redirect stdout stdio writeln

[GG]

Hi !
someone could say me if it's possible to redirect stdout of a program running
in background to a file.
I use writeln() to debug, I would like to redirect results of writeln() into
file. I tried :
program >> /tmp/log 2>&1
program >> /tmp/log
program &> /tmp/log
...never success.

so maybe it's not possible with writeln or I'm missing something.

Thanks !