Closed type families don't reduce on data family instances
The following code doesn't compile:
{-# LANGUAGE TypeFamilies #-}
module Tmp where
data family D a
data instance D () = D
type family T a where
T () = ()
T a = Char
try :: T (D ()) ~ Char => ()
try = ()
main :: IO ()
main = return try
giving
Tmp.hs:15:15:
Couldn't match expected type ‘Char’ with actual type ‘T (D ())’
In the first argument of ‘return’, namely ‘try’
In the expression: return try
In an equation for ‘main’: main = return try
Is this a known limitation of closed type families?
Trac metadata
Trac field | Value |
---|---|
Version | 7.10.2 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |