! @ pr:x_getfilename.graphic VARIABLE_NAME [ passed_name ] [filter]
! note that the filter is a filter without the leading asterism ('*')
! since we use the ampersand ('&') substitution system
gui\panel  "Choose a File" x_getfilename.graphic
on error quit
let &1 &2 /prompt "File ?" /file "*&3"
gui\go
! Trick to wait and kill the panel after completion
gui\wait
gui\panel toto toto
gui\go