engines: move compilation of `abstract` method to MMethodDef

[nit.git] / src / interpreter / naive_interpreter.nit

# This file is part of NIT ( http://www.nitlanguage.org ).
#
# Copyright 2012 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.

# Interpretation of a Nit program directly on the AST
module naive_interpreter

import literal
import semantize
private import parser::tables
import mixin
import primitive_types

redef class ToolContext
        # --discover-call-trace
        var opt_discover_call_trace = new OptionBool("Trace calls of the first invocation of a method", "--discover-call-trace")

        redef init
        do
                super
                self.option_context.add_option(self.opt_discover_call_trace)
        end
end

redef class ModelBuilder
        # Execute the program from the entry point (`Sys::main`) of the `mainmodule`
        # `arguments` are the command-line arguments in order
        # REQUIRE that:
        #   1. the AST is fully loaded.
        #   2. the model is fully built.
        #   3. the instructions are fully analysed.
        fun run_naive_interpreter(mainmodule: MModule, arguments: Array[String])
        do
                var time0 = get_time
                self.toolcontext.info("*** START INTERPRETING ***", 1)

                var interpreter = new NaiveInterpreter(self, mainmodule, arguments)
                interpreter.start(mainmodule)

                var time1 = get_time
                self.toolcontext.info("*** END INTERPRETING: {time1-time0} ***", 2)
        end
end

# The visitor that interprets the Nit Program by walking on the AST
class NaiveInterpreter
        # The modelbuilder that know the AST and its associations with the model
        var modelbuilder: ModelBuilder

        # The main module of the program (used to lookup method)
        var mainmodule: MModule

        # The command line arguments of the interpreted program
        # arguments.first is the program name
        # arguments[1] is the first argument
        var arguments: Array[String]

        # The main Sys instance
        var mainobj: nullable Instance is noinit

        init
        do
                if mainmodule.model.get_mclasses_by_name("Bool") != null then
                        self.true_instance = new PrimitiveInstance[Bool](mainmodule.bool_type, true)
                        init_instance_primitive(self.true_instance)
                        self.false_instance = new PrimitiveInstance[Bool](mainmodule.bool_type, false)
                        init_instance_primitive(self.false_instance)
                end
                self.null_instance = new PrimitiveInstance[nullable Object](mainmodule.model.null_type, null)
        end

        # Starts the interpreter on the main module of a program
        fun start(mainmodule: MModule) do
                var interpreter = self
                var sys_type = mainmodule.sys_type
                if sys_type == null then return # no class Sys
                var mainobj = new MutableInstance(sys_type)
                interpreter.mainobj = mainobj
                interpreter.init_instance(mainobj)
                var initprop = mainmodule.try_get_primitive_method("init", sys_type.mclass)
                if initprop != null then
                        interpreter.send(initprop, [mainobj])
                end
                var mainprop = mainmodule.try_get_primitive_method("run", sys_type.mclass) or else
                        mainmodule.try_get_primitive_method("main", sys_type.mclass)
                if mainprop != null then
                        interpreter.send(mainprop, [mainobj])
                end
        end

        # Subtype test in the context of the mainmodule
        fun is_subtype(sub, sup: MType): Bool
        do
                return sub.is_subtype(self.mainmodule, current_receiver_class, sup)
        end

        # Get a primitive method in the context of the main module
        fun force_get_primitive_method(name: String, recv: MType): MMethod
        do
                assert recv isa MClassType
                return self.modelbuilder.force_get_primitive_method(current_node, name, recv.mclass, self.mainmodule)
        end

        # Is a return executed?
        # Set this mark to skip the evaluation until the end of the specified method frame
        var returnmark: nullable Frame = null

        # Is a break or a continue executed?
        # Set this mark to skip the evaluation until a labeled statement catch it with `is_escape`
        var escapemark: nullable EscapeMark = null

        # Is a return or a break or a continue executed?
        # Use this function to know if you must skip the evaluation of statements
        fun is_escaping: Bool do return returnmark != null or escapemark != null

        # The value associated with the current return/break/continue, if any.
        # Set the value when you set a escapemark.
        # Read the value when you catch a mark or reach the end of a method
        var escapevalue: nullable Instance = null

        # If there is a break/continue and is associated with `escapemark`, then return true and clear the mark.
        # If there is no break/continue or if `escapemark` is null then return false.
        # Use this function to catch a potential break/continue.
        fun is_escape(escapemark: nullable EscapeMark): Bool
        do
                if escapemark != null and self.escapemark == escapemark then
                        self.escapemark = null
                        return true
                else
                        return false
                end
        end

        # Evaluate `n` as an expression in the current context.
        # Return the value of the expression.
        # If `n` cannot be evaluated, then aborts.
        fun expr(n: AExpr): nullable Instance
        do
                var frame = self.frame
                var old = frame.current_node
                frame.current_node = n
                #n.debug("IN Execute expr")
                var i = n.expr(self)
                if i == null and not self.is_escaping then
                        n.debug("inconsitance: no value and not escaping.")
                end
                var implicit_cast_to = n.implicit_cast_to
                if implicit_cast_to != null then
                        var mtype = self.unanchor_type(implicit_cast_to)
                        if not self.is_subtype(i.mtype, mtype) then n.fatal(self, "Cast failed. Expected `{implicit_cast_to}`, got `{i.mtype}`")
                end

                #n.debug("OUT Execute expr: value is {i}")
                #if not is_subtype(i.mtype, n.mtype.as(not null)) then n.debug("Expected {n.mtype.as(not null)} got {i}")
                frame.current_node = old
                return i
        end

        # Evaluate `n` as a statement in the current context.
        # Do nothing if `n` is null.
        # If `n` cannot be evaluated, then aborts.
        fun stmt(n: nullable AExpr)
        do
                if n == null then return

                if n.comprehension != null then
                        var comprehension = frame.comprehension.as(not null)
                        var i = expr(n)
                        if i != null then comprehension.add(i)
                        return
                end

                var frame = self.frame
                var old = frame.current_node
                frame.current_node = n
                n.stmt(self)
                frame.current_node = old
        end

        # Map used to store values of nodes that must be evaluated once in the system (`AOnceExpr`)
        var onces: Map[ANode, Instance] = new HashMap[ANode, Instance]

        # Return the boolean instance associated with `val`.
        fun bool_instance(val: Bool): Instance
        do
                if val then return self.true_instance else return self.false_instance
        end

        # Return the integer instance associated with `val`.
        fun int_instance(val: Int): Instance
        do
                var ic = get_primitive_class("Int")
                var instance = new PrimitiveInstance[Int](ic.mclass_type, val)
                init_instance_primitive(instance)
                return instance
        end

        # Return the char instance associated with `val`.
        fun char_instance(val: Char): Instance
        do
                var ic = get_primitive_class("Char")
                var instance = new PrimitiveInstance[Char](ic.mclass_type, val)
                init_instance_primitive(instance)
                return instance
        end

        # Return the float instance associated with `val`.
        fun float_instance(val: Float): Instance
        do
                var ic = get_primitive_class("Float")
                var instance = new PrimitiveInstance[Float](ic.mclass_type, val)
                init_instance_primitive(instance)
                return instance
        end

