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"
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