finished let forms

Signed-off-by: Ava Hahn <ava@aidanis.online>

src/stl.rs

@@ -69,6 +69,16 @@ pub fn static_stdlib(syms: &mut SymTable) -> Result<(), String> {
         },
     );
 
+    syms.insert(
+        "let".to_string(),
+        Symbol {
+            name: String::from("let"),
+            args: Args::Infinite,
+            conditional_branches: true,
+            value: ValueType::Internal(Rc::new(control::let_callback)),
+        },
+    );
+
     Ok(())
 }