Opal (programming language)

Example program

This is an example OPAL program, which calculates the GCD recursively.

Signature file (declaration)

SIGNATURE GCD FUN GCD: nat ** nat -> nat

Implementation file (definition)

IMPLEMENTATION GCD IMPORT Nat COMPLETELY DEF GCD(a,b) == IF a % b = 0 THEN b ELSE IF a-b < b THEN GCD(b,a-b) ELSE GCD(a-b,b) FI FI