        # The unique instance of the `true` value.
        var true_instance: Instance is noinit

        # The unique instance of the `false` value.
        var false_instance: Instance is noinit

        # The unique instance of the `null` value.
        var null_instance: Instance is noinit

        # Return a new array made of `values`.
        # The dynamic type of the result is Array[elttype].
        fun array_instance(values: Array[Instance], elttype: MType): Instance
        do
                assert not elttype.need_anchor
                var nat = new PrimitiveInstance[Array[Instance]](get_primitive_class("NativeArray").get_mtype([elttype]), values)
                init_instance_primitive(nat)
                var mtype = get_primitive_class("Array").get_mtype([elttype])
                var res = new MutableInstance(mtype)
                self.init_instance(res)
                self.send(self.force_get_primitive_method("with_native", mtype), [res, nat, self.int_instance(values.length)])
                return res
        end

        # Return a instance associated to a primitive class
        # Current primitive classes are `Int`, `Bool`, and `String`
        fun value_instance(object: Object): Instance
        do
                if object isa Int then
                        return int_instance(object)
                else if object isa Bool then
                        return bool_instance(object)
                else if object isa String then
                        return string_instance(object)
                else
                        abort
                end
        end

        # Return a new native string initialized with `txt`
        fun native_string_instance(txt: String): Instance
        do
                var val = new FlatBuffer.from(txt)
                val.add('\0')
                var ic = get_primitive_class("NativeString")
                var instance = new PrimitiveInstance[Buffer](ic.mclass_type, val)
                init_instance_primitive(instance)
                return instance
        end

        # Return a new String instance for `txt`
        fun string_instance(txt: String): Instance
        do
                var nat = native_string_instance(txt)
                var res = self.send(self.force_get_primitive_method("to_s_with_length", nat.mtype), [nat, self.int_instance(txt.length)])
                assert res != null
                return res
        end

        # The current frame used to store local variables of the current method executed
        fun frame: Frame do return frames.first

        # The stack of all frames. The first one is the current one.
        var frames = new List[Frame]

        # Return a stack trace. One line per function
        fun stack_trace: String
        do
                var b = new FlatBuffer
                b.append(",---- Stack trace -- - -  -\n")
                for f in frames do
                        b.append("| {f.mpropdef} ({f.current_node.location})\n")
                end
                b.append("`------------------- - -  -")
                return b.to_s
        end

        # The current node, used to print errors, debug and stack-traces
        fun current_node: nullable ANode
        do
                if frames.is_empty then return null
                return frames.first.current_node
        end

        # The dynamic type of the current `self`
        fun current_receiver_class: MClassType
        do
                return frames.first.arguments.first.mtype.as(MClassType)
        end

        # Exit the program with a message
        fun fatal(message: String)
        do
                var node = current_node
                if node == null then
                        print message
                else
                        node.fatal(self, message)
                end
                exit(1)
        end

        # Debug on the current node
        fun debug(message: String)
        do
                var node = current_node
                if node == null then
                        print message
                else
                        node.debug(message)
                end
        end

        # Retrieve the value of the variable in the current frame
        fun read_variable(v: Variable): Instance
        do
                var f = frames.first
                return f.map[v]
        end

        # Assign the value of the variable in the current frame
        fun write_variable(v: Variable, value: Instance)
        do
                var f = frames.first
                f.map[v] = value
        end

        # Store known methods, used to trace methods as they are reached
        var discover_call_trace: Set[MMethodDef] = new HashSet[MMethodDef]

        # Evaluate `args` as expressions in the call of `mpropdef` on `recv`.
        # This method is used to manage varargs in signatures and returns the real array
        # of instances to use in the call.
        # Return `null` if one of the evaluation of the arguments return null.
        fun varargize(mpropdef: MMethodDef, recv: Instance, args: SequenceRead[AExpr]): nullable Array[Instance]
        do
                var msignature = mpropdef.new_msignature or else mpropdef.msignature.as(not null)
                var res = new Array[Instance]
                res.add(recv)

                if args.is_empty then return res

                var vararg_rank = msignature.vararg_rank
                var vararg_len = args.length - msignature.arity
                if vararg_len < 0 then vararg_len = 0

                for i in [0..msignature.arity[ do
                        if i == vararg_rank then
                                var ne = args[i]
                                if ne isa AVarargExpr then
                                        var e = self.expr(ne.n_expr)
                                        if e == null then return null
                                        res.add(e)
                                        continue
                                end
                                var vararg = new Array[Instance]
                                for j in [vararg_rank..vararg_rank+vararg_len] do
                                        var e = self.expr(args[j])
                                        if e == null then return null
                                        vararg.add(e)
                                end
                                var elttype = msignature.mparameters[vararg_rank].mtype.anchor_to(self.mainmodule, recv.mtype.as(MClassType))
                                res.add(self.array_instance(vararg, elttype))
                        else
                                var j = i
                                if i > vararg_rank then j += vararg_len
                                var e = self.expr(args[j])
                                if e == null then return null
                                res.add(e)
                        end
                end
                return res
        end

        # Execute `mpropdef` for a `args` (where `args[0]` is the receiver).
        # Return a value if `mpropdef` is a function, or null if it is a procedure.
        # The call is direct/static. There is no message-sending/late-binding.
        fun call(mpropdef: MMethodDef, args: Array[Instance]): nullable Instance
        do
                if self.modelbuilder.toolcontext.opt_discover_call_trace.value and not self.discover_call_trace.has(mpropdef) then
                        self.discover_call_trace.add mpropdef
                        self.debug("Discovered {mpropdef}")
                end
                assert args.length == mpropdef.msignature.arity + 1 else debug("Invalid arity for {mpropdef}. {args.length} arguments given.")

                # Look for the AST node that implements the property
                var val = mpropdef.constant_value

                var node = modelbuilder.mpropdef2node(mpropdef)
                if mpropdef.is_abstract then
                        if node != null then
                                self.frames.unshift new Frame(node, mpropdef, args)
                        end
                        fatal("Abstract method `{mpropdef.mproperty.name}` called on `{args.first.mtype}`")
                        abort
                end

                if node isa APropdef then
                        self.parameter_check(node, mpropdef, args)
                        return node.call(self, mpropdef, args)
                else if node isa AClassdef then
                        self.parameter_check(node, mpropdef, args)
                        return node.call(self, mpropdef, args)
                else if node != null then
                        fatal("Fatal Error: method {mpropdef} associated to unexpected AST node {node.location}")
                        abort
                else if val != null then
                        return value_instance(val)
                else
                        fatal("Fatal Error: method {mpropdef} not found in the AST")
                        abort
                end
        end

        # Execute type checks of covariant parameters
        fun parameter_check(node: ANode, mpropdef: MMethodDef, args: Array[Instance])
        do
                var msignature = mpropdef.msignature
                for i in [0..msignature.arity[ do
                        # skip test for vararg since the array is instantiated with the correct polymorphic type
                        if msignature.vararg_rank == i then continue

                        # skip if the cast is not required
                        var origmtype =  mpropdef.mproperty.intro.msignature.mparameters[i].mtype
                        if not origmtype.need_anchor then continue

                        #print "{mpropdef}: {mpropdef.mproperty.intro.msignature.mparameters[i]}"

                        # get the parameter type
                        var mtype = msignature.mparameters[i].mtype
                        var anchor = args.first.mtype.as(MClassType)
                        var amtype = mtype.anchor_to(self.mainmodule, anchor)
                        if not args[i+1].mtype.is_subtype(self.mainmodule, anchor, amtype) then
                                node.fatal(self, "Cast failed. Expected `{mtype}`, got `{args[i+1].mtype}`")
                        end
                end
        end

