On 27 January 2006 10:50, John Hughes wrote:
I'd be fairly horrified at the removal of ~ patterns. I've used them to fix very serious space-leaks that would have been awkward to fix in any other way.
You use them to *fix* space leaks? Can you give an example? I'm genuinely surprised and interested - I don't think I've ever seen a case of this before, but I've seen the opposite many times (lazy pattern matching being the cause of space leaks). The reasoning behind removing ~ patterns, for me, is that the number of times they are used doesn't justify stealing the ~ symbol and the extra complexity in the language design, when you can get the same effect with let bindings. With pattern guards there's even less justification for keeping ~, eg. f (a, ~(x:xs)) = e turns into f (a,b) | let (x:xs) = b = e you can translate any equation this way. I would probably write the second form in prefernce to the first, because the strict pattern matches are clearly separated from the lazy. I admit to being slightly biased though, in the type of Haskell programming I do I have almost never needed to use ~. Very occasionally when doing cyclic programming, is all. Cheers, Simon