Jon Fairbairn
Which leads me to my own question: in current implementations, if I have a data structure containing a function (D f, say), and from it I generate anoter (D (flip f)), and then later (D (flip (flip f))) and so on, do the flips get reduced (to nothing if there's an even number of them) when the field of D is evaluated?
No, not as far as I can see, unless there are opportunities for static inlining (and therefore compile-time reduction). AIUI, the application of flip needs to see three arguments before it can be evaluated. Thus, in this example: let f'' = flip (flip f) appf = f'' 0 in [appf 1, appf 2, appf 3] the code for flip will run six times, whereas here: let f'' = flip (flip f) appf = f'' 0 1 in [appf 2, appf 3, appf 4] the code for flip is run only twice. The difference in the examples is that flip is only partially applied in the first case, but fully saturated in the second. At any rate, I think this is how it works in nhc98. Regards, Malcolm