: Attribute '{name}' access on 'null'.")
                        return
                end
                var lc = type_recv.local_class
                if not lc.has_global_property_by_name(name) then
                        v.error(self, "Error: Attribute {name} doesn't exists in {type_recv}.")
                        return
                end
                var prop = lc.select_attribute(name)
                if v.module.visibility_for(prop.global.local_class.module) < 3 then
                        v.error(self, "Error: Attribute {name} from {prop.global.local_class.module} is invisible in {v.module}")
                end
                _prop = prop
                var at = prop.signature_for(type_recv).return_type 
                if not n_expr.is_self then at = at.not_for_self
                _attr_type = at
        end
end

redef class AAttrExpr
        redef fun after_typing(v)
        do
                do_typing(v)
                if _prop == null then return
                _stype = attr_type
                _is_typed = true
        end
end

redef class AAttrAssignExpr
        redef fun after_typing(v)
        do
                do_typing(v)
                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 fun after_typing(v)
        do
                do_typing(v)
                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

redef class AAbsAbsSendExpr
        # The signature of the called property
        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

        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 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: arity missmatch; prototype is '{name}{psig}'.")
                        return false
                end
                var arg_idx = 0
                for par_idx in [0..par_arity[ do
                        var a: AExpr
                        var par_type = psig[par_idx]
                        if par_idx == par_vararg then
                                for i in [0..(raw_arity-par_arity)] do
                                        a = raw_args[arg_idx]
                                        v.check_conform_expr(a, par_type)
                                        arg_idx = arg_idx + 1
                                end
                        else
                                a = raw_args[arg_idx]
                                v.check_conform_expr(a, par_type)
                                arg_idx = arg_idx + 1
                        end
                end
                return true
        end

        # Check the conformity of a set of defined closures
        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
                var min_arity = 0
                for c in cs do
                        if not c.is_optional then min_arity += 1
                end
                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: 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..arity[ do
                                        var cdi = cd[i]
                                        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
                                if break_list != null then
                                        t = v.check_conform_multiexpr(t, break_list)
                                end
                        end
                else if arity != 0 then
                        v.error(self, "Error: {name} does not require blocks.")
                end
                return t
        end
end

redef class AAbsSendExpr
        # Compute the called global property
        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 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
                _return_type = rtype
        end

        private fun get_property(v: TypingVisitor, type_recv: MMType, is_implicit_self: Bool, name: Symbol): nullable MMMethod
        do
                if type_recv isa MMTypeNone then
                        v.error(self, "Error: Method '{name}' call on 'null'.")
                        return null
                end
                var lc = type_recv.local_class
                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 = lc.super_methods_named(name)
                        if props.length > 1 then
                                v.error(self, "Error: Ambigous method name '{name}' for {props.join(", ")}. Use explicit designation.")
                                return null
                        else if props.length == 1 then 
                                var p = lc[props.first.global]
                                assert p isa MMMethod
                                prop = p
                        end

                end
                if prop == null then
                        if is_implicit_self then
                                v.error(self, "Error: Method or variable '{name}' unknown in {type_recv}.")
                        else
                                v.error(self, "Error: Method '{name}' doesn't exists in {type_recv}.")
                        end
                        return null
                end
                return prop
        end

        # Get the signature for a local property and a receiver
        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)
                if not recv_is_self then psig = psig.not_for_self
                return psig
        end

        # The invoked method (once computed)
        redef fun prop do return _prop.as(not null)
        var _prop: nullable MMMethod

        # The return type (if any) (once computed)
        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
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: 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
                        v.explicit_other_init_call = true
                else if not order.has(cla) then
                        v.error(self, "Error: Constructor of class {cla} must be one in {order.join(", ")}.")
                else if cla == prev_class then
                        v.error(self, "Error: Only one super constructor invocation of class {cla} is allowed.")
                else
                        var last_is_found = prev_class == null
                        for c in order do
                                if c == prev_class then
                                        last_is_found = true
                                else if c == cla then
                                        if not last_is_found then
                                                v.error(self, "Error: Constructor of {c} must be invoked before constructor of {prev_class}")
                                        end
                                        esic.add(property)
                                        break
                                end
                        end
                end
        end

end

redef class ANewExpr
        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.local_class.global.is_abstract then
                        v.error(self, "Error: try to instantiate abstract class {t.local_class}.")
                        return
                end
                var name: Symbol
                if n_id == null then
                        name = once "init".to_symbol
                else
                        name = n_id.to_symbol
                end

                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.")
                        return
                end
                _stype = t
                _is_typed = true
        end
end


redef class ASendExpr
        # Name of the invoked property
        fun name: Symbol is abstract 

        # Closure definitions
        redef fun closure_defs: nullable Array[AClosureDef] do return null

        redef fun after_typing(v)
        do
                do_all_typing(v)
        end

        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
                var prop = _prop.as(not null)

                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.")
                        else if not n_expr.is_self then
                                v.error(self, "Error: constructor {prop} is not invoken on 'self'.")
                        else
                                register_super_init_call(v, prop)
                        end
                end

