$CPU 8086          ' make compatible with XT systems
$LIB ALL OFF       ' turn off all PowerBASIC libraries
$ERROR ALL OFF     ' turn off all PowerBASIC error checking
$OPTIMIZE SIZE     ' optimize for smaller code
 $COMPILE UNIT      ' compile to a UNIT (.PBU)
'$COMPILE EXE       ' compile to a UNIT (.PBU)

DEFINT A-Z         ' Required for all numeric functions, forces PB to not
                   ' include floating point in UNIT (makes it smaller)
'/*------------------------------------------------------------------*/
$CODE SEG "MLIB1"
'/*------------------------------------------------------------------*/
 FUNCTION ISMOUSELBR() PUBLIC AS INTEGER
   REG 1,3
   CALL INTERRUPT &H33
   MButton% = REG(2)
   IF MButton% = 1 THEN
     DELAY .05
     REG 1,3
     CALL INTERRUPT &H33
     MButton% = REG(2)
     IF MButton% = 0 THEN
       FUNCTION = 1
     ELSE
       FUNCTION = 0
     END IF
   END IF

 END FUNCTION
'/*------------------------------------------------------------------*/
'  DO
'    Y$ = INKEY$
'    IF ISMOUSELBR THEN PRINT "YES"
'  LOOP UNTIL Y$ = CHR$(27)