[Chicken-users] FFI with callbacks for gnu readline

[Levi Pearson]

I'm writing a command-line app that I would like to have a readline  
interface to, complete with custom tab-completion.  The readline.egg  
package doesn't do tab-completion, so I've been working on my own,  
but I've run into some problems.

The readline library expects to be able to call a generator function  
with a string and an index and get back a newly-allocated string that  
it can use and then free().  To accommodate this, I wrote a C  
function that calls a define-external'd scheme function that returns  
a scheme-object containing the string.  I found that returning a c- 
string would sometimes give me some garbage characters as the strings  
were not always null-terminated at the right spot.  The C function  
gets the string length and c-string pointer out of the scheme-object,  
makes a newly-allocated copy, and passes it back to readline.

This all seems to work well, but after a bit of use of the tab- 
completion functionality, the program segfaults or otherwise dies on  
a call to the readline interface.  I've packaged up a pretty minimal  
test case, which can be downloaded from http://lifeoflevi.com/ 
crasher.tar.gz

I'd appreciate any help I can get, as this problem has been haunting  
me for a couple of days now.

                --Levi