たとえばこんな感じ

THREAD bglog
print 1
DIM ret = SLCTBOX(...)
print ret
bContinue = FALSE


FUNCTION bglog
 LOGPRINT( TRUE, 0, G_SCREEN_H-100)
  WHILE 1
   IFB (FALSE = bContinue) THEN
    BREAK
   ENDIF
  WEND
 RESULT=0
FEND