Add get function

Author: Tko1

src/environment.rs

@@ -77,6 +77,7 @@ impl Environment {
         let concat_fn = rust_core::ConcatFn {};
         let print_string_fn = rust_core::PrintStringFn {};
         let assoc_fn = rust_core::AssocFn {};
+	let get_fn = rust_core::GetFn {};
         // Hardcoded fns
         let lexical_eval_fn = Value::LexicalEvalFn {};
         // Hardcoded macros
@@ -116,6 +117,7 @@ impl Environment {
         );
         environment.insert(Symbol::intern("nth"), nth_fn.to_rc_value());
 	environment.insert(Symbol::intern("assoc"), assoc_fn.to_rc_value());
+	environment.insert(Symbol::intern("get"), get_fn.to_rc_value());
         environment.insert(Symbol::intern("concat"), concat_fn.to_rc_value());
         environment.insert(
             Symbol::intern("print-string"),

src/rust_core.rs

@@ -289,3 +289,31 @@ impl IFn for AssocFn {
         Value::Nil
     }
 }
+
+// General assoc fn; however,  currently just implemented
+// for our one map type, PersistentListMap
+#[derive(Debug, Clone)]
+pub struct GetFn {}
+impl ToValue for GetFn {
+    fn to_value(&self) -> Value {
+        Value::IFn(Rc::new(self.clone()))
+    }
+}
+impl IFn for GetFn {
+    fn invoke(&self, args: Vec<Rc<Value>>) -> Value {
+        if args.len() != 2  { 
+            return Value::Condition(format!(
+                "Wrong number of arguments given to function (Given: {}, Expected: 2)",
+                args.len()
+            ));
+	}
+    
+	if let Value::PersistentListMap(pmap) = &*(args.get(0).unwrap().clone()) {
+	    let key = args.get(1).unwrap();
+	    return pmap.get(key).to_value();
+        }
+	// @TODO add error in here with erkk's new error tools 
+
+        Value::Nil
+    }
+}