Re: [Haskell-cafe] Pattern matching articles/explanations

Hi

So what I noticed that "A Gentle Introduction to Haskell" mentioned that wild-cards are useful in constructors. For example:

head (x:_) = x

So, does that offer any performance benefits over:

head (x:xs) = x

No. They are exactly the same. _ simply means "a new unique name".

Or is it primarily to indicate to the coder that xs is useless?

Yes

I get the impression it has a very similar meaning to the irrefutable pattern in regards to not evaluating it when the function is called. Or am I way off?

Way off :-) Nothing to do with irrefutable patterns, or demand of evaluation, its got two uses: 1) Indicate to the reader that this argument is never used 2) Save you coming up with a name for the argument Thanks Neil