Re: [Haskell] insufficiently laziness@pattern -- more counterintuitive stuff

tis 2004-03-30 klockan 17.30 skrev S. Alexander Jacobson:

I would assume that this function:

foo list@(h:t) = list

is equivalent to

foo list = list where (h:t)=list

But passing [] to the first generates an error even though h and t are never used! Passing [] to the second works just fine.

You can write this as

foo' list@(~(h:t)) = list

foo' [] will evaluate to []. The H98 report calls it an "irrefutable pattern", IIRC. Regards, Martin