Andrew Gibiansky
I am strongly against this, as sometimes you *do* want to use fromJust. For example:
What people want isn’t necessarily good language design.
1. Quick and dirty scripting/examples where you don't care about error-proofing your work and just want it to be done quickly. In that context, fromJust is a good function.
but you can have your own library that contains “fromMaybe undefined” as well as all the other quick and dirty functions useful for one-off programmes.
2. You know by construction that it is a Just constructor. This is usually not a good design, but sometimes it's useful. Writing an (error "fromJust") is possible, but annoying.
Programming languages accrue all sorts of bad practices from that sort of argument. Good Haskell programming involves making the type system move as many errors as possible from run time to compile time.
(That said, I do wish that `head` and `tail` were replaced by `headMay` and `tailMay`, which you could then use with `fromJust` if you wanted to. But that's another discussion for adding things from `safe` to `base`, unrelated...)
I’m with you on that. So I’m +1 on the proposal. -- Jón Fairbairn Jon.Fairbairn@cl.cam.ac.uk