todo: d: push and token ctors are done

[Akim Demaille]

commit b7d2b854be147053103b277c586cbdc35ad896ac
Author: Akim Demaille <akim.demaille@gmail.com>
Date:   Wed Aug 4 21:42:04 2021 +0200

    todo: d: push and token ctors are done

diff --git a/TODO b/TODO
index 2e66eeec5..2eab70979 100644
--- a/TODO
+++ b/TODO
@@ -304,102 +304,6 @@ maintenance *simple* by avoiding any gratuitous 
difference.
 ** CI
 Check when gdc and ldc.
 
-** Token Constructors
-It is possible to mix incorrectly kinds and values, and for instance:
-
-        return parser.Symbol (TokenKind.NUM, "Hello, World!\n");
-
-attaches a string value to NUM kind (wrong, of course).  When
-api.token.constructor is set, in C++, Bison generated "token constructors":
-parser.make_NUM. parser.make_PLUS, parser.make_STRING, etc.  The previous
-example becomes
-
-        return parser.make_NUM ("Hello, World!\n");
-
-which would easily be caught by the type checker.
-
-** Push Parser
-Add support for push parser.  Do not start a nice skeleton, just enhance the
-current one to support push parsers.  This is going to be a tougher nut to
-crack.
-
-First, you need to understand well how the push parser is expected to work.
-To this end:
-- read the doc
-- look at examples/c/pushcalc
-- create an example of a Java push parser.
-- have a look at the generated parser in Java, which has the advantage of
-  being already based on a parser object, instead of just a function.
-
-The C case is harder to read, but it may help too.  Keep in mind that
-because there's no object to maintain state, the C push parser uses some
-struct (yypstate) to preserve this state.  We don't need this in D, the
-parser object will suffice.
-
-I think working directly on the skeleton to add push-parser support is not
-the simplest path.  I suggest that you (1) transform a generated parser into
-a push parser by hand, and then (2) transform lalr1.d to generate such a
-parser.
-
-Use `git commit` frequently to make sure you keep track of your progress.
-
-*** (1.a) Prepare pull parser by hand
-Copy again one of the D examples into say examples/d/pushcalc.  Also
-check-in the generated parser to facilitate experimentation.
-
-- find local variables of yyparse should become members of the parser object
-  (so that we preserve state from one call to the next).
-
-- do it in your generated D parser.  We don't need an equivalent for
-  yypstate, because we already have it: that the parser object itself.
-
-- have your *pull*-parser (i.e., the good old yy::parser::parse()) work
-  properly this way.  Write and run tests.  That's one of the reasons I
-  suggest using examples/d/calc as a starting point: it already has tests,
-  you can/should add more.
-
-At this point you have a pull-parser which you prepared to turn into a
-push-parser.
-
-*** (1.b) Turn pull parser into push parser by hand
-
-- look again at how push parsers are implemented in Java/C to see what needs
-  to change in yyparse so that the control is inverted: parse() will
-  be *given* the tokens, instead of having to call yylex itself.  When I say
-  "look at C", I think your best option are (i) yacc.c (look for b4_push_if)
-  and (ii) examples/c/pushcalc.
-
-- rename parse() as push_parse(Symbol yyla) (or push_parse(TokenKind, Value,
-  Location)) that takes the symbol as argument.  That's the push parser we
-  are looking for.
-
-- define a new parse() function which has the same signature as the usual
-  pull-parser, that repeatedly calls the push_parse function.  Something
-  like this:
-
-int parse ()
-{
- int status = 0;
- do {
-  status = this->push_parse (yylex());
- } while (status == YYPUSH_MORE);
- return status;
-}
-
-- show me that parser, so that we can validate the approach.
-
-*** (2) Port that into the skeleton
-- once we agree on the API of the push parser, implement it into lalr1.d.
-  You will probaby need help on this regard, but imitation, again, should
-  help.
-
-- have example/d/pushcalc work properly and pass tests
-
-- add tests in the "real" test suite.  Do that in tests/calc.at.  I can
-  help.
-
-- document
-
 ** GLR Parser
 This is very ambitious.  That's the final boss.  There are currently no
 "clean" implementation to get inspiration from.