       10 // ABS() sample program
       20 //
       30 FOR f:=-1 TO 1 STEP 0.01 DO
       40   IF f<0 THEN
       50     g:=-f
       60   ELSE
       70     g:=f
       80   ENDIF
       90   SYS assert, ABS(f)=g
      100 ENDFOR f
      110 PRINT "Ok"
