hi, first here is why i think n+k patterns are problematic; 1) they lead to some parsing awkwardness (e.g. when n+k pattern bindings are involved, but those don'treally make much sense anyways) 2) in haskell as it is, patterns are associated with algebraic datatypes, and n+k patterns may erronously suggest that all numbers are such for the rest, apologies if i appear to be ranting :-) Henk-Jan van Tuyl wrote:
1) It takes no effort, once you are use to it, to code without n+k patterns;
this does not seem like a good argument. there are many other features like that in haskell. for example, going by that we could remove lambda abstractions (i am not saying we should)
on the other hand, when you often use these patterns, you might spend hours debugging an endless looping program.
how do n+k patterns lead to looping programs?
If you are working under high pressure in a large project, chances are, that the testing departement will find your bug and write a bug report (or worse, the customer might find it). Report handling and bug solving costs an enormous amount of money. This has resulted in the "clean room" approach for software design: prevent bugs rather than solve them. See also Finnagle's Law.
i find this reasoning backward. i agree (of course!) that we should write programs without bugs. i find it strange that people often motivate that, by telling me that bugs cost a lot of money for some company. if companies happened to make money out of bugs (and some do), would it then be ok to write buggy software? i guess it all comes down to what one takes as primary -- writing good software, or making money.
2) It is likely, that n+k patterns dissapear in the next Haskell standard. If you don't like to rewrite, test and debug all your software every few years, don't use any language/compiler features that are likely to dissapear. This is another thing that might cost companies a lot of money.
i didn't know anyone is working on a next haskell standard. have n+k patterns been made obsolete? -iavor -- ================================================== | Iavor S. Diatchki, Ph.D. student | | Department of Computer Science and Engineering | | School of OGI at OHSU | | http://www.cse.ogi.edu/~diatchki | ==================================================