OpenEuphoria

replace()ing a crash

• Posted by Graeme May 26, 2021
• 920 views

Recently got a hard exit with the 4.1.0 interpreter on win10 migrating an old program from 3.1.1 which I eventually tracked down to a function called replace().

The program was nothing too fancy, just renaming and sorting a bunch of media files, removing filename tags etc.

It was working ok but then suddenly started exiting without any warning or output. After inserting a heap of log and flush to file debug markers and retrying a bunch of times I eventually found the culprit.

I replaced (heh) replace() with this:

 
function replace2(sequence s,object o1,object o2) 
    for x=1 to length(s) do 
        if equal(s[x],o1) then 
            s[x]=o2 
        end if 
    end for 
    return s 
end function 

and the crash stopped.

"Oh", thinks I, "There's a problem in 4.1 with this replace() function", and continued with what I was doing.

But then later on I looked a bit further and discovered that this replace() func was actually one of my own that I had in a library from years ago :facepalm:

The original looks like this:

 
global function replace(object s,object before,object after) 
    if atom(s) then 
	return replace({s},before,after) 
    end if 
    for x=1 to length(s) do 
	if equal(s[x],before) then 
	    s[x]=after 
	end if 
    end for 
    return s 
end function 

Obviously the only difference is that it handles the possibility of someone passing an atom as the haystack via recursion and guarantees a sequence as the return. The nature of that call means the depth can never be greater than two.... if atom(s) then use {s}

This is moot anyway because I got no problem once I used replace2() so it can't have been passing an atom as the first argument or replace2() would have stopped with a type error.

This lead me to believe the the crash could possibly be related to some rare set of circumstances involving passing a sequence as type object for an argument (in this case the first argument) as against passing it as type sequence.

So just when I thought this was all over, I find this:

-- Signature: 
-- <built-in> function replace(sequence target, object replacement, integer start, integer stop=start) 
-- 
-- Description: 
-- replaces a slice in a sequence by an object. 
-- 
-- Parameters: 
--   # ##target## : the sequence in which replacement will be done. 
--   # ##replacement## : an object, the item to replace with. 
--   # ##start## : an integer, the starting index of the slice to replace. 
--   # ##stop## : an integer, the stopping index of the slice to replace. 
-- 
-- Returns: 
-- A **sequence**, which is made of ##target## with the ##start..stop## slice 
-- removed and replaced by ##replacement##, which is spliced in. 

So apparently 4.1 does have a func called "replace()" after all. I'm assuming it would(should?) not have come into play as the global func in my library would have overridden this built-in anyway. Or would it? Not totally up to speed on all the rules involving this stuff. Pretty sure that regardless I shouldn't have ended up with a hard exit.

.

There isn't really any more useful info I can add here. When the crash stopped I renamed and sorted the media files (which was the job at hand), so I don't have the original input from when I found the problem, and the program itself is a bunch of old spaghetti anyway.

This is just a morsel of a possible clue if anyone else is trying to track down a similar issue in the future.

Graeme.