        # Common code for runtime injected calls and normal calls
        fun send_commons(mproperty: MMethod, args: Array[Instance], mtype: MType): nullable Instance
        do
                if mtype isa MNullType then
                        if mproperty.name == "==" or mproperty.name == "is_same_instance" then
                                return self.bool_instance(args[0] == args[1])
                        else if mproperty.name == "!=" then
                                return self.bool_instance(args[0] != args[1])
                        end
                        #fatal("Receiver is null. {mproperty}. {args.join(" ")} {self.frame.current_node.class_name}")
                        fatal("Receiver is null")
                end
                return null
        end

        # Execute a full `callsite` for given `args`
        # Use this method, instead of `send` to execute and control the additional behavior of the call-sites
        fun callsite(callsite: nullable CallSite, arguments: Array[Instance]): nullable Instance
        do
                var initializers = callsite.mpropdef.initializers
                if not initializers.is_empty then
                        var recv = arguments.first
                        var i = 1
                        for p in initializers do
                                if p isa MMethod then
                                        var args = [recv]
                                        for x in p.intro.msignature.mparameters do
                                                args.add arguments[i]
                                                i += 1
                                        end
                                        self.send(p, args)
                                else if p isa MAttribute then
                                        assert recv isa MutableInstance
                                        write_attribute(p, recv, arguments[i])
                                        i += 1
                                else abort
                        end
                        assert i == arguments.length

                        return send(callsite.mproperty, [recv])
                end
                return send(callsite.mproperty, arguments)
        end

        # Execute `mproperty` for a `args` (where `args[0]` is the receiver).
        # Return a value if `mproperty` is a function, or null if it is a procedure.
        # The call is polymorphic. There is a message-sending/late-binding according to the receiver (args[0]).
        fun send(mproperty: MMethod, args: Array[Instance]): nullable Instance
        do
                var recv = args.first
                var mtype = recv.mtype
                var ret = send_commons(mproperty, args, mtype)
                if ret != null then return ret
                var propdef = mproperty.lookup_first_definition(self.mainmodule, mtype)
                return self.call(propdef, args)
        end

        # Read the attribute `mproperty` of an instance `recv` and return its value.
        # If the attribute in not yet initialized, then aborts with an error message.
        fun read_attribute(mproperty: MAttribute, recv: Instance): Instance
        do
                assert recv isa MutableInstance
                if not recv.attributes.has_key(mproperty) then
                        fatal("Uninitialized attribute {mproperty.name}")
                        abort
                end
                return recv.attributes[mproperty]
        end

        # Replace in `recv` the value of the attribute `mproperty` by `value`
        fun write_attribute(mproperty: MAttribute, recv: Instance, value: Instance)
        do
                assert recv isa MutableInstance
                recv.attributes[mproperty] = value
        end

        # Is the attribute `mproperty` initialized the instance `recv`?
        fun isset_attribute(mproperty: MAttribute, recv: Instance): Bool
        do
                assert recv isa MutableInstance
                return recv.attributes.has_key(mproperty)
        end

        # Collect attributes of a type in the order of their init
        fun collect_attr_propdef(mtype: MType): Array[AAttrPropdef]
        do
                var cache = self.collect_attr_propdef_cache
                if cache.has_key(mtype) then return cache[mtype]

                var res = new Array[AAttrPropdef]
                var cds = mtype.collect_mclassdefs(self.mainmodule).to_a
                self.mainmodule.linearize_mclassdefs(cds)
                for cd in cds do
                        res.add_all(modelbuilder.collect_attr_propdef(cd))
                end

                cache[mtype] = res
                return res
        end

        private var collect_attr_propdef_cache = new HashMap[MType, Array[AAttrPropdef]]

        # Fill the initial values of the newly created instance `recv`.
        # `recv.mtype` is used to know what must be filled.
        fun init_instance(recv: Instance)
        do
                for npropdef in collect_attr_propdef(recv.mtype) do
                        npropdef.init_expr(self, recv)
                end
        end

        # A hook to initialize a `PrimitiveInstance`
        fun init_instance_primitive(recv: Instance) do end

        # Return the primitive `MClass` corresponding to the `name` given in parameter
        # `name` : name of the primitive class
        fun get_primitive_class(name: String): MClass
        do
                return mainmodule.get_primitive_class(name)
        end

        # This function determines the correct type according to the receiver of the current propdef (self).
        fun unanchor_type(mtype: MType): MType
        do
                return mtype.anchor_to(self.mainmodule, current_receiver_class)
        end

        # Placebo instance used to mark internal error result when `null` already have a meaning.
        # TODO: replace with multiple return or something better
        var error_instance = new MutableInstance(modelbuilder.model.null_type) is lazy
end

# An instance represents a value of the executed program.
abstract class Instance
        # The dynamic type of the instance
        # ASSERT: not self.mtype.is_anchored
        var mtype: MType

        # return true if the instance is the true value.
        # return false if the instance is the true value.
        # else aborts
        fun is_true: Bool do abort

        # Return true if `self` IS `o` (using the Nit semantic of is)
        fun eq_is(o: Instance): Bool do return self.is_same_instance(o)

        # Human readable object identity "Type#number"
        redef fun to_s do return "{mtype}"

        # Return the integer value if the instance is an integer.
        # else aborts
        fun to_i: Int do abort

        # Return the integer value if the instance is a float.
        # else aborts
        fun to_f: Float do abort

        # The real value encapsulated if the instance is primitive.
        # Else aborts.
        fun val: nullable Object do abort
end

# A instance with attribute (standards objects)
class MutableInstance
        super Instance

        # The values of the attributes
        var attributes: Map[MAttribute, Instance] = new HashMap[MAttribute, Instance]
end

# Special instance to handle primitives values (int, bool, etc.)
# The trick it just to encapsulate the <<real>> value
class PrimitiveInstance[E]
        super Instance

        # The real value encapsulated
        redef var val: E

        redef fun is_true
        do
                if val == true then return true
                if val == false then return false
                abort
        end

        redef fun ==(o)
        do
                if not o isa PrimitiveInstance[nullable Object] then return false
                return self.val == o.val
        end

        redef fun eq_is(o)
        do
                if not o isa PrimitiveInstance[nullable Object] then return false
                return self.val.is_same_instance(o.val)
        end

        redef fun to_s do return "{mtype}#{val.object_id}({val or else "null"})"

        redef fun to_i do return val.as(Int)

        redef fun to_f do return val.as(Float)
end

# Information about local variables in a running method
class Frame
        # The current visited node
        # The node is stored by frame to keep a stack trace
        var current_node: ANode
        # The executed property.
        # A Method in case of a call, an attribute in case of a default initialization.
        var mpropdef: MPropDef
        # Arguments of the method (the first is the receiver)
        var arguments: Array[Instance]
        # Mapping between a variable and the current value
        private var map: Map[Variable, Instance] = new HashMap[Variable, Instance]
        var comprehension: nullable Array[Instance] = null
end

