Implement setting global values (#93)

* Use builder pattern to create interpreter

* Add method to initialize global object

* Run rustfmt to fix CI build

* Run rustfmt beta to fix CI build

src/lib/exec.rs

@@ -32,19 +32,18 @@ pub struct Interpreter {
     environment: LexicalEnvironment,
 }
 
+/// Builder for the [`Interpreter`]
+///
+/// [`Interpreter`]: struct.Interpreter.html
+#[derive(Debug)]
+pub struct InterpreterBuilder {
+    /// The global object
+    global: Value,
+}
+
 impl Executor for Interpreter {
     fn new() -> Self {
-        let global = ValueData::new_obj(None);
-        object::init(&global);
-        console::init(&global);
-        math::init(&global);
-        array::init(&global);
-        function::init(&global);
-        json::init(&global);
-        string::init(&global);
-        Self {
-            environment: LexicalEnvironment::new(global.clone()),
-        }
+        InterpreterBuilder::new().build()
     }
 
     #[allow(clippy::match_same_arms)]
@@ -376,6 +375,38 @@ impl Executor for Interpreter {
     }
 }
 
+impl InterpreterBuilder {
+    pub fn new() -> Self {
+        let global = ValueData::new_obj(None);
+        object::init(&global);
+        console::init(&global);
+        math::init(&global);
+        array::init(&global);
+        function::init(&global);
+        json::init(&global);
+        string::init(&global);
+
+        Self { global }
+    }
+
+    pub fn init_globals<F: FnOnce(&Value)>(self, init_fn: F) -> Self {
+        init_fn(&self.global);
+        self
+    }
+
+    pub fn build(self) -> Interpreter {
+        Interpreter {
+            environment: LexicalEnvironment::new(self.global.clone()),
+        }
+    }
+}
+
+impl Default for InterpreterBuilder {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl Interpreter {
     /// https://tc39.es/ecma262/#sec-call
     fn call(&mut self, f: &Value, v: &Value, arguments_list: Vec<Value>) -> ResultValue {

src/lib/js/value.rs

@@ -1,7 +1,7 @@
 use crate::js::{
     function::{Function, NativeFunction, NativeFunctionData},
     object::{Object, ObjectKind, INSTANCE_PROTOTYPE, PROTOTYPE},
-    property::Property
+    property::Property,
 };
 use gc::{Gc, GcCell};
 use gc_derive::{Finalize, Trace};
@@ -853,5 +853,4 @@ mod tests {
         assert_eq!((-1.0).to_value().is_true(), true);
         assert_eq!(NAN.to_value().is_true(), false);
     }
-
 }

src/lib/syntax/lexer.rs

@@ -894,5 +894,4 @@ mod tests {
         assert_eq!(lexer.tokens[0].data, TokenData::NumericLiteral(1.0));
         assert_eq!(lexer.tokens[1].data, TokenData::Punctuator(Punctuator::Dot));
     }
-
 }