The FXScript Reference

if you have a subroutine such as

on doSomething(string subString, float subFloat, color theColour)
[do something]
end

you can't call it as follows

doSomething("hello", 1.234, {255,255,0,0}}

calling the string like this will result in a type-mismatch error. instead you have to pass it pre-declared variables that have had their values assigned eg:

string theString;
float, theFloat;
color theColour;

theString="hello"
theFloat = 1.234
theColour = {255,255,0,0}

doSomething(theString, theFloat, theColour);

the subroutine has to be defined in the code before it is called, or you'll get a look of blank incomprehension from the parser.

This one will not result in type errors:

on doSomething(string a_string, value a_value)
...
end;

...

doSomething("the text", 1.2);

Although I can't find a way to be able to pass other types as a constant. (It did not mind the string argument, actually)

Subroutines are limited to 15 parameters. If a subroutine declaration has more than 15 parameters, FCP crashes immediately upon running the script. I haven't found this documented anywhere.

This works [declarations are one line]:
on ftest(value a1,value a2,value a3,value a4,value a5,value a6,value a7,value a8,value a9,value a10,value a11,value a12,value a13,value a14,value a15)
    //
end

This doesn't:
on ftest(value a1,value a2,value a3,value a4,value a5,value a6,value a7,value a8,value a9,value a10,value a11,value a12,value a13,value a14,value a15, value a16)
    //
end