ApplicativeDo: Pattern matching on a bind forces a Monad constraint
Pattern matching on a bind in 8.2.1 confuses ApplicativeDo, and causes the type to have a Monad constraint where a Functor constraint would suffice.
In GHC 8.0:
> :set -XApplicativeDo
> :t \x -> do { (a, _) <- x; pure (a+1) }
\x -> do { (a, _) <- x; pure (a+1) }
:: (Num b, Functor f) => f (b, t) -> f b
In GHC 8.2:
> :set -XApplicativeDo
> :t \x -> do { (a, _) <- x; pure (a+1) }
\x -> do { (a, _) <- x; pure (a+1) }
:: (Num b1, Monad m) => m (b1, b2) -> m b1
Trac metadata
Trac field | Value |
---|---|
Version | 8.2.1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |