ed80952cb6
This patch replaces the old variable lookup logic with a new one based
on lexical environments.
This brings us closer to the way JavaScript is actually specced, and
also gives us some basic support for closures.
The interpreter's call stack frames now have a pointer to the lexical
environment for that frame. Each lexical environment can have a chain
of parent environments.
Before calling a Function, we first ask it to create_environment().
This gives us a new LexicalEnvironment for that function, which has the
function's lexical parent's environment as its parent. This allows
inner functions to access variables in their outer function:
function foo() { <-- LexicalEnvironment A
var x = 1;
function() { <-- LexicalEnvironment B (parent: A)
console.log(x);
}
}
If we return the result of a function expression from a function, that
new function object will keep a reference to its parent environment,
which is how we get closures. :^)
I'm pretty sure I didn't get everything right here, but it's a pretty
good start. This is quite a bit slower than before, but also correcter!
64 lines
2.3 KiB
C++
64 lines
2.3 KiB
C++
/*
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* Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#pragma once
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#include <AK/FlyString.h>
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#include <AK/HashMap.h>
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#include <LibJS/Runtime/Cell.h>
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#include <LibJS/Runtime/Value.h>
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namespace JS {
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struct Variable {
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Value value;
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DeclarationKind declaration_kind;
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};
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class LexicalEnvironment final : public Cell {
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public:
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LexicalEnvironment();
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LexicalEnvironment(HashMap<FlyString, Variable> variables, LexicalEnvironment* parent);
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virtual ~LexicalEnvironment() override;
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LexicalEnvironment* parent() { return m_parent; }
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Optional<Variable> get(const FlyString&) const;
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void set(const FlyString&, Variable);
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void clear();
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const HashMap<FlyString, Variable>& variables() const { return m_variables; }
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private:
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virtual const char* class_name() const override { return "LexicalEnvironment"; }
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virtual void visit_children(Visitor&) override;
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LexicalEnvironment* m_parent { nullptr };
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HashMap<FlyString, Variable> m_variables;
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};
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}
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