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LibJS: Start building a JavaScript engine for SerenityOS :^)
I always tell people to start building things by working on the thing that seems the most interesting right now. The most interesting thing here was an AST + simple interpreter, so that's where we start! There is no lexer or parser yet, we build an AST directly and then execute it in the interpreter, producing a return value. This seems like the start of something interesting. :^)
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Libraries/LibJS/AST.cpp
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144
Libraries/LibJS/AST.cpp
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/*
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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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#include <LibJS/AST.h>
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#include <LibJS/Function.h>
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#include <LibJS/Interpreter.h>
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#include <LibJS/Value.h>
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#include <stdio.h>
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namespace JS {
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Value ScopeNode::execute(Interpreter& interpreter) const
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{
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return interpreter.run(*this);
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}
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Value FunctionDeclaration::execute(Interpreter& interpreter) const
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{
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auto* function = new Function(name(), body());
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interpreter.global_object().put(m_name, Value(function));
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return Value(function);
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}
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Value CallExpression::execute(Interpreter& interpreter) const
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{
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auto callee = interpreter.global_object().get(name());
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ASSERT(callee.is_object());
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auto* callee_object = callee.as_object();
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ASSERT(callee_object->is_function());
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auto& function = static_cast<Function&>(*callee_object);
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return interpreter.run(function.body());
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}
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Value ReturnStatement::execute(Interpreter& interpreter) const
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{
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auto value = argument().execute(interpreter);
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interpreter.do_return();
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return value;
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}
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Value add(Value lhs, Value rhs)
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{
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ASSERT(lhs.is_number());
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ASSERT(rhs.is_number());
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return Value(lhs.as_double() + rhs.as_double());
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}
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Value sub(Value lhs, Value rhs)
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{
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ASSERT(lhs.is_number());
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ASSERT(rhs.is_number());
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return Value(lhs.as_double() - rhs.as_double());
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}
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Value BinaryExpression::execute(Interpreter& interpreter) const
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{
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auto lhs_result = m_lhs->execute(interpreter);
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auto rhs_result = m_rhs->execute(interpreter);
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switch (m_op) {
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case BinaryOp::Plus:
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return add(lhs_result, rhs_result);
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case BinaryOp::Minus:
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return sub(lhs_result, rhs_result);
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}
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ASSERT_NOT_REACHED();
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}
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static void print_indent(int indent)
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{
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for (int i = 0; i < indent * 2; ++i)
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putchar(' ');
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}
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void ASTNode::dump(int indent) const
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{
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print_indent(indent);
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printf("%s\n", class_name());
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}
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void ScopeNode::dump(int indent) const
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{
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ASTNode::dump(indent);
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for (auto& child : children())
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child.dump(indent + 1);
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}
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void BinaryExpression::dump(int indent) const
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{
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ASTNode::dump(indent);
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m_lhs->dump(indent + 1);
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m_rhs->dump(indent + 1);
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}
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void CallExpression::dump(int indent) const
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{
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print_indent(indent);
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printf("%s '%s'\n", class_name(), name().characters());
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}
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void Literal::dump(int indent) const
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{
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print_indent(indent);
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printf("%d\n", (i32)m_value.as_double());
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}
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void FunctionDeclaration::dump(int indent) const
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{
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print_indent(indent);
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printf("%s '%s'\n", class_name(), name().characters());
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body().dump(indent + 1);
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}
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void ReturnStatement::dump(int indent) const
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{
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ASTNode::dump(indent);
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argument().dump(indent + 1);
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}
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}
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