Generators are a low-level construct in Basic Storm that allows dynamic generation of functions, types or similar things. This construct is the foundation for templates in Basic Storm.

A generator is a function that is called when the system tries to look up a name which does not yet exist. Generators themselves have a name associated with them, but unlike functions, generators do not have any parameters associated to them. Instead, the system asks the generator if it can provide a Named with the given parameters.

A simple generator in Basic Storm looks like this:

genAdd: generate(params) {
    if (params.count != 2)
        return null;

    if (params[0] != params[1])
        return null;

    Value t = params[0];

    BSTreeFn fn(t, SStr("genAdd"), params, ["a", "b"], null);

    Scope scope = rootScope.child(t.getType());

    FnBody body(fn, scope);

    Actual actual;
    actual.add(namedExpr(body, SStr("a"), Actual()));
    actual.add(namedExpr(body, SStr("b"), Actual()));

    body.add(namedExpr(body, SStr("+"), actual));

    return fn;

This generator generates a function named genAdd that adds two parameters of the same type. The declaration (genAdd: generate(params)) indicates that we're declaring a generator named genAdd that receives the parameters in the local variable params. This declaration is more or less equivalent to the function declaration Named? <some name>(Value[] params). The generator is then expected to return a Named object that follows the specification asked for. It is acceptable to alter params by removing references from zero or more parameters, but nothing else. Returning null means that the combination of parameters supplied is not supported by this generator.