LibJS: Add basic support for (scoped) variables

It's now possible to assign expressions to variables. The variables are
put into the current scope of the interpreter.

Variable lookup follows the scope chain, ending in the global object.

1 files changed, 60 insertions, 0 deletions

diff --git a/Libraries/LibJS/AST.cpp b/Libraries/LibJS/AST.cpp
index 2e6acb947c..acac0b3273 100644
--- a/Libraries/LibJS/AST.cpp
+++ b/Libraries/LibJS/AST.cpp
@@ -393,4 +393,64 @@ void WhileStatement::dump(int indent) const
     body().dump(indent + 1);
 }
 
+Value Identifier::execute(Interpreter& interpreter) const
+{
+    return interpreter.get_variable(string());
+}
+
+void Identifier::dump(int indent) const
+{
+    print_indent(indent);
+    printf("Identifier \"%s\"\n", m_string.characters());
+}
+
+Value AssignmentExpression::execute(Interpreter& interpreter) const
+{
+    ASSERT(m_lhs->is_identifier());
+    auto name = static_cast<const Identifier&>(*m_lhs).string();
+    auto rhs_result = m_rhs->execute(interpreter);
+
+    switch (m_op) {
+    case AssignmentOp::Assign:
+        interpreter.set_variable(name, rhs_result);
+        break;
+    }
+    return rhs_result;
+}
+
+void AssignmentExpression::dump(int indent) const
+{
+    const char* op_string = nullptr;
+    switch (m_op) {
+    case AssignmentOp::Assign:
+        op_string = "=";
+        break;
+    }
+
+    ASTNode::dump(indent);
+    print_indent(indent + 1);
+    printf("%s\n", op_string);
+    m_lhs->dump(indent + 1);
+    m_rhs->dump(indent + 1);
+}
+
+Value VariableDeclaration::execute(Interpreter& interpreter) const
+{
+    interpreter.declare_variable(name().string());
+    if (m_initializer) {
+        auto initalizer_result = m_initializer->execute(interpreter);
+        interpreter.set_variable(name().string(), initalizer_result);
+    }
+    return js_undefined();
+}
+
+
+void VariableDeclaration::dump(int indent) const
+{
+    ASTNode::dump(indent);
+    m_name->dump(indent + 1);
+    if (m_initializer)
+        m_initializer->dump(indent + 1);
+}
+
 }