Rename REAMDE to README.md

[nit.git] / src / transform.nit

# This file is part of NIT ( http://www.nitlanguage.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.

# Thansformations that simplify the AST of expressions
# This module transform complex AST `AExpr` nodes into simplier ones
module transform

import astbuilder
import astvalidation
import semantize
intrude import semantize::scope
intrude import semantize::typing

redef class ToolContext
        var transform_phase: Phase = new TransformPhase(self, [typing_phase, auto_super_init_phase])

        # --no-shortcut-range
        var opt_no_shortcut_range: OptionBool = new OptionBool("Always instantiate a range and its iterator on 'for' loops", "--no-shortcut-range")

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

private class TransformPhase
        super Phase

        redef fun process_npropdef(npropdef: APropdef)
        do
                var val

                var m = npropdef.mpropdef
                if m == null then return
                var v = new TransformVisitor(self, m)
                v.enter_visit(npropdef)

                val = new ASTValidationVisitor
                val.enter_visit(npropdef)
        end
end

private class TransformVisitor
        super Visitor

        var phase: TransformPhase
        var mmodule: MModule is noinit
        var mclassdef: MClassDef is noinit
        var mpropdef: MPropDef
        var builder: ASTBuilder is noinit

        init
        do
                self.mclassdef = mpropdef.mclassdef
                self.mmodule = mclassdef.mmodule
                self.builder = new ASTBuilder(mmodule, mpropdef.mclassdef.bound_mtype)
        end

        redef fun visit(node)
        do
                if node isa AAnnotations then return
                node.full_transform_visitor(self)
        end

        # Get a primitive method or display a fatal error on `location`.
        fun get_method(location: AExpr, name: String, recv: MClass): MMethod
        do
                return phase.toolcontext.modelbuilder.force_get_primitive_method(location, name, recv, mmodule)
        end
end

redef class ANode
        private fun full_transform_visitor(v: TransformVisitor)
        do
                visit_all(v)
                accept_transform_visitor(v)
        end
        private fun accept_transform_visitor(v: TransformVisitor)
        do
        end
end

redef class AExpr
        redef fun full_transform_visitor(v: TransformVisitor)
        do
                var na = comprehension
                if na != null then
                        # We are building a comprehension array `array`
                        # Replace `self` with `array.push(self)`
                        var place = detach_with_placeholder
                        var recv = na.nnew.make_var_read
                        var nadd = v.builder.make_call(recv, na.push_callsite.as(not null), [self])
                        place.replace_with(nadd)
                end
                super
        end

        redef fun replace_with(other)
        do
                super
                if other isa AExpr then
                        if other.implicit_cast_to == null then other.implicit_cast_to = implicit_cast_to
                end
        end
end

redef class AVardeclExpr
        # `var x = y` is replaced with `x = y`
        #
        # Declarations are only useful for scope rules
        # Once names are associated with real objects, ther declaration become useless
        # Therefore, if there is no initial value, then just ignore it
        # Else, replace it with a simple assignment
        redef fun accept_transform_visitor(v)
        do
                var nexpr = n_expr
                if nexpr == null then
                        # do nothing
                        # note: not detached because the collection is currently under iteration
                else
                        var nvar = v.builder.make_var_assign(self.variable.as(not null), nexpr)
                        replace_with(nvar)
                end
        end
end

redef class AIfexprExpr
        # is replaced with `AIfExpr`
        # Expression if and statement-if use two distinct classes for historical reasons
        # However, on can replace the `AIfexprExpr` with the simpler `AIfExpr`
        redef fun accept_transform_visitor(v)
        do
                var nif = v.builder.make_if(n_expr, self.mtype)
                nif.n_then.add(n_then)
                nif.n_else.add(n_else)

                replace_with(nif)
        end
end

redef class AOrExpr
        # `x or y` is replaced with `if x then x else y`
        redef fun accept_transform_visitor(v)
        do
                var nif = v.builder.make_if(n_expr, self.mtype)
                nif.n_then.add(n_expr.make_var_read)
                nif.n_else.add(n_expr2)

                replace_with(nif)
        end
end

redef class AImpliesExpr
        redef fun accept_transform_visitor(v)
        do
                # TODO
        end
end

