According to Section 13.0 of the FreePascal Language Reference (version 3.2.0)

"A label can be an identifier or an integer digit."

What may be meant is that a label can be an identifier or an integer digit-sequence (and that's what the compiler accepts)

	label := digit-sequence | identifier .

ISO-7185 and ISO-10206 Pascal both define

label = digit-sequence .

UCSD-Pascal defines

label = unsigned-integer ":" .

Turbo Pascal (5.5) defines

label = digit-sequence .

in the range 0..9999

MetroWerks Pascal (unfortunately) defined a label as

label = identifier .

The reason for restricting labels to digit-sequences (excluding identifiers) is a parsing problem:

	a :=3;

can also be read as

a : ......

which is the optional <[ label ":" ]> in the rule for <statement>.

statement = [ label ":" ] [ simple-statement | structured-statement | asm-statement ] .

This can be solved, of course, but misses the elegance of the ISO-7185/ISO-10206/UCSD/Turbo Pascal label definition.

Regards,

Adriaan van Os

Le 17/12/2023 à 17:47, Adriaan van Os via fpc-pascal a écrit :

Turbo Pascal (5.5) defines     label = digit-sequence .

Are you sure ?
I had a doubt and I had a look in some very old source code from 1990 made with tp 5.5, it seems you could have letters in labels.

Excerpt of the code:

PROCEDURE EntCh(var col,lin,lmax:byte;var nbre:boolean;var ch:string);

{entr‚e d'une chaŒne de longueur maxi lmax, si nbre=true, on ne peut entrer}

{que des nombres, signes - et + et point d‚cimal ....                      }

LABEL    e00,e01,e02,e03,e04;
VAR      q,cpos,i,v:byte;
          k           :char;
BEGIN   e00:ch:='';
             q :=0;
             cpos:=col;
             gotoXY(col,lin);
             textbackground(7);textcolor(0);
             for i:=1 to lmax do write('_');
             gotoXY(col,lin);goto e02;
         e01:bip;
         e02:k:=readkey;v:=ord(k);
             if ((q>0) and (v=8)) then

            begin

                  cpos:=cpos-1;q:=q-1;
                  gotoXY(cpos,lin);write('_');
                  ch:=left(ch,length(ch)-1);
                  gotoXY(cpos,lin);
                  goto e02;
             end;
             if ((q=0) and (v=13)) then

            begin

                  ch:=k;goto e04;
             end;
             if (v=13) then goto e04;
             case nbre of
             true : if ((v>47)and (v<58)) or (v=46) then
                    goto e03 else goto e01;
             false: if (v>31) then goto e03 else goto e01;

            end; {case nbre of}

         e03:q:=q+1;if (q>lmax) then goto e01;
             write(k);ch:=ch+k;cpos:=cpos+1;goto e02;
         e04:textbackground(0);textcolor(7);
             gotoXY(col,lin);write(ch);write(space(lmax-length(ch)));

END; {procedure EntCh(...)}

{--------------------------------------------------------------------------}

You are right. I have a printed cope of the Turbo Pascal 6.0 Programmer's Guide and it says, confusingly, on page 16

"The digIt sequence for a label must be in the range 0.9999"

and on page 8

"A label is a digit sequence in the range 0.999".

but on page 9

"As an extension to Standard Pascal, Turbo Pascal also allows identifiers to functions as labels.

Regards,

Adriaan van Os