On Tue, 2004-06-22 at 14:17, Tomasz Zielonka wrote:
On Tue, Jun 22, 2004 at 01:52:44PM +0100, Malcolm Wallace wrote:
Same again. Try addHeight h E = h `seq` h
which, although it looks bizarre, actually forces the evaluation of h, whilst simply returning it does not.
That contradicts my intution for seq. I would read it as "h is forced before h is forced", and I would think that (h `seq` h) is equivalent to h.
I think a better intuition is that "h is forced before h is *returned*". You can return a value without that value being forced to head normal form. In fact this is the ordinary case. Values are only 'forced' when you pattern match on them (or if you use seq), and even then only when the result of the pattern match is used. Duncan