| Gödel | |
| Paradigm: | declarative, logic |
| Year: | 1992 |
| Designer: | John Lloyd & Patricia Hill |
| Developer: | John Lloyd & Patricia Hill |
| Latest Release Version: | 1.5 |
| Typing: | strong |
| Dialects: | Gödel with Generic (Parametrised) Modules |
| Operating System: | Unix-like |
| License: | Non-commercial research/educational use only |
| Website: | https://www.cs.unipr.it/~hill/GOEDEL/expgoedel.html |
Gödel is a declarative, general-purpose programming language that adheres to the logic programming paradigm. It is a strongly typed language, the type system being based on many-sorted logic with parametric polymorphism. It is named after logician Kurt Gödel.
Gödel has a module system, and it supports arbitrary precision integers, arbitrary 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.
Gödel's meta-logical facilities provide support for meta-programs that do analysis, transformation, compilation, verification, and debugging, among other tasks.
The following Gödel module is a specification of the greatest common divisor (GCD) of two numbers. It is intended to demonstrate the declarative nature of Gödel, not to be particularly efficient.The CommonDivisor predicate says that if i and j are not zero, then d is a common divisor of i and j if it lies between 1 and the smaller of i and j and divides both i and j exactly.The Gcd predicate says that d is a greatest common divisor of i and j if it is a common divisor of i and j, and there is no e that is also a common divisor of i and j and is greater than d.
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.