Solution to Functional-Programming Exercise

solution.d

float myFun(SumType!(float, int, string, int[]) a)
{
    import std.functional: pipe;

    return a.match!(
        number => cast(float) number,
        array =>
            array.process
                .common1
                .pipe!((value) {
                    static if (is(typeof(array) == string))
                        return special(array, value);
                    else
                        return value;
                }))
                .common2
    );
}