json: implement distinguished json quasiquote.

Because #J<json> produces the (json ...) form that translates
into quote, ^#J<json> yields a quasiquote around a quote. This
has some disadvantages, because it requires an explicit eval
in some situtions to do what the programmer wants.

Here, we introduce an alternative: the syntax #J^<json> will
produce a quasiquote instead of a quote.

The new translation scheme is

  #J X  -> (json quote <X>)

  #J^ X -> (json sys:qquote <X>)

where <X> denotes the Lisp object translation of JSON syntax X.

* parser.c (me_json): The quote symbol is now already in the
json form, so all that is left to do here is to take the cdr
to pop off the json symbol.

* parser.l (JPUNC, NJPUNC): Allow ^ to be a punctuator in
JSON mode.

* parser.y (json): For regular #J, generate the new (json
quote ...) syntax. Implement J# ^ which sets up the nonzero
quasi_level around the processing of the JSON syntax, so that
everything is in a quasiquote, finally producing the
(json sys:qquote ...) syntax.

* lex.yy.c.shipped, y.tab.c.shipped: Updated.

1 files changed, 4 insertions, 2 deletions

diff --git a/parser.y b/parser.y
index ddd78bd1..21064a9f 100644
--- a/parser.y
+++ b/parser.y
@@ -938,9 +938,11 @@ tree : HASH_T list             { if (parser->quasi_level > 0 && unquotes_occur($
                                  yybadtok(yychar, lit("tree node literal")); }
      ;
 
-json : HASH_J json_val          { $$ = cons(json_s, cons($2, nil));
+json : HASH_J json_val          { $$ = list(json_s, quote_s, $2, nao);
                                   end_of_json(scnr); }
-
+     | HASH_J '^'               { parser->quasi_level++; }
+       json_val                 { parser->quasi_level--;
+                                  $$ = list(json_s, sys_qquote_s, $4, nao); }
 json_val : NUMBER               { $$ = $1; }
          | JSKW                 { $$ = $1; }
          | '"' '"'              { $$ = null_string; }