Re: [Haskell-cafe] Re: Debugging partial functions by the rules

dmhouse:

On 16/11/06, oleg@pobox.com wrote:

...

And if we are absolutely positive that the value is (Just x), we can always write maybe (assert False undefined) id v

It should be pointed out that Data.Maybe does export a less well-known function, fromMaybe:

fromMaybe z = maybe z id

This can be used to make the 'maybe X id' case a bit tidier (although technically it's not a save on characters).

How controversial would a proposal to {-# DEPRECATE fromJust #-} be, in favour of: Just _ = x -- which will give you the precise line number maybe (assert False) maybe id fromMaybe It seems to me this is one cause of mysterious newbie errors we could easily discourage, with little harm. -- Don