On Mon, 7 Jul 2008 02:57:25 -0700 (PDT), fero <[EMAIL PROTECTED]> wrote:
If you are interested in logic programming in a language with some similarity to Haskell, you might also wish to investigate the strongly typed logic programming language Godel (see http://www.cs.bris.ac.uk/~bowers/goedel.html). When I first saw an example of the code, I was surprised that, unlike Prolog, the language was strongly typed, and supported modules, and (albeit very loosely) resembled Haskell, except that it was a logic programming language. Here is an example of a program in Godel to compute a greatest common divisor (note the strong typing and usage of a module system) (see http://www.cs.bris.ac.uk/~bowers/goedel-example.html): MODULE GCD. IMPORT Integers. PREDICATE Gcd : Integer * Integer * Integer. Gcd(i,j,d) <- CommonDivisor(i,j,d) & ~ SOME [e] (CommonDivisor(i,j,e) & e > d). PREDICATE CommonDivisor : Integer * Integer * Integer. CommonDivisor(i,j,d) <- IF (i = 0 \/ j = 0) THEN d = Max(Abs(i),Abs(j)) ELSE 1 =< d =< Min(Abs(i),Abs(j)) & i Mod d = 0 & j Mod d = 0. According to the home page for the language, > Go"del is a declarative, general-purpose programming language in the family > of > logic programming languages. It is a strongly typed language, the type system > being based on many-sorted logic with parametric polymorphism. It has a > module system. Go"del supports infinite precision integers, infinite > precision > rationals, and also floating-point numbers. It can solve constraints over > finite > domains of integers and also linear rational constraints. It supports > processing > of finite sets. It also has a flexible computation rule and a pruning > operator > which generalises the commit of the concurrent logic programming languages. > Considerable emphasis is placed on Go"del's meta- logical facilities which > provide > significant support for meta-programs that do analysis, transformation, > compilation, verification, debugging, and so on. -- Benjamin L. Russell >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. > >Thanks >Fero _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