redef class ANode
        # Aborts the program with a message
        # `v` is used to know if a colored message is displayed or not
        fun fatal(v: NaiveInterpreter, message: String)
        do
                if v.modelbuilder.toolcontext.opt_no_color.value == true then
                        sys.stderr.write("Runtime error: {message} ({location.file.filename}:{location.line_start})\n")
                else
                        sys.stderr.write("{location}: Runtime error: {message}\n{location.colored_line("0;31")}\n")
                        sys.stderr.write(v.stack_trace)
                        sys.stderr.write("\n")
                end
                exit(1)
        end
end

redef class APropdef
        # Execute a `mpropdef` associated with the current node.
        private fun call(v: NaiveInterpreter, mpropdef: MMethodDef, args: Array[Instance]): nullable Instance
        do
                fatal(v, "NOT YET IMPLEMENTED method kind {class_name}. {mpropdef}")
                abort
        end
end

redef class AMethPropdef
        super TablesCapable

        redef fun call(v, mpropdef, args)
        do
                var f = new Frame(self, self.mpropdef.as(not null), args)
                var res = call_commons(v, mpropdef, args, f)
                v.frames.shift
                if v.returnmark == f then
                        v.returnmark = null
                        res = v.escapevalue
                        v.escapevalue = null
                        return res
                end
                return res
        end

        private fun call_commons(v: NaiveInterpreter, mpropdef: MMethodDef, arguments: Array[Instance], f: Frame): nullable Instance
        do
                v.frames.unshift(f)

                for i in [0..mpropdef.msignature.arity[ do
                        var variable = self.n_signature.n_params[i].variable
                        assert variable != null
                        v.write_variable(variable, arguments[i+1])
                end

                # Call the implicit super-init
                var auto_super_inits = self.auto_super_inits
                if auto_super_inits != null then
                        var args = [arguments.first]
                        for auto_super_init in auto_super_inits do
                                args.clear
                                for i in [0..auto_super_init.msignature.arity+1[ do
                                        args.add(arguments[i])
                                end
                                assert auto_super_init.mproperty != mpropdef.mproperty
                                v.callsite(auto_super_init, args)
                        end
                end
                if auto_super_call then
                        # standard call-next-method
                        var superpd = mpropdef.lookup_next_definition(v.mainmodule, arguments.first.mtype)
                        v.call(superpd, arguments)
                end

                if mpropdef.is_intern or mpropdef.is_extern then
                        var res = intern_call(v, mpropdef, arguments)
                        if res != v.error_instance then return res
                end

                if n_block != null then
                        v.stmt(self.n_block)
                        return null
                end

                if mpropdef.is_intern then
                        fatal(v, "NOT YET IMPLEMENTED intern {mpropdef}")
                else if mpropdef.is_extern then
                        fatal(v, "NOT YET IMPLEMENTED extern {mpropdef}")
                else
                        fatal(v, "NOT YET IMPLEMENTED <wat?> {mpropdef}")
                end
                abort
        end

