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. :^)

1 files changed, 59 insertions, 0 deletions

diff --git a/Libraries/LibJS/Interpreter.h b/Libraries/LibJS/Interpreter.h
new file mode 100644
index 0000000000..cdc4bda5a7
--- /dev/null
+++ b/Libraries/LibJS/Interpreter.h
@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Vector.h>
+#include <LibJS/Forward.h>
+
+namespace JS {
+
+struct ScopeFrame {
+    const ScopeNode& scope_node;
+};
+
+class Interpreter {
+public:
+    Interpreter();
+    ~Interpreter();
+
+    Value run(const ScopeNode&);
+
+    Object& global_object() { return *m_global_object; }
+    const Object& global_object() const { return *m_global_object; }
+
+    void do_return();
+
+private:
+    void enter_scope(const ScopeNode&);
+    void exit_scope(const ScopeNode&);
+
+    Vector<ScopeFrame> m_scope_stack;
+
+    Object* m_global_object { nullptr };
+};
+
+}