'{$STAMP BS2pe}
'{$PBASIC 2.5}
' (c) 2003 Tracy Allen, http://www.emesystems.com
' explores the PBASIC 2.5 commands 
'   DO - EXIT - LOOP
' and
'   FOR - EXIT - NEXT
' 
' to use this program as a study guide,
' Enter alternative program cases after #DEFINE below
' then look at tokens using CTRL-M memory map window
' (Scroll to the bottom of the window to the red area).


#DEFINE example=10
'  10  DO - EXIT - LOOP in new PBASIC
'  11  same exact tokens as 10 using IF, GOTOs and labels in old PBASIC
'  12  simplified form of 10, with no statements before EXIT
'  13  same tokens as 12, using IF GOTOs and labels in old PBASIC
'  14  same as 13, but optimized (saves 2 GOTOs, 42 bits)

'  20  FOR - EXIT - NEXT in new PBASIC
'  21  same exact tokens as 20 using IF, GOTOs and labels in old PBASIC
'  22  same as 21 but optimized (saves 42 bits)
'  23  a more complicated situation, with statements preceding EXIT
'  24  same as 23, using IF GOTOs and labels in old PBASIC



#SELECT EXAMPLE


' ------ DO - EXIT - LOOP
#CASE 10
  DO
    ' statements A
    IF IN1 THEN statements B : EXIT
    ' statements C
  LOOP
  ' statements D, after loop exits
  END



#CASE 11  ' same tokens as case 10
lab1a:
  ' statements A
  IF IN1 THEN lab1b
  GOTO lab1c
lab1b:
  ' statements B
   GOTO lab1d    ' this is the EXIT
lab1c:
 ' statements C
  GOTO lab1a
lab1d:
  ' statements D, after loop exits
  END
  


#CASE 12   ' simplified form of 10, with no statements B before the EXIT
  DO
    ' statements A
    IF IN1 THEN EXIT    ' simple EXIT stands alone
    ' statements C
  LOOP
  ' statements D, after loop exits
  END



#CASE 13  ' same tokens as case 12, IF-THEN fully parsed
lab1a:
' statements A
  IF IN1 THEN lab1b
  GOTO lab1c
lab1b:       ' this is the EXIT part, only a goto
  GOTO lab1d
lab1c:
  ' statements C
  GOTO lab1a
lab1d:
  ' statements D, after loop exits
  END
  

#CASE 14  ' optimized version of 14, saves two GOTOs
lab1a:
  ' statements A
  IF IN1 THEN lab1d   ' exits directly
  ' statements C
  goto lab1a:
lab1d:
  ' statements D execute after loop exits
    END





' ------ FOR - EXIT - NEXT
#CASE 20
  FOR x=1 to 15
    ' statements A
    IF in1 THEN statements B : EXIT
    ' statements C
  NEXT
  ' statements D execute after loop exits
  END


#CASE 21  ' same tokens as case 20
lab1:
  FOR x=1 to 15
    ' statements A
    IF IN1 THEN lab1b
    GOTO lab1c
lab1b:
    ' statements B
    GOTO lab1d
lab1c:
    ' statements C
  NEXT
lab1d:
  ' statements D exectute after loop exits
  END
  

#CASE 22  ' simplified version of 20, without statements B
  FOR x=1 to 15
    ' statements A
    IF in1 THEN EXIT
    ' statements C
  NEXT
  ' statements D execute after loop exits
  END


#CASE 23  ' same tokens as case 20
lab1:
  FOR x=1 to 15
    ' statements A
    IF IN1 THEN lab1b
    GOTO lab1c
lab1b:
    GOTO lab1d
lab1c:
    ' statements C
  NEXT
lab1d:
  ' statements D exectute after loop exits
  END


#CASE 24  ' same effect as 23, but more efficient
          ' short circuits two GOTOs.  Saves 42 bits.
lab1a:
  ' statements A
  IF IN1 THEN lab1d     ' directly out of loop if no statements preceed the EXIT
  ' statements B
  GOTO lab1a
lab1d:
  ' statements D exectute after loop exits
  END
  
 

#ENDSELECT