On Mon, 7 Jul 2008, fero wrote:
Hi I have read in one tutorial (I can't find it again, but it was probably either one on ibm, gentle introduction or yaht), that it is possible to define relationships between free variables and the same program can be used to calculate either first variable when second is set or second when first is set. I have understood this as if I set first free variable, run program and write name of second variable and I get result, and vice versa. I don't know if I understood it well. It looks really interesting but I can't figure out how to do it. Is this really possible? (I doubt.) If yes show example please.
Are you talking about logic programming and PROLOG? $ pl # swi-prolog ?- plus(X,2,3). X = 1 ; No ?- plus(1,X,3). X = 2 ; No ?- plus(1,2,X). X = 3 ; No Actually the type system of Haskell is also logic programming. I have implemented a simple kind of logic programming using lazy peano numbers: http://darcs.haskell.org/unique-logic/