[Haskell-beginners] mayBe stuck

[Brent Yorgey]

On Fri, Aug 06, 2010 at 11:15:52AM +0100, Colin Paul Adams wrote:
> >>>>> "Brent" == Brent Yorgey <byorgey at seas.upenn.edu> writes:
> 
>     >> Since Haskell allows programming with partial functions, you
>     >> always have this burden at present.
> 
>     Brent> Yes.  But that doesn't mean there isn't value in the
>     Brent> discipline of avoiding them.  The burden of making sure you
>     Brent> never use fromJust (or head, or ...) is much lighter than the
>     Brent> burden of proving that every such use is safe.
> 
> The burden is knowing whether or not a function is partial. It's that or
> ... that is the problem. This isn't flagged anywhere.

That's a very good point.  But it's the sort of thing you pick up
pretty quickly, I think.  Here are some off the top of my head, for
beginners reading this who might not already know:

  fromJust
  head
  tail
  init
  last
  (!!)

For a fuller list, take a look at the 'safe' package on Hackage [1],
which also provides many different safe alternatives.

-Brent

[1] http://hackage.haskell.org/package/safe