caselib

This is a tiny header which adds a Haskell/ML-likepattern matching case statement to C++.

Usage

For example, implementing the Ackermann function

A(m,n) = case (0,n) = n + 1
            | (m,0) = A(m-1,1)
            | (m,n) = A(m - 1, A(m, n-1)),

is as simple as

#include <case.h>
int A(int m, int n) {
    return CASE((m, n), (0, n) = n + 1,
                        (m, 0) = A(m - 1, 1),
                        (m, n) = A(m - 1, A(m, n-1)),
                        -1); // Default return value, if no cases match
}

which expands into

int A(int m, int n) {
    return (m == 0 && n == n) ? n + 1 :
           (m == m && n == 0) ? A(m - 1, 1) :
           (m == m && n == n) ? A(m - 1, A(m, n-1)) :
           -1;