Tags: eunikolsky/podtime
Tags
[DOESN'T BUILD] Reduce instance boilerplate with lifting transformers'
Note: this works in GHC, but fails to compile with GHCi! This is really
bizarre.
```
~/haskell/podtime/program/LiftMonadModTimeT.hs:14:9-42: error:
Illegal datatype context (use DatatypeContexts): (forall i.
Monad i => Monad (t i)) =>
|
14 | newtype (forall i. Monad i => Monad (t i)) => LiftMonadModTimeT t m a = LiftMonadModTimeT (t m a)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
~/haskell/podtime/program/LiftMonadDurationT.hs:14:9-42: error:
Illegal datatype context (use DatatypeContexts): (forall i.
Monad i => Monad (t i)) =>
|
14 | newtype (forall i. Monad i => Monad (t i)) => LiftMonadDurationT t m a = LiftMonadDurationT (t m a)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```
Enabling `DatatypeContexts` complains about:
```
-XDatatypeContexts is deprecated: It was widely considered a misfeature, and has been removed from the
Haskell language.
```
[DOESN'T BUILD] Reduce instance boilerplate with lifting transformers
Note: this works in GHCi, but fails to compile with GHC!
```
~/haskell/podtime/program/LiftMonadDurationT.hs:15:92: error:
• Couldn't match kind ‘* -> *’ with ‘*’
Expected kind ‘* -> * -> *’, but ‘t’ has kind ‘(* -> *) -> * -> *’
• In the first argument of ‘LiftMonadDurationT’, namely ‘t’
In the first argument of ‘MonadDuration’, namely
‘(LiftMonadDurationT t m)’
In the instance declaration for
‘MonadDuration (LiftMonadDurationT t m)’
|
15 | instance (MonadDuration m, MonadTrans t, Monad (t m)) => MonadDuration (LiftMonadDurationT t m) where
| ^
~/haskell/podtime/program/LiftMonadDurationT.hs:15:94: error:
• Expecting one more argument to ‘m’
Expected a type, but ‘m’ has kind ‘* -> *’
• In the second argument of ‘LiftMonadDurationT’, namely ‘m’
In the first argument of ‘MonadDuration’, namely
‘(LiftMonadDurationT t m)’
In the instance declaration for
‘MonadDuration (LiftMonadDurationT t m)’
|
15 | instance (MonadDuration m, MonadTrans t, Monad (t m)) => MonadDuration (LiftMonadDurationT t m) where
| ^
```
PreviousNext