        # Interprets a intern or a shortcut extern method.
        # Returns the result for a function, `null` for a procedure, or `error_instance` if the method is unknown.
        private fun intern_call(v: NaiveInterpreter, mpropdef: MMethodDef, args: Array[Instance]): nullable Instance
        do
                var pname = mpropdef.mproperty.name
                var cname = mpropdef.mclassdef.mclass.name
                if pname == "output" then
                        var recv = args.first
                        recv.val.output
                        return null
                else if pname == "object_id" then
                        var recv = args.first
                        if recv isa PrimitiveInstance[Object] then
                                return v.int_instance(recv.val.object_id)
                        else
                                return v.int_instance(recv.object_id)
                        end
                else if pname == "output_class_name" then
                        var recv = args.first
                        print recv.mtype
                        return null
                else if pname == "native_class_name" then
                        var recv = args.first
                        var txt = recv.mtype.to_s
                        return v.native_string_instance(txt)
                else if pname == "==" then
                        # == is correctly redefined for instances
                        return v.bool_instance(args[0] == args[1])
                else if pname == "!=" then
                        return v.bool_instance(args[0] != args[1])
                else if pname == "is_same_type" then
                        return v.bool_instance(args[0].mtype == args[1].mtype)
                else if pname == "is_same_instance" then
                        return v.bool_instance(args[0].eq_is(args[1]))
                else if pname == "exit" then
                        exit(args[1].to_i)
                        abort
                else if pname == "buffer_mode_full" then
                        return v.int_instance(sys.buffer_mode_full)
                else if pname == "buffer_mode_line" then
                        return v.int_instance(sys.buffer_mode_line)
                else if pname == "buffer_mode_none" then
                        return v.int_instance(sys.buffer_mode_none)
                else if pname == "sys" then
                        return v.mainobj
                else if cname == "Int" then
                        var recvval = args[0].to_i
                        if pname == "unary -" then
                                return v.int_instance(-args[0].to_i)
                        else if pname == "+" then
                                return v.int_instance(args[0].to_i + args[1].to_i)
                        else if pname == "-" then
                                return v.int_instance(args[0].to_i - args[1].to_i)
                        else if pname == "*" then
                                return v.int_instance(args[0].to_i * args[1].to_i)
                        else if pname == "%" then
                                return v.int_instance(args[0].to_i % args[1].to_i)
                        else if pname == "/" then
                                return v.int_instance(args[0].to_i / args[1].to_i)
                        else if pname == "<" then
                                return v.bool_instance(args[0].to_i < args[1].to_i)
                        else if pname == ">" then
                                return v.bool_instance(args[0].to_i > args[1].to_i)
                        else if pname == "<=" then
                                return v.bool_instance(args[0].to_i <= args[1].to_i)
                        else if pname == ">=" then
                                return v.bool_instance(args[0].to_i >= args[1].to_i)
                        else if pname == "<=>" then
                                return v.int_instance(args[0].to_i <=> args[1].to_i)
                        else if pname == "ascii" then
                                return v.char_instance(args[0].to_i.ascii)
                        else if pname == "to_f" then
                                return v.float_instance(args[0].to_i.to_f)
                        else if pname == "lshift" then
                                return v.int_instance(args[0].to_i.lshift(args[1].to_i))
                        else if pname == "rshift" then
                                return v.int_instance(args[0].to_i.rshift(args[1].to_i))
                        else if pname == "rand" then
                                var res = recvval.rand
                                return v.int_instance(res)
                        else if pname == "bin_and" then
                                return v.int_instance(args[0].to_i.bin_and(args[1].to_i))
                        else if pname == "bin_or" then
                                return v.int_instance(args[0].to_i.bin_or(args[1].to_i))
                        else if pname == "bin_xor" then
                                return v.int_instance(args[0].to_i.bin_xor(args[1].to_i))
                        else if pname == "bin_not" then
                                return v.int_instance(args[0].to_i.bin_not)
                        else if pname == "int_to_s_len" then
                                return v.int_instance(recvval.to_s.length)
                        else if pname == "native_int_to_s" then
                                var s = recvval.to_s
                                var srecv = args[1].val.as(Buffer)
                                srecv.clear
                                srecv.append(s)
                                srecv.add('\0')
                                return null
                        else if pname == "strerror_ext" then
                                return v.native_string_instance(recvval.strerror)
                        end
                else if cname == "Char" then
                        var recv = args[0].val.as(Char)
                        if pname == "ascii" then
                                return v.int_instance(recv.ascii)
                        else if pname == "successor" then
                                return v.char_instance(recv.successor(args[1].to_i))
                        else if pname == "predecessor" then
                                return v.char_instance(recv.predecessor(args[1].to_i))
                        else if pname == "<" then
                                return v.bool_instance(recv < args[1].val.as(Char))
                        else if pname == ">" then
                                return v.bool_instance(recv > args[1].val.as(Char))
                        else if pname == "<=" then
                                return v.bool_instance(recv <= args[1].val.as(Char))
                        else if pname == ">=" then
                                return v.bool_instance(recv >= args[1].val.as(Char))
                        else if pname == "<=>" then
                                return v.int_instance(recv <=> args[1].val.as(Char))
                        end
                else if cname == "Float" then
                        var recv = args[0].to_f
                        if pname == "unary -" then
                                return v.float_instance(-recv)
                        else if pname == "+" then
                                return v.float_instance(recv + args[1].to_f)
                        else if pname == "-" then
                                return v.float_instance(recv - args[1].to_f)
                        else if pname == "*" then
                                return v.float_instance(recv * args[1].to_f)
                        else if pname == "/" then
                                return v.float_instance(recv / args[1].to_f)
                        else if pname == "<" then
                                return v.bool_instance(recv < args[1].to_f)
                        else if pname == ">" then
                                return v.bool_instance(recv > args[1].to_f)
                        else if pname == "<=" then
                                return v.bool_instance(recv <= args[1].to_f)
                        else if pname == ">=" then
                                return v.bool_instance(recv >= args[1].to_f)
                        else if pname == "to_i" then
                                return v.int_instance(recv.to_i)
                        else if pname == "cos" then
                                return v.float_instance(args[0].to_f.cos)
                        else if pname == "sin" then
                                return v.float_instance(args[0].to_f.sin)
                        else if pname == "tan" then
                                return v.float_instance(args[0].to_f.tan)
                        else if pname == "acos" then
                                return v.float_instance(args[0].to_f.acos)
                        else if pname == "asin" then
                                return v.float_instance(args[0].to_f.asin)
                        else if pname == "atan" then
                                return v.float_instance(args[0].to_f.atan)
                        else if pname == "sqrt" then
                                return v.float_instance(args[0].to_f.sqrt)
                        else if pname == "exp" then
                                return v.float_instance(args[0].to_f.exp)
                        else if pname == "log" then
                                return v.float_instance(args[0].to_f.log)
                        else if pname == "pow" then
                                return v.float_instance(args[0].to_f.pow(args[1].to_f))
                        else if pname == "rand" then
                                return v.float_instance(args[0].to_f.rand)
                        else if pname == "abs" then
                                return v.float_instance(args[0].to_f.abs)
                        else if pname == "hypot_with" then
                                return v.float_instance(args[0].to_f.hypot_with(args[1].to_f))
                        else if pname == "is_nan" then
                                return v.bool_instance(args[0].to_f.is_nan)
                        else if pname == "is_inf_extern" then
                                return v.bool_instance(args[0].to_f.is_inf != 0)
                        else if pname == "round" then
                                return v.float_instance(args[0].to_f.round)
                        end
                else if cname == "NativeString" then
                        if pname == "new" then
                                return v.native_string_instance("!" * args[1].to_i)
                        end
                        var recvval = args.first.val.as(Buffer)
                        if pname == "[]" then
                                var arg1 = args[1].to_i
                                if arg1 >= recvval.length or arg1 < 0 then
                                        debug("Illegal access on {recvval} for element {arg1}/{recvval.length}")
                                end
                                return v.char_instance(recvval.chars[arg1])
                        else if pname == "[]=" then
                                var arg1 = args[1].to_i
                                if arg1 >= recvval.length or arg1 < 0 then
                                        debug("Illegal access on {recvval} for element {arg1}/{recvval.length}")
                                end
                                recvval.chars[arg1] = args[2].val.as(Char)
                                return null
                        else if pname == "copy_to" then
                                # sig= copy_to(dest: NativeString, length: Int, from: Int, to: Int)
                                var destval = args[1].val.as(FlatBuffer)
                                var lenval = args[2].to_i
                                var fromval = args[3].to_i
                                var toval = args[4].to_i
                                if fromval < 0 then
                                        debug("Illegal access on {recvval} for element {fromval}/{recvval.length}")
                                end
                                if fromval + lenval > recvval.length then
                                        debug("Illegal access on {recvval} for element {fromval}+{lenval}/{recvval.length}")
                                end
                                if toval < 0 then
                                        debug("Illegal access on {destval} for element {toval}/{destval.length}")
                                end
                                if toval + lenval > destval.length then
                                        debug("Illegal access on {destval} for element {toval}+{lenval}/{destval.length}")
                                end
                                recvval.as(FlatBuffer).copy(fromval, lenval, destval, toval)
                                return null
                        else if pname == "atoi" then
                                return v.int_instance(recvval.to_i)
                        else if pname == "file_exists" then
                                return v.bool_instance(recvval.to_s.file_exists)
                        else if pname == "file_mkdir" then
                                recvval.to_s.mkdir
                                return null
                        else if pname == "file_chdir" then
                                recvval.to_s.chdir
                                return null
                        else if pname == "file_realpath" then
                                return v.native_string_instance(recvval.to_s.realpath)
                        else if pname == "get_environ" then
                                var txt = recvval.to_s.environ
                                return v.native_string_instance(txt)
                        else if pname == "system" then
                                var res = sys.system(recvval.to_s)
                                return v.int_instance(res)
                        else if pname == "atof" then
                                return v.float_instance(recvval.to_f)
                        end
                else if cname == "String" then
                        var cs = v.send(v.force_get_primitive_method("to_cstring", args.first.mtype), [args.first])
                        var str = cs.val.to_s
                        if pname == "files" then
                                var res = new Array[Instance]
                                for f in str.files do res.add v.string_instance(f)
                                return v.array_instance(res, v.get_primitive_class("String").mclass_type)
                        end
                else if pname == "calloc_string" then
                        return v.native_string_instance("!" * args[1].to_i)
                else if cname == "NativeArray" then
                        if pname == "new" then
                                var val = new Array[Instance].filled_with(v.null_instance, args[1].to_i)
                                var instance = new PrimitiveInstance[Array[Instance]](args[0].mtype, val)
                                v.init_instance_primitive(instance)
                                return instance
                        end
                        var recvval = args.first.val.as(Array[Instance])
                        if pname == "[]" then
                                if args[1].to_i >= recvval.length or args[1].to_i < 0 then
                                        debug("Illegal access on {recvval} for element {args[1].to_i}/{recvval.length}")
                                end
                                return recvval[args[1].to_i]
                        else if pname == "[]=" then
                                recvval[args[1].to_i] = args[2]
                                return null
                        else if pname == "length" then
                                return v.int_instance(recvval.length)
                        else if pname == "copy_to" then
                                recvval.copy_to(0, args[2].to_i, args[1].val.as(Array[Instance]), 0)
                                return null
                        end
                else if cname == "NativeFile" then
                        if pname == "native_stdout" then
                                var inst = new PrimitiveNativeFile.native_stdout
                                var instance = new PrimitiveInstance[PrimitiveNativeFile](mpropdef.mclassdef.mclass.mclass_type, inst)
                                v.init_instance_primitive(instance)
                                return instance
                        else if pname == "native_stdin" then
                                var inst = new PrimitiveNativeFile.native_stdin
                                var instance = new PrimitiveInstance[PrimitiveNativeFile](mpropdef.mclassdef.mclass.mclass_type, inst)
                                v.init_instance_primitive(instance)
                                return instance
                        else if pname == "native_stderr" then
                                var inst = new PrimitiveNativeFile.native_stderr
                                var instance = new PrimitiveInstance[PrimitiveNativeFile](mpropdef.mclassdef.mclass.mclass_type, inst)
                                v.init_instance_primitive(instance)
                                return instance
                        else if pname == "io_open_read" then
                                var a1 = args[1].val.as(Buffer)
                                var inst = new PrimitiveNativeFile.io_open_read(a1.to_s)
                                var instance = new PrimitiveInstance[PrimitiveNativeFile](mpropdef.mclassdef.mclass.mclass_type, inst)
                                v.init_instance_primitive(instance)
                                return instance
                        else if pname == "io_open_write" then
                                var a1 = args[1].val.as(Buffer)
                                var inst = new PrimitiveNativeFile.io_open_write(a1.to_s)
                                var instance = new PrimitiveInstance[PrimitiveNativeFile](mpropdef.mclassdef.mclass.mclass_type, inst)
                                v.init_instance_primitive(instance)
                                return instance
                        end
                        var recvval = args.first.val
                        if pname == "io_write" then
                                var a1 = args[1].val.as(Buffer)
                                return v.int_instance(recvval.as(PrimitiveNativeFile).io_write(a1.to_cstring, args[2].to_i))
                        else if pname == "io_read" then
                                var a1 = args[1].val.as(Buffer)
                                var ns = new NativeString(a1.length)
                                var len = recvval.as(PrimitiveNativeFile).io_read(ns, args[2].to_i)
                                a1.clear
                                a1.append(ns.to_s_with_length(len))
                                return v.int_instance(len)
                        else if pname == "flush" then
                                recvval.as(PrimitiveNativeFile).flush
                                return null
                        else if pname == "io_close" then
                                return v.int_instance(recvval.as(PrimitiveNativeFile).io_close)
                        else if pname == "set_buffering_type" then
                                return v.int_instance(recvval.as(PrimitiveNativeFile).set_buffering_type(args[1].to_i, args[2].to_i))
                        end
                else if pname == "calloc_array" then
                        var recvtype = args.first.mtype.as(MClassType)
                        var mtype: MType
                        mtype = recvtype.supertype_to(v.mainmodule, recvtype, v.get_primitive_class("ArrayCapable"))
                        mtype = mtype.arguments.first
                        var val = new Array[Instance].filled_with(v.null_instance, args[1].to_i)
                        var instance = new PrimitiveInstance[Array[Instance]](v.get_primitive_class("NativeArray").get_mtype([mtype]), val)
                        v.init_instance_primitive(instance)
                        return instance
                else if pname == "native_argc" then
                        return v.int_instance(v.arguments.length)
                else if pname == "native_argv" then
                        var txt = v.arguments[args[1].to_i]
                        return v.native_string_instance(txt)
                else if pname == "native_argc" then
                        return v.int_instance(v.arguments.length)
                else if pname == "native_argv" then
                        var txt = v.arguments[args[1].to_i]
                        return v.native_string_instance(txt)
                else if pname == "get_time" then
                        return v.int_instance(get_time)
                else if pname == "srand" then
                        srand
                        return null
                else if pname == "srand_from" then
                        srand_from(args[1].to_i)
                        return null
                else if pname == "atan2" then
                        return v.float_instance(atan2(args[1].to_f, args[2].to_f))
                else if pname == "pi" then
                        return v.float_instance(pi)
                else if pname == "lexer_goto" then
                        return v.int_instance(lexer_goto(args[1].to_i, args[2].to_i))
                else if pname == "lexer_accept" then
                        return v.int_instance(lexer_accept(args[1].to_i))
                else if pname == "parser_goto" then
                        return v.int_instance(parser_goto(args[1].to_i, args[2].to_i))
                else if pname == "parser_action" then
                        return v.int_instance(parser_action(args[1].to_i, args[2].to_i))
                else if pname == "file_getcwd" then
                        return v.native_string_instance(getcwd)
                else if pname == "errno" then
                        return v.int_instance(sys.errno)
                else if pname == "address_is_null" then
                        var recv = args[0]
                        if recv isa PrimitiveInstance[PrimitiveNativeFile] then
                                return v.bool_instance(recv.val.address_is_null)
                        end
                        return v.false_instance
                end
                return v.error_instance
        end
end

