OpenEuphoria

1. clearing "return info" in a function

• Posted by eddo May 30, 2013
• 1282 views

I hope someone understands this. I'm deep inside a function (normally returns a value), and the situation is I want to call another function JUST AS IF I MYSELF HAD NOT BEEN CALLED AS A FUNCTION, which normally returns a value (and has return info on the stack or somewhere), so this "pending return stuff" is cleared permanently and the program won't build to an eventual crash (stack overflow or something that would happen from the "return" never happening). I hesitate to ask because I can imagine everyone saying "OH for Pete's sake! Just do it some other way that doesn't have that problem!" Well, maybe I could, but a little thinking tells me that it would be VERY COMPLEX as far as i know, to do so. It would be SO EASY to do what I want (and useful, I think enough so it could be a feature, being inside a function and being able to cancel the "function action" of always returning a value to whatever called it). At least I figured it'd be worth posting a question about, as it might be easy to do something like this from what little I know.

3. Re: clearing "return info" in a function

• Posted by jimcbrown (admin) May 30, 2013
• 1295 views

I wonder if it would work with the translator, assuming you returned integers and had a C compiler that supported it.

5. Re: clearing "return info" in a function

• Posted by PeteE May 30, 2013
• 1293 views

I have to eat my words, since I didn't try this beforehand:

function foo(integer x) 
        if x = 0 then 
                return 0 
        end if 
        return foo(x-1)   
end function 
 
? foo(1000000000) 

You'd expect this to blow the stack, but it runs fine in the interpreter. And the translated code shows goto instead of recursive call! Seems Euphoria IS smart enough to detect and optimize tail calls - great job guys!

int _1foo(int _x_142) 
{ 
    int _9 = NOVALUE; 
    int _0, _1, _2; 
     
L1:  
    if (!IS_ATOM_INT(_x_142)) { 
        _1 = (long)(DBL_PTR(_x_142)->dbl); 
        DeRefDS(_x_142); 
        _x_142 = _1; 
    } 
 
    /**         if x = 0 then*/ 
    if (_x_142 != 0) 
    goto L2; // [7] 18 
 
    /**                 return 0*/ 
    return 0; 
L2:  
 
    /**         return foo(x-1)*/ 
    _9 = _x_142 - 1; 
    if ((long)((unsigned long)_9 +(unsigned long) HIGH_BITS) >= 0){ 
        _9 = NewDouble((double)_9); 
    } 
    _0 = _x_142; 
    _x_142 = _9; 
    DeRef(_0); 
    DeRef(_9); 
    _9 = NOVALUE; 
    goto L1; // [24] 1 
    ; 
} 

7. Re: clearing "return info" in a function

• Posted by Insolor May 31, 2013
• 1184 views

I do remember it was noted somewhere, since I tested this feature as soon I learned about it.
I just searched 'tail recursion' phrase and found it here http://openeuphoria.org/wiki/view/ChangesFor4_0b2.wc