1 files changed, 31 insertions, 11 deletions

diff --git a/src/type/mod.rs b/src/type/mod.rs
index 37081a1..aeeff93 100644
--- a/src/type/mod.rs
+++ b/src/type/mod.rs
@@ -48,6 +48,7 @@ pub enum TypeError {
     OtherError
 }
 
+use Type::*;
 
 impl Type {
     /// Tests if the type has no variable types.
@@ -56,21 +57,40 @@ impl Type {
     /// ```rust
     /// use melisp::r#type::{*, Type::*, TypeError::*, util::*};
     ///
-    /// assert!(Integer.is_concrete());
-    /// assert!(!VarType("a".to_string()).is_concrete());
+    /// assert_eq!(Integer.is_concrete(), Ok(()));
+    /// assert_eq!(
+    ///     VarType("a".to_string()).is_concrete(),
+    ///     Err("a".to_string())
+    /// );
     ///
-    /// assert!(arr(Integer, Integer).is_concrete());
-    /// assert!(!arr(VarType("b".to_string()), Integer).is_concrete());
+    /// assert_eq!(arr(Integer, Integer).is_concrete(), Ok(()));
+    /// assert_eq!(
+    ///     arr(VarType("b".to_string()), Integer).is_concrete(),
+    ///     Err("b".to_string())
+    /// );
     ///
-    /// assert!(
-    ///     List(vec![Integer, Integer, arr(Integer, Integer)]).is_concrete()
+    /// assert_eq!(
+    ///     List(vec![Integer, Integer, arr(Integer, Integer)]).is_concrete(),
+    ///     Ok(())
     /// );
-    /// assert!(
-    ///     !List(vec![Integer, VarType("a".to_string()), Integer])
-    ///         .is_concrete()
+    /// assert_eq!(
+    ///     List(vec![Integer, VarType("a".to_string()), Integer])
+    ///         .is_concrete(),
+    ///     Err("a".to_string())
     /// );
     /// ```
-    pub fn is_concrete(&self) -> bool {
-        todo!()
+    pub fn is_concrete(&self) -> Result<(), String> {
+        match self {
+            Integer => Ok(()),
+            Arrow(a, b) => b.is_concrete().and_then(|_ok| a.is_concrete()),
+            List(v) => {
+                let mut res = Ok(());
+                for t in v {
+                    res = res.and_then(|_ok| t.is_concrete());
+                }
+                res
+            },
+            VarType(s) => Err(s.clone()),
+        }
     }
 }