redef class AAndExpr
        # `x and y` is replaced with `if x then y else x`
        redef fun accept_transform_visitor(v)
        do
                var nif = v.builder.make_if(n_expr, self.mtype)
                nif.n_then.add(n_expr2)
                nif.n_else.add(n_expr.make_var_read)

                replace_with(nif)
        end
end

redef class AWhileExpr
        redef fun accept_transform_visitor(v)
        do
                var nloop = v.builder.make_loop
                var nif = v.builder.make_if(n_expr, null)
                nloop.add nif

                var nblock = n_block
                if nblock != null then nif.n_then.add nblock

                var escapemark = self.break_mark.as(not null)
                var nbreak = v.builder.make_break(escapemark)
                nif.n_else.add nbreak

                nloop.break_mark = self.break_mark
                nloop.continue_mark = self.continue_mark

                replace_with(nloop)
        end
end

redef class AForExpr
        redef fun accept_transform_visitor(v)
        do
                var escapemark = self.break_mark
                assert escapemark != null

                var nblock = v.builder.make_block

                var nexpr = n_expr

                # Shortcut on explicit range
                # Avoid the instantiation of the range and the iterator
                if self.variables.length == 1 and nexpr isa ARangeExpr and not v.phase.toolcontext.opt_no_shortcut_range.value then
                        var variable = variables.first
                        nblock.add v.builder.make_var_assign(variable, nexpr.n_expr)
                        var to = nexpr.n_expr2
                        nblock.add to

                        var nloop = v.builder.make_loop
                        nloop.break_mark = escapemark
                        nblock.add nloop

                        var is_ok = v.builder.make_call(v.builder.make_var_read(variable, variable.declared_type.as(not null)), method_lt.as(not null), [to.make_var_read])

                        var nif = v.builder.make_if(is_ok, null)
                        nloop.add nif

                        var nthen = nif.n_then
                        var ndo = v.builder.make_do
                        ndo.break_mark = escapemark.continue_mark
                        nthen.add ndo

                        ndo.add self.n_block.as(not null)

                        var one = v.builder.make_int(1)
                        var succ = v.builder.make_call(v.builder.make_var_read(variable, variable.declared_type.as(not null)), method_successor.as(not null), [one])
                        nthen.add v.builder.make_var_assign(variable, succ)

                        var nbreak = v.builder.make_break(escapemark)
                        nif.n_else.add nbreak

                        replace_with(nblock)
                        return
                end

                nblock.add nexpr

                var iter = v.builder.make_call(nexpr.make_var_read, method_iterator.as(not null), null)
                nblock.add iter

                var nloop = v.builder.make_loop
                nloop.break_mark = escapemark
                nblock.add nloop

                var is_ok = v.builder.make_call(iter.make_var_read, method_is_ok.as(not null), null)

                var nif = v.builder.make_if(is_ok, null)
                nloop.add nif

                var nthen = nif.n_then
                var ndo = v.builder.make_do
                ndo.break_mark = escapemark.continue_mark
                nthen.add ndo

                if self.variables.length == 1 then
                        var item = v.builder.make_call(iter.make_var_read, method_item.as(not null), null)
                        ndo.add v.builder.make_var_assign(variables.first, item)
                else if self.variables.length == 2 then
                        var key = v.builder.make_call(iter.make_var_read, method_key.as(not null), null)
                        ndo.add v.builder.make_var_assign(variables[0], key)
                        var item = v.builder.make_call(iter.make_var_read, method_item.as(not null), null)
                        ndo.add v.builder.make_var_assign(variables[1], item)
                else
                        abort
                end

                ndo.add self.n_block.as(not null)

                nthen.add v.builder.make_call(iter.make_var_read, method_next.as(not null), null)

                var nbreak = v.builder.make_break(escapemark)
                nif.n_else.add nbreak

                var method_finish = self.method_finish
                if method_finish != null then
                        nblock.add v.builder.make_call(iter.make_var_read, method_finish, null)
                end

                replace_with(nblock)
        end
end

redef class AWithExpr
        # is replaced with a do/end and injected calls to `start` and `finish`
        #
        # Basically, the following
        #
        # ~~~nitish
        # with expr do
        #   block
        # end label l
        # ~~~
        #
        # is transformed into
        #
        # ~~~nitish
        # var x = expr
        # do
        #   x.start
        #   block
        # end label l
        # x.finish
        # ~~~
        #
        # The point is that `finish` is called even if the block is escaped.
        redef fun accept_transform_visitor(v)
        do
                var escapemark = self.break_mark
                assert escapemark != null

