Re: Using reduce() with tuples created by zip()

[bearophile]

alias sum(T) = curry!(reduce!q{a + b}, cast(T)0);

double euclidDistance(double[] xs, double[] ys)
in {
    assert(xs.length == ys.length);
} body {
    return zip(xs, ys)
           .map!(xy => (xy[0] - xy[1]) ^^ 2)
           .sum!double
           .sqrt;
}
void main() {
    auto xs = [0.0,  1.0, 0.1];
    auto ys = [1.0, -1.0, 0.0];
    euclidDistance(xs, ys).writeln;
}

In D functions are written in camelCase like euclidDistance, 
instead of euclid_distance.

Function pre-conditions and post-conditions are generally better 
put in the pre and post part of functions.

I have defined a sum because it's a generally useful function, 
but it's a toy because it assumes cast(T)0 as the identity 
element of the monoid with the plus operator.

Bye,
bearophile