Gertjan Kamsteeg <[EMAIL PROTECTED]> writes: >> You don't have to define cpsfold explicitly recursively since it >> can be expressed in terms of foldr:
Hal Daume III <[EMAIL PROTECTED]> writes: > Is this generally considered good design? [...] Three different attempts at an answer: As with all code-factoring it's in the eye of the beholder. If what you want to do is trace execution in detail, the less factored code is easier to understand. If what you want to do is understand the difference between 5 different recursive traversals of a list, then isolating those differences (by suppressing the invariant fact of recursion) is better. More concretely, some prefer to avoid the recursive formulations because: 1) It is trickier to reason about. Functional programmers (especially Squiggol afficianados) have all kinds of cunning ways to reason about programs written using standard library functions such as foldr. The techniques for reasoning directly about recursive functions are somewhat cruder and harder. 2) The ability to recursivly invoke the function from _anywhere_ in the function body has been compared (with some justification) to the use of goto in unstructured programming. If you buy into this line of reasoning then foldr, scanr, map, etc. are to functional programming as while, repeat and for are to structured programming. [These two points are connected!] And, finally, my personal preference is: - use explicit recursion when I don't understand what I'm doing well enough to know which standard recursive pattern it fits into (because it normally always fits a standard pattern). - use higher-order functions when I know what I'm doing or where setting up the infrastructure for the recursion costs more than coding it directly. -- Alastair Reid Reid Consulting (UK) Ltd _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
