Add a convenience function withEnv

[marmistrz]

It's useful when you're storing the environment in a data structure.

[chessai]

I agree that this seems useful. Perhaps others might as well, and chime in.

Can you add a changelog entry?

[andrewthad]

I agree that such a function is useful. However, if it's going be in mtl, I would rather see its monomorphic cousin appear in transformers first. The name feels a little disconnected. The function is closely related to local, and none of the existing reader functions mention with or Env in their name. A few ideas (not that I particularly like any of these): localEnv, localConst, local' (gross), local_.

[chessai]

I agree that such a function is useful. However, if it's going be in mtl, I would rather see its monomorphic cousin appear in transformers first. The name feels a little disconnected. The function is closely related to local, and none of the existing reader functions mention with or Env in their name. A few ideas (not that I particularly like any of these): localEnv, localConst, local' (gross), local_.

This makes sense. An issue should first be opened on transformers then.

[chessai]

btw, perhaps readerM is a good name? because we have

reader :: MonadReader r m => (r -> a) -> m a

so readerM makes a nice contrast, just indicating that the function is monadic:

readerM :: (r -> m a) -> m a
readerM f = ask >>= f

[chessai]

btw, perhaps readerM is a good name? because we have

reader :: MonadReader r m => (r -> a) -> m a

so readerM makes a nice contrast, just indicating that the function is monadic:

readerM :: (r -> m a) -> m a
readerM f = ask >>= f

I had something else in mind when writting this comment. disregard.