OpenEuphoria

Re: Goto (Was Re: Open Source)

• Posted by Pete Lomax <petelomax at blueyonder.c??uk> Oct 24, 2007
• 826 views

Juergen Luethje wrote:
> 
> This whole discussion is not logical for me. Someone asks for intrducing
> GOTO into Euphoria, and other people make suggestions how to limit the
> damage then.
> The first question should be: Why does someone want GOTO, and exactly
> _for what purposes_? I'm pretty sure then we can find more appropriate
> constructs for the desired purposes -- high level constructs for the
> high level language Euphoria.
> 
Since you ask, I would say to translate a working program written in another
language to Eu. As I recently said, I am not advocating goto, just not standing
against it. Here is one case you probably already saw:

int parse()
{
    Token   tok;

reading:
    tok = gettoken();
    if (tok == END)
        return ACCEPT;
shifting:
    if (shift(tok))
        goto reading;
reducing:
    if (reduce(tok))
        goto shifting;
    return ERROR;
}

And here is that cobol fragment I spoke of last week:

PAGE "Optimised best-fit algorithm"
PROGRAM BEST
DATA DIVISION
77 REQUIRED PIC 9(12) COMP
	VALUE 1659  * Size of G1A
*
77 LIMIT    PIC 9(4) COMP
	VALUE 6     * Length of table
*
01 SIZES
  02 SIZE OCCURS 250	PIC 9(12) COMP
	    VALUE  798
	    VALUE  344
	    VALUE  650
	    VALUE  410
	    VALUE  382
	    VALUE  734
*
01 TS
  02 FILLER PIC 9(4) COMP
	VALUE 6     * Entry length in bytes
  02 TSMAX  PIC 9(4) COMP   * No of entries
  02 FILLER PIC 9(4) COMP   * Work field for sort
  02 FILLER PIC 9(4) COMP
	VALUE 1     * Start of sort key
  02 FILLER PIC 9(4) COMP
	VALUE 6     * Length of sort key
*
01 INCSET
  02 INCLUDE OCCURS 250 PIC X	* 1..250
*
77 LOW-BEST PIC 9(12) COMP
77 LOW-LEVEL	PIC 9(4) COMP
77 LOWSET   PIC X(250)
*
77 HIGH-BEST	PIC 9(12) COMP
77 HIGH-LEVEL	PIC 9(4) COMP
77 HIGHSET  PIC X(250)
*
77 WORK-TOT PIC 9(12) COMP
77 BA-TOT   PIC 9(12) COMP
*
77 LEVEL    PIC 9(4) COMP
77 BA-LEVEL PIC 9(4) COMP
*
77 ITEM     PIC 9(4) COMP
*
01 FILLER REDEFINES ITEM
  02 FILLER PIC X
  02 ITB2   PIC X	* 1..250
*
77 BA-ITEM  PIC 9(4) COMP
*
01 FILLER REDEFINES BA-ITEM
  02 FILLER PIC X
  02 BA-ITB2	PIC X	    * 1..250
*
77 INDEX    PIC 9(4) COMP
77 BA-IDX   PIC 9(4) COMP
*
PROCEDURE DIVISION
    MOVE LIMIT TO TSMAX
    CALL TSRT$ USING TS SIZES          -- a sort()
    PERFORM DA-FIND-COMBINATION
    ON NO EXCEPTION                    -- eg "EXIT 1" gives exception;
	DO                             --  (In Eu just use a flag)
	MOVE WORK-TOT TO BA-TOT
	MOVE LEVEL TO BA-LEVEL
	PERFORM BA-DISPLAY
	PERFORM DA200
	ON EXCEPTION FINISH
	ENDDO
    END
    MOVE LOWSET TO INCSET
    MOVE LOW-LEVEL TO BA-LEVEL
    MOVE LOW-BEST TO BA-TOT
    DISPLAY "Lower figure"
    PERFORM BA-DISPLAY
    MOVE HIGHSET TO INCSET
    MOVE HIGH-LEVEL TO BA-LEVEL
    MOVE HIGH-BEST TO BA-TOT
    DISPLAY "Higher figure"
    PERFORM BA-DISPLAY
EXIT
 
SECTION BA-DISPLAY
    DISPLAY BA-TOT
    DO FOR BA-IDX = 1 TO BA-LEVEL
	MOVE 0 TO BA-ITEM
	MOVE INCLUDE(BA-IDX) TO BA-ITB2       -- uses () for subscripts!
	DISPLAY BA-ITEM
	DISPLAY "  " SAMELINE
	DISPLAY SIZE(BA-ITEM) SAMELINE
    ENDDO
    DISPLAY "       Key <CR>"
    SVC 6 USING 1                   -- wait_key()
    ON EXCEPTION
    END
EXIT
 
SECTION DA-FIND-COMBINATION
*
* This section tries to find a set of sizes which add up to the
* required amount exactly.
*
    MOVE 1 TO LEVEL
    MOVE 0 TO LOW-BEST
    MOVE 999999999 TO HIGH-BEST
    MOVE LIMIT TO ITEM
DA100.
    MOVE ITB2 TO INCLUDE(LEVEL)
*
* Add size(item) to work-tot
*
    $LOAD SIZE(ITEM)     -- you can follow this, I trust. acc = size[item].
    $ADDS WORK-TOT                               --  work_tot+=acc
    $SUB REQUIRED                    -- acc = size[item]+work_tot-required
    $EXIT EQ		* Found exact fit
    $JUMP GT DA200	    * Too big
*
* This set is smaller than required - save it if it is best so far
*
    IF WORK-TOT > LOW-BEST
	$ADDS LOW-BEST
	MOVE LEVEL TO LOW-LEVEL
	MOVE INCSET TO LOWSET
    END
    IF ITEM > 1 	* More to be tested
	$STORE ITEM
	ADD 1 TO LEVEL	    * Leave item in table;
	GOTO DA100
DA200.
*
* This set is larger than required - save it if it is best so far
*
	IF WORK-TOT < HIGH-BEST
	$ADDS HIGH-BEST
	MOVE LEVEL TO HIGH-LEVEL
	MOVE INCSET TO HIGHSET
	END
    END
DA300.
*
* Now we need to backtrack;  remove item from running total and look
* at the next instead.
*
* Subtract size(item) from work-tot
*
    $LOAD 0
    $SUB SIZE(ITEM)
    $ADDS WORK-TOT
    IF ITEM > 1 	* More to be tested
	$STORE ITEM	* Look at next (overwrite item in table)
	GOTO DA100
    END
*
* We have exhausted all possibilities at this level; backtrack to
* a previous level.
*
    MOVE #00 TO INCLUDE(LEVEL)
    ADD -1 TO LEVEL
    $EXIT EQ 1		* All done
    MOVE 0 TO ITEM
    MOVE INCLUDE(LEVEL) TO ITB2
    GOTO DA300
 
ENDPROG

I found it quite a challenge to get that working in Eu.

Regards,
Pete