1 files changed, 7 insertions, 5 deletions

diff --git a/src/lisp/expr.rs b/src/lisp/expr.rs
index 045991e..6f5b139 100644
--- a/src/lisp/expr.rs
+++ b/src/lisp/expr.rs
@@ -26,13 +26,17 @@ pub enum Arity {
 }
 
 impl Arity {
-    pub fn check<T>(self, args: &[T]) -> bool {
-        match self {
+    pub fn check<T>(self, args: &[T]) -> Result<(), LispError> {
+        if !match self {
             Arity::Exact(a) => args.len() == a,
             Arity::Atleast(a) => args.len() >= a,
             Arity::Atmost(a) => args.len() <= a,
             Arity::Range(low, high) => args.len() >= low && args.len() <= high,
             Arity::None => true,
+        } {
+            Err(self.to_error())
+        } else {
+            Ok(())
         }
     }
     pub fn to_error(self) -> LispError {
@@ -49,9 +53,7 @@ pub struct PrimitiveFunc {
 
 impl PrimitiveFunc {
     pub fn call(&self, args: &[LispExpr], app: &mut AppState) -> Result<LispExpr, LispError> {
-        if !self.arity.check(args) {
-            return Err(EvalError::ArgumentCount(self.arity).into());
-        }
+        self.arity.check(args)?;
         (self.closure)(args, app)
     }
 }