Allow switching to different monads in GHCi
GHCi can evaluate individual IO actions, e.g.
ghci> writeFile "foo.txt" "bar"
ghci> readFile "foo.txt"
barbut, as far as I know, this doesn't extend to other monads. Instead you have to compose an entire computation and then run it with the standard eliminators, e.g.
ghci> evalState 0 (put 1 >> get)
1It would be quite nice if we could tell GHCi to temporarily jump into a different top-level monad, e.g.
-- we start in IO as usual
ghci> :monad runState 0
-- now we're in `State Int` with the initial state set to 0
ghci> put 1
-- we can evaluate individual State actions without the ceremony of `runState`,
-- and having to track the updated state ourselves between actions
ghci> get
1
ghci> :monad IO
-- now we're back in IOI'm not sure how feasible this is (it seems tricky), but it would provide a very nice UX for GHCi in the context of larger Haskell applications.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.11 |
| Type | FeatureRequest |
| TypeOfFailure | OtherFailure |
| Priority | low |
| Resolution | Unresolved |
| Component | GHCi |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | hvr |
| Operating system | |
| Architecture |