better rendering for type errors and evaluation

1 files changed, 13 insertions, 0 deletions

diff --git a/lambda-calcul/haskell/test/Minilang/REPLSpec.hs b/lambda-calcul/haskell/test/Minilang/REPLSpec.hs
index 4eb3f4d..f6279c1 100644
--- a/lambda-calcul/haskell/test/Minilang/REPLSpec.hs
+++ b/lambda-calcul/haskell/test/Minilang/REPLSpec.hs
@@ -23,6 +23,19 @@ spec = parallel $
                      "y : b"
                    ]
 
+    it "defaults to try to typecheck terms" $ do
+      let out =
+            withInput
+              [ "(let ((Succ (lam (n z s) (s n))) \
+                \ (Zero (lam (z s) z))) \
+                \ (Succ (Succ Zero)))"
+              ]
+
+      out
+        `shouldBe` [ "Bye!",
+                     "Cannot unify type variable f with type (e -> f -> e) -> e due to circularity: The variable already occurs in the type."
+                   ]
+
     it "shows error when trying to load a non-existent file" $ do
       withInput [":load foo"]
         `shouldBe` [ "Bye!",