[Rd] Feature Request: Allow Underscore Separated Numbers

[Ivan Krylov]

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:

--- 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;
     }


-- 
Best regards,
Ivan