LibJS: Add NativeFunction, a callable wrapper around a C++ lambda

This can be used to implement arbitrary functionality, callable from
JavaScript.

To make this work, I had to change the way CallExpression passes
arguments to the callee. Instead of a HashMap<String, Value>, we now
pass an ordered list of Argument { String name; Value value; }.

This patch includes a native "print(argument)" function. :^)

8 files changed, 129 insertions, 18 deletions

diff --git a/Libraries/LibJS/AST.cpp b/Libraries/LibJS/AST.cpp
index 7539dcf0f3..bc65f30c11 100644
--- a/Libraries/LibJS/AST.cpp
+++ b/Libraries/LibJS/AST.cpp
@@ -29,6 +29,7 @@
 #include <LibJS/AST.h>
 #include <LibJS/Function.h>
 #include <LibJS/Interpreter.h>
+#include <LibJS/NativeFunction.h>
 #include <LibJS/PrimitiveString.h>
 #include <LibJS/Value.h>
 #include <stdio.h>
@@ -62,20 +63,25 @@ Value CallExpression::execute(Interpreter& interpreter) const
     auto callee = interpreter.get_variable(name());
     ASSERT(callee.is_object());
     auto* callee_object = callee.as_object();
-    ASSERT(callee_object->is_function());
-    auto& function = static_cast<Function&>(*callee_object);
-
-    const size_t arguments_size = m_arguments.size();
-    ASSERT(function.parameters().size() == arguments_size);
-    HashMap<String, Value> passed_parameters;
-    for (size_t i = 0; i < arguments_size; ++i) {
-        auto name = function.parameters()[i];
+
+    Vector<Argument> passed_arguments;
+    for (size_t i = 0; i < m_arguments.size(); ++i) {
+        String name;
+        if (callee_object->is_function())
+            name = static_cast<Function&>(*callee_object).parameters()[i];
         auto value = m_arguments[i].execute(interpreter);
         dbg() << name << ": " << value;
-        passed_parameters.set(move(name), move(value));
+        passed_arguments.append({ move(name), move(value) });
     }
 
-    return interpreter.run(function.body(), move(passed_parameters), ScopeType::Function);
+    if (callee_object->is_function())
+        return interpreter.run(static_cast<Function&>(*callee_object).body(), move(passed_arguments), ScopeType::Function);
+
+    if (callee_object->is_native_function()) {
+        return static_cast<NativeFunction&>(*callee_object).native_function()(move(passed_arguments));
+    }
+
+    ASSERT_NOT_REACHED();
 }
 
 Value ReturnStatement::execute(Interpreter& interpreter) const
diff --git a/Libraries/LibJS/Forward.h b/Libraries/LibJS/Forward.h
index 4f38acf973..bb4f0499ba 100644
--- a/Libraries/LibJS/Forward.h
+++ b/Libraries/LibJS/Forward.h
@@ -29,6 +29,7 @@
 namespace JS {
 
 class ASTNode;
+class Argument;
 class Cell;
 class Expression;
 class Heap;
diff --git a/Libraries/LibJS/Interpreter.cpp b/Libraries/LibJS/Interpreter.cpp
index 8a569e0fe3..b62c7db5ca 100644
--- a/Libraries/LibJS/Interpreter.cpp
+++ b/Libraries/LibJS/Interpreter.cpp
@@ -27,8 +27,10 @@
 #include <AK/Badge.h>
 #include <LibJS/AST.h>
 #include <LibJS/Interpreter.h>
+#include <LibJS/NativeFunction.h>
 #include <LibJS/Object.h>
 #include <LibJS/Value.h>
+#include <stdio.h>
 
 namespace JS {
 
@@ -36,15 +38,20 @@ Interpreter::Interpreter()
     : m_heap(*this)
 {
     m_global_object = heap().allocate<Object>();
+    m_global_object->put("print", Value(heap().allocate<NativeFunction>([](Vector<Argument> arguments) -> Value {
+        for (auto& argument : arguments)
+            printf("%s ", argument.value.to_string().characters());
+        return js_undefined();
+    })));
 }
 
 Interpreter::~Interpreter()
 {
 }
 
-Value Interpreter::run(const ScopeNode& scope_node, HashMap<String, Value> scope_variables, ScopeType scope_type)
+Value Interpreter::run(const ScopeNode& scope_node, Vector<Argument> arguments, ScopeType scope_type)
 {
-    enter_scope(scope_node, move(scope_variables), scope_type);
+    enter_scope(scope_node, move(arguments), scope_type);
 
     Value last_value = js_undefined();
     for (auto& node : scope_node.children()) {
@@ -55,13 +62,12 @@ Value Interpreter::run(const ScopeNode& scope_node, HashMap<String, Value> scope
     return last_value;
 }
 
