Looking for an elegant coding idiom.

johnm@v...
 Andrew Conway
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Date:  19950828 (14:10) 
From:  Andrew Conway <arc@l...> 
Subject:  Re: Looking for an elegant coding idiom. 
>CAML is a very elegant language and I am curious to hear of any >elegant coding idioms. I am especially curious to hear of any elegant >solutions to deal with some nuisance code of mine. I once solved this >problem in C. This may be holding me back from an elegant CAML >solution. It may be that there is no "best" style or solution but any >suggestions you have are appreciated. > >I am placing rectangular objects in the plane. There are 8 orthogonal >orientations and they are: > >>type orient = >> R0 >>  R90 >>  R180 >>  R270 >>  MY (* mirrored about the y axis *) >>  MX >>  MXR90 (* mirrored about the x axis and then rotated *) >>  MYR90 >> ;; >Given an orientation it is useful to be able to compose it with >another orientation. A transliteration from C looks something like > >> [ rotation > ordinal > look up table (messy) ] Since you have a group consisting of a rotation r, r^4=I, and a reflection, f^2=I satisfying rf = fr^{1}, one could use the following type definition type orient = Unreflected of int (* The integer is a number 03 or rotations *)  Reflected of int (* The integer is a number 03 or rotations *) ;; let mod4 x = (x+4) mod 4;; (* works for 4<=x<= big number *) let composeorient = fun  (Unreflected n) (Unreflected m) > Unreflected (mod4 (n+m))  (Reflected n) (Unreflected m) > Reflected (mod4 (n+m))  (Unreflected n) (Reflected m) > Reflected (mod4 (mn))  (Reflected n) (Reflected m) > Unreflected (mod4 (mn)) ;; It dies have the disadvantage of requiring more memory, but there are lots of other nice things that one can do with such a representation. Andrew.