On Tue, May 4, 2010 at 12:13 AM, Ivan Miljenovic <ivan.miljeno...@gmail.com> wrote: > On 4 May 2010 13:30, Luke Palmer <lrpal...@gmail.com> wrote: >> Here is a contrived example of what I am referring to: >> >> prefac f 0 = 1 >> prefac f n = n * f (n-1) >> >> fac = (\x -> x x) (\x -> prefac (x x)) > > I can't work out how this works (or should work rather); is it meant > to be using church numerals or something (assuming that they have been > made an instance of Num so that - and * work)?
Looks like a variation on H. Curry's fixed-point combinator to me, e.g.: y f = (\x -> f (x x)) (\x -> f (x x)) Which of course is perfectly useful, but not valid in any type system that excludes absurdities. The otherwise-infinite type signature for Y is circumvented by built-in recursion in Haskell (making halting undecidable in the process, unfortunately). - C. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
