On Thu, Jun 06, 2013 at 05:27:11PM -0700, Frerich Raabe wrote:
Hi,
is there an existing (or conventional) way to model lists of one or more items? I often deal with functions with don't make sense with empty lists, and the caller already verified that the lists are not empty. So to avoid getting warnings from ghc, I'd like to have a dedicated type for this case.
I could do something like
data List a = Singleton a | Cons a (List a)
but before I go ahead I wonder: is there an existing Haskell package for this? Maybe even with prettier names than what I wrote above, and convenient functions for transforming from/to plain [] lists? It would probably be straightforward to write it myself, but because of that, I suspect that somebody else already did it. :-)
Yes, this exists in the semigroups package: http://hackage.haskell.org/packages/archive/semigroups/0.9.2/doc/html/Data-L... -Brent