On Jan 10, 2008 8:39 PM, apfelmus [EMAIL PROTECTED] wrote:
Victor Nazarov wrote:
Yes, there is: you can use a zipper
http://en.wikibooks.org/wiki/Haskell/Zippers
Here's how:
data Branch v = AppL (Term v)
| AppR (Term v)
| Lamb v
type Context
Victor Nazarov wrote:
import Control.Monad.Writer
-- use a difference list or something for better performance
type Trace v = [Zipper v]
whnf :: Term v - Writer (Trace v) (Term v)
whnf t = whnf' ([],t)
where
whnf' (AppL e':cxt, Lam x e) = tell (cxt, App (Lam x e)
