todo: update

[Akim Demaille]

commit 8426663631cd16f9d344ddb5e72468a9cb7344c7
Author: Akim Demaille <address@hidden>
Date:   Tue Dec 31 07:29:11 2019 +0100

    todo: update

diff --git a/TODO b/TODO
index 7a3580cc..c955c951 100644
--- a/TODO
+++ b/TODO
@@ -1,4 +1,8 @@
 * Bison 3.6
+** Consistency
+YYUNDEFTOK is an internal symbol number, as YYTERROR.
+But YYERRCODE is an external token number.
+
 ** doc
 I feel its ugly to use the GNU style to declare functions in the doc.  It
 generates tons of white space in the page, and may contribute to bad page
@@ -50,6 +54,15 @@ syntax error, unexpected $end, expecting ↦ or 🎅🐃 or '\n'
 While at it, we should stop using "$end" by default, in favor of "end of
 file", or "end of input", whatever.  See how lalr1.java does that.
 
+** Better error messages
+The users are not provided with enough tools to forge their error messages.
+See for instance "Is there an option to change the message produced by
+YYERROR_VERBOSE?" by Simon Sobisch, on bison-help.
+
+See also
+https://www.cs.tufts.edu/~nr/cs257/archive/clinton-jefferey/lr-error-messages.pdf
+and https://research.swtch.com/yyerror.
+
 ** consistency
 token vs terminal, variable vs non terminal.
 
@@ -436,6 +449,11 @@ An Experimental Ambiguity Detection Tool ∗ Sylvain Schmitz
 LORIA, INRIA Nancy - Grand Est, Nancy, France
 
 * Extensions
+** More languages?
+Well, only if there is really some demand for it.
+
+https://github.com/scfc/bison-php/blob/master/data/lalr1.php
+
 ** Multiple start symbols
 Would be very useful when parsing closely related languages.  The idea is to
 declare several start symbols, for instance
@@ -458,15 +476,6 @@ happen with yy_start: stmt | expr).  Then adjust the 
skeletons so that this
 initial token (YY_START_STMT, YY_START_EXPR) be shifted first in the
 corresponding parse function.
 
-** Better error messages
-The users are not provided with enough tools to forge their error messages.
-See for instance "Is there an option to change the message produced by
-YYERROR_VERBOSE?" by Simon Sobisch, on bison-help.
-
-See also
-https://www.cs.tufts.edu/~nr/cs257/archive/clinton-jefferey/lr-error-messages.pdf
-and https://research.swtch.com/yyerror.
-
 ** %include
 This is a popular demand.  We already made many changes in the parser that
 should make this reasonably easy to implement.