redef class AAttrPropdef
        redef fun call(v, mpropdef, args)
        do
                var recv = args.first
                assert recv isa MutableInstance
                var attr = self.mpropdef.mproperty
                if mpropdef == mreadpropdef then
                        assert args.length == 1
                        if not is_lazy or v.isset_attribute(attr, recv) then return v.read_attribute(attr, recv)
                        return evaluate_expr(v, recv)
                else if mpropdef == mwritepropdef then
                        assert args.length == 2
                        v.write_attribute(attr, recv, args[1])
                        return null
                else
                        abort
                end
        end

        # Evaluate and set the default value of the attribute in `recv`
        private fun init_expr(v: NaiveInterpreter, recv: Instance)
        do
                if is_lazy then return
                if has_value then
                        evaluate_expr(v, recv)
                        return
                end
                var mtype = self.mpropdef.static_mtype.as(not null)
                mtype = mtype.anchor_to(v.mainmodule, recv.mtype.as(MClassType))
                if mtype isa MNullableType then
                        v.write_attribute(self.mpropdef.mproperty, recv, v.null_instance)
                end
        end

        private fun evaluate_expr(v: NaiveInterpreter, recv: Instance): Instance
        do
                assert recv isa MutableInstance
                var f = new Frame(self, self.mpropdef.as(not null), [recv])
                v.frames.unshift(f)

                var val

                var nexpr = self.n_expr
                var nblock = self.n_block
                if nexpr != null then
                        val = v.expr(nexpr)
                else if nblock != null then
                        v.stmt(nblock)
                        assert v.returnmark == f
                        val = v.escapevalue
                        v.returnmark = null
                        v.escapevalue = null
                else
                        abort
                end
                assert val != null

                v.frames.shift
                assert not v.is_escaping
                v.write_attribute(self.mpropdef.mproperty, recv, val)
                return val
        end
end

redef class AClassdef
        # Execute an implicit `mpropdef` associated with the current node.
        private fun call(v: NaiveInterpreter, mpropdef: MMethodDef, args: Array[Instance]): nullable Instance
        do
                if mpropdef.mproperty.is_root_init then
                        assert args.length == 1
                        if not mpropdef.is_intro then
                                # standard call-next-method
                                var superpd = mpropdef.lookup_next_definition(v.mainmodule, args.first.mtype)
                                v.call(superpd, args)
                        end
                        return null
                else
                        abort
                end
        end
end

redef class AExpr
        # Evaluate the node as a possible expression.
        # Return a possible value
        # NOTE: Do not call this method directly, but use `v.expr`
        # This method is here to be implemented by subclasses.
        protected fun expr(v: NaiveInterpreter): nullable Instance
        do
                fatal(v, "NOT YET IMPLEMENTED expr {class_name}")
                abort
        end

