22 Oct
2010
22 Oct
'10
7:14 a.m.
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. -- Dan http://personal.cis.strath.ac.uk/~conor/pub/she/