function_fib.chr

:- module(function_fib, [compute_fib/2]).
:- chr_constraint compute_fib/2.
:- function fib/1.

fib(0) -> 0.
fib(1) -> 1.
fib(N) | N > 1 -> fib(N - 1) + fib(N - 2).

compute_fib(N, R) <=> R is fib(N).