        # Evaluate the node as a statement.
        # NOTE: Do not call this method directly, but use `v.stmt`
        # This method is here to be implemented by subclasses (no need to return something).
        protected fun stmt(v: NaiveInterpreter)
        do
                expr(v)
        end

end

redef class ABlockExpr
        redef fun expr(v)
        do
                var last = self.n_expr.last
                for e in self.n_expr do
                        if e == last then break
                        v.stmt(e)
                        if v.is_escaping then return null
                end
                return last.expr(v)
        end

        redef fun stmt(v)
        do
                for e in self.n_expr do
                        v.stmt(e)
                        if v.is_escaping then return
                end
        end
end

redef class AVardeclExpr
        redef fun stmt(v)
        do
                var ne = self.n_expr
                if ne != null then
                        var i = v.expr(ne)
                        if i == null then return
                        v.write_variable(self.variable.as(not null), i)
                end
        end
end

redef class AVarExpr
        redef fun expr(v)
        do
                return v.read_variable(self.variable.as(not null))
        end
end

redef class AVarAssignExpr
        redef fun expr(v)
        do
                var i = v.expr(self.n_value)
                if i == null then return null
                v.write_variable(self.variable.as(not null), i)
                return i
        end
end

redef class AVarReassignExpr
        redef fun stmt(v)
        do
                var variable = self.variable.as(not null)
                var vari = v.read_variable(variable)
                var value = v.expr(self.n_value)
                if value == null then return
                var res = v.callsite(reassign_callsite, [vari, value])
                assert res != null
                v.write_variable(variable, res)
        end
end

redef class ASelfExpr
        redef fun expr(v)
        do
                return v.frame.arguments.first
        end
end

redef class AEscapeExpr
        redef fun stmt(v)
        do
                var ne = self.n_expr
                if ne != null then
                        var i = v.expr(ne)
                        if i == null then return
                        v.escapevalue = i
                end
                v.escapemark = self.escapemark
        end
end

redef class AReturnExpr
        redef fun stmt(v)
        do
                var ne = self.n_expr
                if ne != null then
                        var i = v.expr(ne)
                        if i == null then return
                        v.escapevalue = i
                end
                v.returnmark = v.frame
        end
end

redef class AAbortExpr
        redef fun stmt(v)
        do
                fatal(v, "Aborted")
                exit(1)
        end
end

redef class AIfExpr
        redef fun expr(v)
        do
                var cond = v.expr(self.n_expr)
                if cond == null then return null
                if cond.is_true then
                        return v.expr(self.n_then.as(not null))
                else
                        return v.expr(self.n_else.as(not null))
                end
        end

        redef fun stmt(v)
        do
                var cond = v.expr(self.n_expr)
                if cond == null then return
                if cond.is_true then
                        v.stmt(self.n_then)
                else
                        v.stmt(self.n_else)
                end
        end
end

redef class AIfexprExpr
        redef fun expr(v)
        do
                var cond = v.expr(self.n_expr)
                if cond == null then return null
                if cond.is_true then
                        return v.expr(self.n_then)
                else
                        return v.expr(self.n_else)
                end
        end
end

redef class ADoExpr
        redef fun stmt(v)
        do
                v.stmt(self.n_block)
                v.is_escape(self.break_mark) # Clear the break (if any)
        end
end

redef class AWhileExpr
        redef fun stmt(v)
        do
                loop
                        var cond = v.expr(self.n_expr)
                        if cond == null then return
                        if not cond.is_true then return
                        v.stmt(self.n_block)
                        if v.is_escape(self.break_mark) then return
                        v.is_escape(self.continue_mark) # Clear the break
                        if v.is_escaping then return
                end
        end
end

redef class ALoopExpr
        redef fun stmt(v)
        do
                loop
                        v.stmt(self.n_block)
                        if v.is_escape(self.break_mark) then return
                        v.is_escape(self.continue_mark) # Clear the break
                        if v.is_escaping then return
                end
        end
end

redef class AForExpr
        redef fun stmt(v)
        do
                var col = v.expr(self.n_expr)
                if col == null then return
                if col.mtype isa MNullType then fatal(v, "Receiver is null")

                #self.debug("col {col}")
                var iter = v.callsite(method_iterator, [col]).as(not null)
                #self.debug("iter {iter}")
                loop
                        var isok = v.callsite(method_is_ok, [iter]).as(not null)
                        if not isok.is_true then break
                        if self.variables.length == 1 then
                                var item = v.callsite(method_item, [iter]).as(not null)
                                #self.debug("item {item}")
                                v.write_variable(self.variables.first, item)
                        else if self.variables.length == 2 then
                                var key = v.callsite(method_key, [iter]).as(not null)
                                v.write_variable(self.variables[0], key)
                                var item = v.callsite(method_item, [iter]).as(not null)
                                v.write_variable(self.variables[1], item)
                        else
                                abort
                        end
                        v.stmt(self.n_block)
                        if v.is_escape(self.break_mark) then break
                        v.is_escape(self.continue_mark) # Clear the break
                        if v.is_escaping then break
                        v.callsite(method_next, [iter])
                end
                var method_finish = self.method_finish
                if method_finish != null then
                        v.callsite(method_finish, [iter])
                end
        end
end

redef class AAssertExpr
        redef fun stmt(v)
        do
                var cond = v.expr(self.n_expr)
                if cond == null then return
                if not cond.is_true then
                        v.stmt(self.n_else)
                        if v.is_escaping then return
                        var nid = self.n_id
                        if nid != null then
                                fatal(v, "Assert '{nid.text}' failed")
                        else
                                fatal(v, "Assert failed")
                        end
                        exit(1)
                end
        end
end

redef class AOrExpr
        redef fun expr(v)
        do
                var cond = v.expr(self.n_expr)
                if cond == null then return null
                if cond.is_true then return cond
                return v.expr(self.n_expr2)
        end
end

redef class AImpliesExpr
        redef fun expr(v)
        do
                var cond = v.expr(self.n_expr)
                if cond == null then return null
                if not cond.is_true then return v.true_instance
                return v.expr(self.n_expr2)
        end
end

redef class AAndExpr
        redef fun expr(v)
        do
                var cond = v.expr(self.n_expr)
                if cond == null then return null
                if not cond.is_true then return cond
                return v.expr(self.n_expr2)
        end
end

redef class ANotExpr
        redef fun expr(v)
        do
                var cond = v.expr(self.n_expr)
                if cond == null then return null
                return v.bool_instance(not cond.is_true)
        end
end

redef class AOrElseExpr
        redef fun expr(v)
        do
                var i = v.expr(self.n_expr)
                if i == null then return null
                if i != v.null_instance then return i
                return v.expr(self.n_expr2)
        end
end

redef class AIntExpr
        redef fun expr(v)
        do
                return v.int_instance(self.value.as(not null))
        end
end

redef class AFloatExpr
        redef fun expr(v)
        do
                return v.float_instance(self.value.as(not null))
        end
end

redef class ACharExpr
        redef fun expr(v)
        do
                return v.char_instance(self.value.as(not null))
        end
end

