Hi, I am trying to sent to a variable to tcl/tk and unify there it with a string. I wrote the prolog code: :- use_module(library(tcltk)). :- use_package(classic). go(A):- tk_new([name('Simple')], Tcl), tcl_eval(Tcl, 'source simple2.tcl', _), tcl_eval(Tcl, ['ask', br(write(A))], _), tk_main_loop(Tcl), tcl_delete(Tcl). and the tcl file simple2.tcl proc ask {var} { unify_term $var my_value } unfortunatelly when I query for go(S). the interpeter goes into a loop (!?). Where I am wrong. Are there any example code somewhere in the world? Thanks Massimo