                _stype = return_type
                _is_typed = true
        end
end

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
                                v.error(self, "Error: try to invoke constructor {prop} in a method.")
                        else if not n_expr.is_self then
                                v.error(self, "Error: constructor {prop} is not invoken on 'self'.")
                        end
                end
                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

                var t2 = do_rvalue_typing(v, t)
                if t2 == null then return
                v.check_conform(self, t2, n_value.stype)

                _read_prop = prop
                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.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.")
                        else if not n_expr.is_self then
                                v.error(self, "Error: constructor {prop} is not invoken on 'self'.")
                        end
                end

                _is_typed = true
        end
end

redef class ABinopExpr
        redef fun compute_raw_arguments do return [n_expr2]
end
redef class AEqExpr
        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
                        if n_expr2.stype isa MMTypeNone then
                                v.warning(self, "Warning: comparaison between 2 null values.")
                        else
                                try_to_isa(v, n_expr2)
                        end
                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)
                        _if_true_variable_ctx = v.variable_ctx.sub_with(self, variable, v.type_none)
                end
        end
end
redef class ANeExpr
        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
                        if n_expr2.stype isa MMTypeNone then
                                v.warning(self, "Warning: comparaison between 2 null values.")
                        else
                                try_to_isa(v, n_expr2)
                        end
                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)
                        _if_false_variable_ctx = v.variable_ctx.sub_with(self, variable, v.type_none)
                end
        end
end
redef class ALtExpr
        redef fun name do return once "<".to_symbol
end
redef class ALeExpr
        redef fun name do return once "<=".to_symbol
end
redef class AGtExpr
        redef fun name do return once ">".to_symbol
end
redef class AGeExpr
        redef fun name do return once ">=".to_symbol
end
redef class APlusExpr
        redef fun name do return once "+".to_symbol
end
redef class AMinusExpr
        redef fun name do return once "-".to_symbol
end
redef class AStarshipExpr
        redef fun name do return once "<=>".to_symbol
end
redef class AStarExpr
        redef fun name do return once "*".to_symbol
end
redef class ASlashExpr
        redef fun name do return once "/".to_symbol
end
redef class APercentExpr
        redef fun name do return once "%".to_symbol
end

redef class AUminusExpr
        redef fun name do return once "unary -".to_symbol
        redef fun compute_raw_arguments do return null
end

redef class ACallFormExpr
        redef fun after_typing(v)
        do
                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
                                        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
                                        n = variable_create(variable)
                                        n._variable = variable
                                end
                                replace_with(n)
                                n.after_typing(v)
                                return
                        end
                end

                super
        end

        redef fun closure_defs
        do
                if n_closure_defs.is_empty then
                        return null
                else
                        return n_closure_defs.to_a
                end
        end

        # Create a variable acces corresponding to the call form
        fun variable_create(variable: Variable): AVarFormExpr is abstract
end

redef class ACallExpr
        redef fun variable_create(variable)
        do
                return new AVarExpr.init_avarexpr(n_id)
        end

        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 fun variable_create(variable)
        do
                return new AVarAssignExpr.init_avarassignexpr(n_id, n_assign, n_value)
        end

        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
        end
end

redef class ACallReassignExpr
        redef fun variable_create(variable)
        do
                return new AVarReassignExpr.init_avarreassignexpr(n_id, n_assign_op, n_value)
        end

        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 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 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
        end
end

redef class ABraReassignExpr
        redef fun name do return once "[]".to_symbol
        redef fun compute_raw_arguments do return n_args.to_a
end

redef class AInitExpr
        redef fun name do return once "init".to_symbol
        redef fun compute_raw_arguments do return n_args.to_a
end

redef class AClosureCallExpr
        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 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 not s then return
                _prop_signature = sig
                _stype = sig.return_type
                _is_typed = true
        end
end

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 var _escapable: nullable EscapableBlock

        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 fun accept_typing2(v: TypingVisitor, esc: EscapableClosure)
        do
                _escapable = esc

                var sig = esc.closure.signature
                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

                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_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)
                end

                _accept_typing2 = true
                accept_typing(v)

                if v.variable_ctx.unreash == false then
                        if closure.signature.return_type != null then
                                v.error(self, "Control error: Reached end of block (a 'continue' with a value was expected).")
                        else if closure.is_break and esc.break_list != null then
                                v.error(self, "Control error: Reached end of break block (a 'break' with a value was expected).")
                        end
                end
                v.variable_ctx = old_var_ctx
                v.base_variable_ctx = old_base_var_ctx
        end
end

class ATypeCheckExpr
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 isa MMTypeNone then
                        # ttype is not nullable because of prevous test
                        v.warning(self, "Warning: Expression is null therefore cannot be a {ttype}.")
                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 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)
                end
                _stype = v.type_bool
                _is_typed = true
        end
end

redef class AAsCastExpr
special ATypeCheckExpr
        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 fun after_typing(v)
        do
                if not n_expr.is_typed then return
                _is_typed = true
                if n_expr.is_statement then return
                _stype = n_expr.stype
        end
end

redef class AOnceExpr
        redef fun accept_typing(v)
        do
                if v.once_count > 0 then
                        v.warning(self, "Useless once in a once expression.")
                end
                v.once_count = v.once_count + 1

                super

                v.once_count = v.once_count - 1
        end
end