add more unit tests for function calls

src/func.rs

@@ -32,9 +32,9 @@ pub struct ExternalOperation {
     // TODO: Intermediate evaluation to simplify branches with no argument in them
     //       Simplified branches must not have side effects.
     // TODO: Apply Memoization?
-    ast: Ast,
+    pub ast: Ast,
     // list of argument string tokens
-    arg_syms: Vec<String>
+    pub arg_syms: Vec<String>
 }
 
 /* A stored function may either be a pointer to a function
@@ -94,11 +94,16 @@ pub fn func_call(
 
     match &called_func.args {
         Args::Lazy(num) => {
-            if *num < 0 {
-            }
-
-            if !(*num == (list_len(n_args.clone()) as i128 - 1)) {
-                return Err(format!("expected {} args in call to {}", num, called_func.name))
+            let called_arg_count = list_len(n_args.clone()) as i128;
+            if *num > -1 && (*num != called_arg_count) {
+                return Err(
+                    format!(
+                        "expected {} args in call to {}. Got {}.",
+                        num,
+                        called_func.name,
+                        called_arg_count
+                    )
+                )
             }
         },
 
@@ -151,10 +156,13 @@ pub fn func_call(
     match &called_func.function {
         Operation::Internal(f) => Ok((f)(n_args, vars, funcs)),
         Operation::External(f) => {
+
             for n in 0..f.arg_syms.len() {
+                let iter_arg = list_idx(n_args.clone(), n as u128);
+
                 vars.borrow_mut().insert(
                     f.arg_syms[n].clone(),
-                    Rc::new(list_idx(n_args.clone(), n as u128))
+                    Rc::new(iter_arg)
                 );
             }