redef class AArrayExpr
        redef fun expr(v)
        do
                var val = new Array[Instance]
                var old_comprehension = v.frame.comprehension
                v.frame.comprehension = val
                for nexpr in self.n_exprs do
                        if nexpr isa AForExpr then
                                v.stmt(nexpr)
                        else
                                var i = v.expr(nexpr)
                                if i == null then return null
                                val.add(i)
                        end
                end
                v.frame.comprehension = old_comprehension
                var mtype = v.unanchor_type(self.mtype.as(not null)).as(MClassType)
                var elttype = mtype.arguments.first
                return v.array_instance(val, elttype)
        end
end

redef class AStringFormExpr
        redef fun expr(v)
        do
                var txt = self.value.as(not null)
                return v.string_instance(txt)
        end
end

redef class ASuperstringExpr
        redef fun expr(v)
        do
                var array = new Array[Instance]
                for nexpr in n_exprs do
                        var i = v.expr(nexpr)
                        if i == null then return null
                        array.add(i)
                end
                var i = v.array_instance(array, v.get_primitive_class("Object").mclass_type)
                var res = v.send(v.force_get_primitive_method("to_s", i.mtype), [i])
                assert res != null
                return res
        end
end

redef class ACrangeExpr
        redef fun expr(v)
        do
                var e1 = v.expr(self.n_expr)
                if e1 == null then return null
                var e2 = v.expr(self.n_expr2)
                if e2 == null then return null
                var mtype = v.unanchor_type(self.mtype.as(not null))
                var res = new MutableInstance(mtype)
                v.init_instance(res)
                v.callsite(init_callsite, [res, e1, e2])
                return res
        end
end

redef class AOrangeExpr
        redef fun expr(v)
        do
                var e1 = v.expr(self.n_expr)
                if e1 == null then return null
                var e2 = v.expr(self.n_expr2)
                if e2 == null then return null
                var mtype = v.unanchor_type(self.mtype.as(not null))
                var res = new MutableInstance(mtype)
                v.init_instance(res)
                v.callsite(init_callsite, [res, e1, e2])
                return res
        end
end

redef class ATrueExpr
        redef fun expr(v)
        do
                return v.bool_instance(true)
        end
end

redef class AFalseExpr
        redef fun expr(v)
        do
                return v.bool_instance(false)
        end
end

redef class ANullExpr
        redef fun expr(v)
        do
                return v.null_instance
        end
end

redef class AIsaExpr
        redef fun expr(v)
        do
                var i = v.expr(self.n_expr)
                if i == null then return null
                var mtype = v.unanchor_type(self.cast_type.as(not null))
                return v.bool_instance(v.is_subtype(i.mtype, mtype))
        end
end

redef class AAsCastExpr
        redef fun expr(v)
        do
                var i = v.expr(self.n_expr)
                if i == null then return null
                var mtype = self.mtype.as(not null)
                var amtype = v.unanchor_type(mtype)
                if not v.is_subtype(i.mtype, amtype) then
                        fatal(v, "Cast failed. Expected `{amtype}`, got `{i.mtype}`")
                end
                return i
        end
end

redef class AAsNotnullExpr
        redef fun expr(v)
        do
                var i = v.expr(self.n_expr)
                if i == null then return null
                if i.mtype isa MNullType then
                        fatal(v, "Cast failed")
                end
                return i
        end
end

redef class AParExpr
        redef fun expr(v)
        do
                return v.expr(self.n_expr)
        end
end

redef class AOnceExpr
        redef fun expr(v)
        do
                if v.onces.has_key(self) then
                        return v.onces[self]
                else
                        var res = v.expr(self.n_expr)
                        if res == null then return null
                        v.onces[self] = res
                        return res
                end
        end
end

redef class ASendExpr
        redef fun expr(v)
        do
                var recv = v.expr(self.n_expr)
                if recv == null then return null
                var args = v.varargize(callsite.mpropdef, recv, self.raw_arguments)
                if args == null then return null

                var res = v.callsite(callsite, args)
                return res
        end
end

redef class ASendReassignFormExpr
        redef fun stmt(v)
        do
                var recv = v.expr(self.n_expr)
                if recv == null then return
                var args = v.varargize(callsite.mpropdef, recv, self.raw_arguments)
                if args == null then return
                var value = v.expr(self.n_value)
                if value == null then return

                var read = v.callsite(callsite, args)
                assert read != null

                var write = v.callsite(reassign_callsite, [read, value])
                assert write != null

                args.add(write)

                v.callsite(write_callsite, args)
        end
end

redef class ASuperExpr
        redef fun expr(v)
        do
                var recv = v.frame.arguments.first

                var callsite = self.callsite
                if callsite != null then
                        var args = v.varargize(callsite.mpropdef, recv, self.n_args.n_exprs)
                        if args == null then return null
                        # Add additional arguments for the super init call
                        if args.length == 1 then
                                for i in [0..callsite.msignature.arity[ do
                                        args.add(v.frame.arguments[i+1])
                                end
                        end
                        # Super init call
                        var res = v.callsite(callsite, args)
                        return res
                end

                # standard call-next-method
                var mpropdef = self.mpropdef
                mpropdef = mpropdef.lookup_next_definition(v.mainmodule, recv.mtype)

                var args = v.varargize(mpropdef, recv, self.n_args.n_exprs)
                if args == null then return null

                if args.length == 1 then
                        args = v.frame.arguments
                end
                var res = v.call(mpropdef, args)
                return res
        end
end

redef class ANewExpr
        redef fun expr(v)
        do
                var mtype = v.unanchor_type(self.recvtype.as(not null))
                var recv: Instance = new MutableInstance(mtype)
                v.init_instance(recv)
                var args = v.varargize(callsite.mpropdef, recv, self.n_args.n_exprs)
                if args == null then return null
                var res2 = v.callsite(callsite, args)
                if res2 != null then
                        #self.debug("got {res2} from {mproperty}. drop {recv}")
                        return res2
                end
                return recv
        end
end

redef class AAttrExpr
        redef fun expr(v)
        do
                var recv = v.expr(self.n_expr)
                if recv == null then return null
                if recv.mtype isa MNullType then fatal(v, "Receiver is null")
                var mproperty = self.mproperty.as(not null)
                return v.read_attribute(mproperty, recv)
        end
end

redef class AAttrAssignExpr
        redef fun stmt(v)
        do
                var recv = v.expr(self.n_expr)
                if recv == null then return
                if recv.mtype isa MNullType then fatal(v, "Receiver is null")
                var i = v.expr(self.n_value)
                if i == null then return
                var mproperty = self.mproperty.as(not null)
                v.write_attribute(mproperty, recv, i)
        end
end

redef class AAttrReassignExpr
        redef fun stmt(v)
        do
                var recv = v.expr(self.n_expr)
                if recv == null then return
                if recv.mtype isa MNullType then fatal(v, "Receiver is null")
                var value = v.expr(self.n_value)
                if value == null then return
                var mproperty = self.mproperty.as(not null)
                var attr = v.read_attribute(mproperty, recv)
                var res = v.callsite(reassign_callsite, [attr, value])
                assert res != null
                v.write_attribute(mproperty, recv, res)
        end
end

redef class AIssetAttrExpr
        redef fun expr(v)
        do
                var recv = v.expr(self.n_expr)
                if recv == null then return null
                if recv.mtype isa MNullType then fatal(v, "Receiver is null")
                var mproperty = self.mproperty.as(not null)
                return v.bool_instance(v.isset_attribute(mproperty, recv))
        end
end

redef class ADebugTypeExpr
        redef fun stmt(v)
        do
                # do nothing
        end
end