Dear Devs,
I've tried to ask this in the ($) thread, but it was totally offtopic
there and I was ignored just as I deserved :-)
Consider the following example.
wojtek@Desktop2016:~/src/he$ cat kinds.hs
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE KindSignatures #-}
data K = A | B
f :: (A :: K) -> (B :: K)
f _ = undefined
wojtek@Desktop2016:~/src/he$ /opt/ghc/head/bin/ghc kinds.hs
[1 of 1] Compiling Main ( kinds.hs, kinds.o )
kinds.hs:6:6: error:
• Expected a type, but ‘'A’ has kind ‘K’
• In the type signature:
f :: (A :: K) -> (B :: K)
kinds.hs:6:18: error:
• Expected a type, but ‘'B’ has kind ‘K’
• In the type signature:
f :: (A :: K) -> (B :: K)
As Roman kindly (!) explained to me some time ago, GHC really means
"Expected a type of kind '*' (or '#')..."
Now that GHC is apparently undergoing a major overhaul of its internals,
would it be possible to allow types of various kinds in functions? Would
it make sense? May I file a ticket?
--
Kind regards,
Wojtek Narczynski
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