|Syntax||LOCal var1 *[, varx [(index1 *[indexi]* )] ]*|
This command must only be used as the first executable line within either a PROCedure or FuNction definition block (ie. it can only be preceded by REMark lines) - if it is used elsewhere, it will cause a ‘bad line’ error when the program is RUN. Under SMS’s improved interpreter the error ‘Misplaced LOCal’ will be reported.
LOCal must be followed by a list of variables which are said to be ‘local’ to that definition block. This means that although a variable may already have been used within the main body of the program, if it is local to that definition block, on entry its value is stored and it is then made ‘unset’ (without value), and can then be used for any means within that definition block (or within any sub-procedure or sub-function called by that definition block).
When the definition block is left (with END DEFine or RETurn), the variable is restored to its original value.
Arrays can also be made LOCal by placing an index after their name, which is used to specify their size (as with DIM). Indeed this is the only way in which a simple variable can also be used as an array. In any event, the parameters contained in the definition line are local to that definition block and can also be safely used in the main program - these are in fact swapped with the actual parameters passed for the duration of the definition block (see DEFine PROCedure).
This program shows the status of three variables at various stages - note how x can be used as an array in the main program and a simple variable within the PROCedure definition block:
100 DIM x(10) 110 test$='Wait' 120 moder=4:x(1)=10 130 PRINT moder,test$,x(1) 140 Change_vars 150 PRINT moder,test$,x(1) 155 : 160 DEFine PROCedure Change_vars 170 LOCal moder(2,10),x,test$ 180 PRINT moder(1,5),test$,x 190 test$='Changed':moder(1,5)=10 200 x=5 210 PRINT moder(1,5),test$,x 220 END DEFine
This produces the following output:
4 Wait 10 line 130 0 * * line 180, local variables 10 Changed 5 line 210, local variables 4 Wait 10 line 150
On pre MG ROMs, any more than nine parameters may corrupt the program, by replacing names with PRINT towards the end of a program. This can however be circumvented by increasing the size of the Name Table by 8 bytes for each name (plus a little more for luck), by using the line:
This bug is fixed on the ST/QL Emulator (with E-Init software v1.27+), Minerva and SMS.
On most ROMs, you cannot LOCal the names of the parameters passed to the PROCedure or FuNction. ROMs which can cope with this will simply set the passed value to undefined. Type in the following small procedure test:
100 DEFine PROCedure test(a,b) 110 LOCal a 120 PRINT a,b 130 END DEFine
If your interpreter behaves correctly then:
SMS will print:
Any reference to a in the procedure, eg. a=a+1, will break with an error in expression (-17) because the LOCal declaration of a undefined the passed parameter. You would need to expressly assign a value to a within the PROCedure for this to work. This works correctly on Minerva ROMs (ie. a is unset by the LOCal command).