[Haskell-cafe] Scrap your rolls/unrolls
dan.doel at gmail.com
Fri Oct 22 07:14:06 EDT 2010
On Friday 22 October 2010 6:37:49 am Max Bolingbroke wrote:
> This is all well and good, but it means when working with data types
> defined in this manner you have to write Roll and unroll everywhere.
> This is tedious :-(
Your discovery is interesting (and I haven't seen it before).
Another solution, though, is SHE. With it, you can write:
data ListF a r = NilF | ConsF a r
newtype List a = Roll (ListF a (List a))
pattern Nil = Roll NilF
pattern Cons x xs = Roll (ConsF x xs)
And not worry about Rolls anymore.
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