On Error Skip 1
Goto goto_max_length_label_3456789012
my_return:
Print Choice(Mm.ErrMsg$ = "", "OK", Mm.ErrMsg$)

On Error Skip 1
Goto goto_too_long_label_1234567890123
Print Choice(InStr(Mm.ErrMsg$, "Label too long"), "OK", Mm.ErrMsg$)

On Error Skip 1
Gosub gosub_max_length_label_456789012
Print Choice(Mm.ErrMsg$ = "", "OK", Mm.ErrMsg$)

On Error Skip 1
Gosub gosub_too_long_label_234567890123
Print Choice(InStr(Mm.ErrMsg$, "Label too long"), "OK", Mm.ErrMsg$)

On Error Skip 1
Restore restore_max_length_label_6789012
Print Choice(Mm.ErrMsg$ = "", "OK", Mm.ErrMsg$)

On Error Skip 1
Restore restore_too_long_label_4567890123
Print Choice(InStr(Mm.ErrMsg$, "Variable name too long"), "OK", Mm.ErrMsg$)

End

goto_max_length_label_3456789012:
 goto my_return

gosub_max_length_label_456789012:
 Return

restore_max_length_label_6789012:
 Data 0, 1, 2

> run
OK
OK
OK
OK
OK
OK

> run
Error in line 2: Cannot find label
OK
Error in line 11: Cannot find label
OK
Error in line 19: Cannot find label
OK

Saved 730 bytes
Cannot find label
OK
Cannot find label
OK
Cannot find label
OK

> list
Option Explicit On

On Error Skip
Dim i% = fun_with_max_length_name_6789012%()
? Choice(Mm.ErrMsg$ = "", "OK", "Caught: " + Mm.ErrMsg$)

Function fun_with_max_length_name_6789012%()
 fun_with_max_length_name_6789012% = 42
End Function

> run
Caught: Error in line 7: Variable name too long

const char *skipvar(const char *p, int noerror) {
   const char *pp;
   const char *tp;
   int i;
   int inquote = false;

   tp = p;
   // check the first char for a legal variable name
   skipspace(p);
   if(!isnamestart(*p)) return tp;

   do {
       p++;
   } while(isnamechar(*p));

   // check the terminating char.
   if(*p == '$' || *p == '%' || *p == '!') p++;

   if(p - tp > MAXVARLEN) {
       if(noerror) return p;
       error("Variable name too long");
   }

   pp = p; skipspace(pp); if(*pp == '(') p = pp;
   if(*p == '(') {
       // this is an array <--- also not necessarily true.

       p++;
       if(p - tp > MAXVARLEN) {
           if(noerror) return p;
           error("Variable name too long");
       }