Question

Is there a programming language (may be a concept or research paper), which allows
a polymorphism over function/method arguments values? Kind of:

function factorial(int value > 0){ /* code here */}
function factorial(int value == 0){ /* code here */}
function factorial(int value < 0){ /* code here */}

And, what is the official name, if any, for this kind of polymorphism?

Answer 1

I guess what you’re looking for is pattern matching and/or guards. Erlang for instance allows this:

foo(X) when X > 0  -> bar(X);
foo(X) when X == 0 -> baz(X);
foo(X)             -> X.

foo("bar", X) -> bar(X);
foo(42, X)    -> baz(X);
foo(_, X)     -> X.

The former demonstrates the use of guards, the latter is a simple pattern match, where the first argument is either "bar", 42 or anything else. Both techniques can be found in many functional languages.

Just in case you’re not familiar with the syntax, that’s equivalent to (as much as it can be compared):

function foo("bar", x) {
    return bar(x);
}
function foo(42, x) {
    return baz(x);
}
...