                var nblock = v.builder.make_block

                var nexpr = n_expr

                nblock.add nexpr

                var ndo = v.builder.make_do
                ndo.break_mark = escapemark

                var start = v.builder.make_call(nexpr.make_var_read, method_start.as(not null), null)

                ndo.add start

                ndo.add self.n_block.as(not null)

                nblock.add ndo

                nblock.add v.builder.make_call(nexpr.make_var_read, method_finish.as(not null), null)

                replace_with(nblock)
        end
end

redef class AArrayExpr
        # `[x,y]` is replaced with
        #
        # ~~~nitish
        # var t = new Array[X].with_capacity(2)
        # t.add(x)
        # t.add(y)
        # t
        # ~~~
        redef fun full_transform_visitor(v)
        do
                var nblock = v.builder.make_block

                var nnew = v.builder.make_new(with_capacity_callsite.as(not null), [v.builder.make_int(n_exprs.length)])
                self.nnew = nnew

                nblock.add nnew

                super

                for nexpr in self.n_exprs do
                        nblock.add nexpr
                end
                var nres = nnew.make_var_read
                nblock.add nres

                replace_with(nblock)
        end

        private var nnew: ANewExpr is noinit
end

redef class ACrangeExpr
        # `[x..y]` is replaced with `new Range[X](x,y)`
        redef fun accept_transform_visitor(v)
        do
                if parent isa AForExpr then return # to permit shortcut ranges
                replace_with(v.builder.make_new(init_callsite.as(not null), [n_expr, n_expr2]))
        end
end

redef class AOrangeExpr
        # `[x..y[` is replaced with `new Range[X].without_last(x,y)`
        redef fun accept_transform_visitor(v)
        do
                if parent isa AForExpr then return # to permit shortcut ranges
                replace_with(v.builder.make_new(init_callsite.as(not null), [n_expr, n_expr2]))
        end
end

redef class AParExpr
        # `(x)` is replaced with `x`
        redef fun accept_transform_visitor(v)
        do
                replace_with(n_expr)
        end
end

redef class ASendReassignFormExpr
        # `x.foo(y)+=z` is replaced with
        #
        # ~~~nitish
        # x.foo(y) = x.foo(y) + z
        # ~~~
        #
        # witch is, in reality:
        #
        # ~~~nitish
        # x."foo="(y, x.foo(y)."+"(z))
        # ~~~
        redef fun accept_transform_visitor(v)
        do
                var nblock = v.builder.make_block
                nblock.add(n_expr)

                var read_args = new Array[AExpr]
                var write_args = new Array[AExpr]
                for a in raw_arguments do
                        nblock.add(a)
                        read_args.add(a.make_var_read)
                        write_args.add(a.make_var_read)
                end

                var nread = v.builder.make_call(n_expr.make_var_read, callsite.as(not null), read_args)

                var nnewvalue = v.builder.make_call(nread, reassign_callsite.as(not null), [n_value])

                write_args.add(nnewvalue)
                var nwrite = v.builder.make_call(n_expr.make_var_read, write_callsite.as(not null), write_args)
                nblock.add(nwrite)

                replace_with(nblock)
        end
end

redef class AVarReassignExpr
        # `v += z` is replaced with `v = v + z`
        redef fun accept_transform_visitor(v)
        do
                var variable = self.variable.as(not null)

                var nread = v.builder.make_var_read(variable, read_type.as(not null))

                var nnewvalue = v.builder.make_call(nread, reassign_callsite.as(not null), [n_value])
                var nwrite = v.builder.make_var_assign(variable, nnewvalue)

                replace_with(nwrite)
        end
end

redef class AAttrReassignExpr
        # `x.a += z` is replaced with `x.a = x.a + z`
        redef fun accept_transform_visitor(v)
        do
                var nblock = v.builder.make_block
                nblock.add(n_expr)
                var attribute = self.mproperty.as(not null)

                var nread = v.builder.make_attr_read(n_expr.make_var_read, attribute)
                var nnewvalue = v.builder.make_call(nread, reassign_callsite.as(not null), [n_value])
                var nwrite = v.builder.make_attr_assign(n_expr.make_var_read, attribute, nnewvalue)
                nblock.add(nwrite)

                replace_with(nblock)
        end
end