Topic       : The GFA-Basic Compendium
Author      : GFA Systemtechnik GmbH
Version     : GFABasic.HYP v2.98 (12/31/2023)
Subject     : Documentation/Programming
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Index Size  : 28056
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View Ref-FileGOTO label

label: label name

By means of a 'label', specific locations in the program can be defined and a
program started from this point with the instruction 'GOTO label'. Program
execution is commenced from the label position. The label can consist of
letters, numbers, underlines, and periods. However, unlike variable names, it
may also begin with a number. It must, however, end with a colon. The colon
should be left off when refering to a label in a GOTO command.

The use of GOTO is not allowed for jumping out of procedures, functions, or
FOR-NEXT loops into the main part of the program. The use of this command also
leads to unclear program structures which are not easy to follow and, it is
generally considered, GOTO's should be avoided wherever possible.

Example:

    PRINT "place 1"
    GOTO jump_point
    PRINT "place 2"
    jump_point:
    PRINT "place 3"

--> The texts "place 1" and "place 3" appear on the screen.

Memo: If the label used with GOTO is undefined the compiler will not
      issue an error message. Instead the compiler writes a bad binary where
      GOTO is translated into JMP 0.l!

This example shows what is and what is not valid when using the GOTO command:
FOR j=0 TO 31
  IF i=15
    ' GOTO label3   !no good
  ENDIF
NEXT j
FOR i=0 TO 31
  IF i=15
    ' GOTO main1    !no good
    GOTO label3     !ok       jump within the same loop
  ENDIF
label3:
NEXT i
' GOTO label1       !no good
' GOTO label2       !no good
' GOTO label3       !no good
main1:
'
PROCEDURE proc1
  GOTO label1       !ok       jump into another procedure from a procedure
  ' GOTO label2     !no good
  ' GOTO main1      !no good
RETURN
PROCEDURE proc2
  GOTO label1       !ok       jump within the same procedure
label1:
RETURN
FUNCTION func1
  GOTO label2       !ok       jump into another function from a function
  ' GOTO label1     !no good
  ' GOTO main1      !no good
  RETURN 0
ENDFUNC
FUNCTION func2
  GOTO label2       !ok       jump within the same function
label2:
  RETURN 0
ENDFUNC