Better error message regarding type synonyms and PolyKinds
Followup of https://mail.haskell.org/pipermail/haskell-cafe/2015-July/120505.html
ghci> :set -XPolyKinds
ghci> type Test a = a
ghci> type Huh = Test
<interactive>:6:1:
Type synonym ‘Test’ should have 2 arguments, but has been given 1
In the type declaration for ‘Huh’
(Notice the number of arguments reported)
Jonas Scholl at haskell-cafe suggested that the additional invisible argument is a kind argument, which indeed looks to be the case, as he demonstrated:
Prelude> :set -XPolyKinds -XDataKinds -XKindSignatures
Prelude> type Test a = a
Prelude> type Huh a = Test (a :: Bool)
Prelude> type Bar = Huh
<interactive>:5:1:
Type synonym ‘Huh’ should have 1 argument, but has been given none
In the type declaration for ‘Bar’
A better error message may be desirable here.
Trac metadata
Trac field | Value |
---|---|
Version | 7.10.1 |
Type | FeatureRequest |
TypeOfFailure | OtherFailure |
Priority | low |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |