On 11/9/06, Udo Stenzel
Jon Fairbairn wrote:
But not all patterns deserve names. To give a reductio-ad-absurdam sort of analogy, suppose someone looked at a lot of C and came to the conclusion that ???for (i=0, i++, ...)??? occurred in 90% of programmes. Were they to reason that it would be worth #defining a macro FORI(...) and using that instead, I suspect that the suggestion would be roundly dismissed.
Well, I presume you actually meant 'for( i=0; ... ; i++ )', an error which would have been avoided by using a macro. Also, a macro would have liberated you of the choice between '++i' and 'i++', where '++i' is often more efficient (at least in C++). And in C++, you're encouraged to use std::for_each anyway, which is the C++ way to spell 'mapM_'. Which would make your point kinda moot, but I'm not really convinced that arguments from a souped up assembly language can be used to make a point about Haskell.
To further belabor the point...In the linux kernel they almost exactly do what Jon was pointing out as a dismissable solution. In the linux kernel they do it for the kernel's data structures. You can find macros galore for manipulating lists and iterating over them[1]. [1] http://isis.poly.edu/kulesh/stuff/src/klist/ Jason