Hi
Cons: Makes the simplifier slightly more complex - but I hope not by much!
And it doesn't work for my case -- I'd really want length as a compile time constant.
Could you elaborate on what kind of rules you think we could write with the ability to get the head?
One of my ideas was some RULES that expand: test x | "neil" `isPrefixOf` x = ... | "ned" `isPrefixOf` x = ... And obtains direct pattern-matching code. I have a lazy continuation-based parsing library which could use this extensively. See my other ongoing thread on this mailing list for more details of where this is going.
The rule I'd like to write is:
"pack/packAddress" pack (unpackCString addr) = ByteString (length# xs) 0 addr
That requires Proposal 2, so needs to have an API defined -- including length# and some others. Out of curiosity, how much performance boost would this give in ByteString?
That sounds great! Please let's have a chat before you sail in -- I have a good idea where to put this.
Simon: I will email you in a couple of weeks to discuss it. Thanks Neil