-void Interpreter::enter_scope(const ScopeNode& scope_node, HashMap<String, Value> scope_variables, ScopeType scope_type)
+void Interpreter::enter_scope(const ScopeNode& scope_node, Vector<Argument> arguments, ScopeType scope_type)
 {
     HashMap<String, Variable> scope_variables_with_declaration_type;
-    for (String name : scope_variables.keys()) {
-        scope_variables_with_declaration_type.set(name, { scope_variables.get(name).value(), DeclarationType::Var });
+    for (auto& argument : arguments) {
+        scope_variables_with_declaration_type.set(argument.name, { argument.value, DeclarationType::Var });
     }
-
     m_scope_stack.append({ scope_type, scope_node, move(scope_variables_with_declaration_type) });
 }
 
diff --git a/Libraries/LibJS/Interpreter.h b/Libraries/LibJS/Interpreter.h
index 39fd4166af..9164e286b3 100644
--- a/Libraries/LibJS/Interpreter.h
+++ b/Libraries/LibJS/Interpreter.h
@@ -27,6 +27,7 @@
 #pragma once
 
 #include <AK/HashMap.h>
+#include <AK/String.h>
 #include <AK/Vector.h>
 #include <LibJS/Forward.h>
 #include <LibJS/Heap.h>
@@ -50,12 +51,17 @@ struct ScopeFrame {
     HashMap<String, Variable> variables;
 };
 
+struct Argument {
+    String name;
+    Value value;
+};
+
 class Interpreter {
 public:
     Interpreter();
     ~Interpreter();
 
-    Value run(const ScopeNode&, HashMap<String, Value> scope_variables = {}, ScopeType = ScopeType::Block);
+    Value run(const ScopeNode&, Vector<Argument> = {}, ScopeType = ScopeType::Block);
 
     Object& global_object() { return *m_global_object; }
     const Object& global_object() const { return *m_global_object; }
@@ -71,7 +77,7 @@ public:
     void collect_roots(Badge<Heap>, HashTable<Cell*>&);
 
 private:
-    void enter_scope(const ScopeNode&, HashMap<String, Value> scope_variables, ScopeType);
+    void enter_scope(const ScopeNode&, Vector<Argument>, ScopeType);
     void exit_scope(const ScopeNode&);
 
     Heap m_heap;
diff --git a/Libraries/LibJS/Makefile b/Libraries/LibJS/Makefile
index 8e07c0c206..64d4b9bed2 100644
--- a/Libraries/LibJS/Makefile
+++ b/Libraries/LibJS/Makefile
@@ -6,6 +6,7 @@ OBJS = \
     HeapBlock.o \
     Interpreter.o \
     Lexer.o \
+    NativeFunction.o \
     Object.o \
     Parser.o \
     PrimitiveString.o \
diff --git a/Libraries/LibJS/NativeFunction.cpp b/Libraries/LibJS/NativeFunction.cpp
new file mode 100644
index 0000000000..92ad88b544
--- /dev/null
+++ b/Libraries/LibJS/NativeFunction.cpp
@@ -0,0 +1,42 @@
+/*
+ * 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.
+ */
+
+#include <LibJS/Interpreter.h>
+#include <LibJS/NativeFunction.h>
+#include <LibJS/Value.h>
+
+namespace JS {
+
+NativeFunction::NativeFunction(AK::Function<Value(Vector<Argument>)> native_function)
+    : m_native_function(move(native_function))
+{
+}
+
+NativeFunction::~NativeFunction()
+{
+}
+
+}
diff --git a/Libraries/LibJS/NativeFunction.h b/Libraries/LibJS/NativeFunction.h
new file mode 100644
index 0000000000..6d68148461
--- /dev/null
+++ b/Libraries/LibJS/NativeFunction.h
@@ -0,0 +1,48 @@
+/*
+ * 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/Function.h>
+#include <LibJS/Object.h>
+
+namespace JS {
+
+class NativeFunction final : public Object {
+public:
+    explicit NativeFunction(AK::Function<Value(Vector<Argument>)>);
+    virtual ~NativeFunction() override;
+
+    AK::Function<Value(Vector<Argument>)>& native_function() { return m_native_function; }
+
+private:
+    virtual bool is_native_function() const override { return true; }
+    virtual const char* class_name() const override { return "NativeFunction"; }
+
+    AK::Function<Value(Vector<Argument>)> m_native_function;
+};
+
+}
diff --git a/Libraries/LibJS/Object.h b/Libraries/LibJS/Object.h
index cb13c4b4ba..626396ff01 100644
--- a/Libraries/LibJS/Object.h
+++ b/Libraries/LibJS/Object.h
@@ -42,6 +42,7 @@ public:
     void put(String property_name, Value);
 
     virtual bool is_function() const { return false; }
+    virtual bool is_native_function() const { return false; }
 
     virtual const char* class_name() const override { return "Object"; }
     virtual void visit_children(Cell::Visitor&) override;