[Rd] Feature Request: Allow Underscore Separated Numbers

[Duncan Murdoch]

On 16/07/2022 5:24 a.m., Ivan Krylov wrote:
> On Fri, 15 Jul 2022 12:34:24 -0700
> Bill Dunlap <williamwdunlap using gmail.com> wrote:
> 
>> The token '._1' (period underscore digit) is currently parsed as a
>> symbol (name).  It would become a number if underscore were ignored
>> as in the first proposal.  The just-between-digits alternative would
>> avoid this change.
> 
> Thanks for spotting this! Here's a patch that allows underscores
> only between digits and only inside the significand of a number:

I think there's an issue with hex values.  For example:

 > 0xa_2
[1] 162
 > 0x2_a
Error: unexpected input in "0x2_"

So "a" counts as a digit in 0xa_2, but not as a digit in 0x2_a.

Duncan Murdoch


> 
> --- src/main/gram.y	(revision 82598)
> +++ src/main/gram.y	(working copy)
> @@ -2526,7 +2526,7 @@
>       YYTEXT_PUSH(c, yyp);
>       /* We don't care about other than ASCII digits */
>       while (isdigit(c = xxgetc()) || c == '.' || c == 'e' || c == 'E'
> -	   || c == 'x' || c == 'X' || c == 'L')
> +	   || c == 'x' || c == 'X' || c == 'L' || c == '_')
>       {
>   	count++;
>   	if (c == 'L') /* must be at the end.  Won't allow 1Le3 (at present). */
> @@ -2538,11 +2538,16 @@
>   	    if (count > 2 || last != '0') break;  /* 0x must be first */
>   	    YYTEXT_PUSH(c, yyp);
>   	    while(isdigit(c = xxgetc()) || ('a' <= c && c <= 'f') ||
> -		  ('A' <= c && c <= 'F') || c == '.') {
> +		  ('A' <= c && c <= 'F') || c == '.' || c == '_') {
>   		if (c == '.') {
>   		    if (seendot) return ERROR;
>   		    seendot = 1;
>   		}
> +		if (c == '_') {
> +		    /* disallow underscores following 0x or followed by non-digit */
> +		    if (nd == 0 || typeofnext() >= 2) break;
> +		    continue;
> +		}
>   		YYTEXT_PUSH(c, yyp);
>   		nd++;
>   	    }
> @@ -2588,6 +2593,11 @@
>   		break;
>   	    seendot = 1;
>   	}
> +	/* underscores in significand followed by a digit must be skipped */
> +	if (c == '_') {
> +	    if (seenexp || typeofnext() >= 2) break;
> +	    continue;
> +	}
>   	YYTEXT_PUSH(c, yyp);
>   	last = c;
>       }
> 
>