lambda cube

content/posts/the-lambda-cube/WhatIThoughtDataKindsDid.hs

@@ -0,0 +1,19 @@
+{-# LANGUAGE DataKinds #-}
+module WhatIThoughtDataKindsDid where
+
+data Ty
+    = A {field1 :: Int}
+    | B {field2 :: Int}
+
+someFunctionTakingB :: 'B -> Int
+someFunctionTakingB = field2
+
+{-
+WhatIThoughtDataKindsDid.hs:8:24: error:
+    • Expecting one more argument to ‘'B’
+      Expected a type, but ‘'B’ has kind ‘Int -> Ty’
+    • In the type signature: someFunctionTakingB :: 'B -> Int
+  |
+8 | someFunctionTakingB :: 'B -> Int
+  |                        ^^
+ -}