exported pattern matching

[S.J.Thompson]

Jim - it's worth looking  at the proposal for views, proposed by Warren
Burton et al, accessible from

  http://haskell.galois.com/cgi-bin/haskell-prime/trac.cgi/wiki/Views


regards

Simon T



On Thu, 9 Feb 2006, Jim Apple wrote:

> Sometimes I'd like to use a smart constructor but have pattern
> matching as well. There has been talk elsewhere of allowing export of
> data constructors for /matching/ but not for /construction/:
>
> --------module One---------
> data Picky a = Nil | One a
> picky x = if some_complex_thing x then One x else Nil
> --------module Two---------
> f x = g $ picky x
>
> g Nil y = y
> g (One x) y = x
>
> h Nil = One True
> -----------------
>
> I'd like for the function g to be fine and the function h to get a
> complaint like "error: no constructor 'One'" or, even better, "error:
> 'One' only works in pattern matching"
>
> Jim
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