* parser.y: Allow TXR to support large programs, and efficiently so.

(clauses_rev): New grammar symbol. Uses a left-recursive rule that
does not consume an amount of parser stack proportional to the number
of clauses, and sticks to efficient consing, which means that
the list is built up in reverse.
(clauses): Now just a wrapper rule for clauses_rev which nreverses
its output.
(clauses_opt): Retargetted to use clauses_rev instead of clauses,
and reverse its output.

2 files changed, 19 insertions, 5 deletions

diff --git a/ChangeLog b/ChangeLog
index 2f1e3b68..b26b89f0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,17 @@
 2014-10-18  Kaz Kylheku  <kaz@kylheku.com>
 
+	* parser.y: Allow TXR to support large programs, and efficiently so.
+	(clauses_rev): New grammar symbol. Uses a left-recursive rule that
+	does not consume an amount of parser stack proportional to the number
+	of clauses, and sticks to efficient consing, which means that
+	the list is built up in reverse.
+	(clauses): Now just a wrapper rule for clauses_rev which nreverses
+	its output.
+	(clauses_opt): Retargetted to use clauses_rev instead of clauses,
+	and reverse its output.
+
+2014-10-18  Kaz Kylheku  <kaz@kylheku.com>
+
 	Deal with situation when GC is disabled and the freshobj array runs out
 	of room.  This could happen when parsing a really large TXR program,
 	since gc is disabled during parsing. Currently it asserts, which
diff --git a/parser.y b/parser.y
index 2379602f..6dd79c30 100644
--- a/parser.y
+++ b/parser.y
@@ -97,7 +97,7 @@ int yylex(union YYSTYPE *, yyscan_t scanner);
 
 %token <chr> REGCHAR REGTOKEN LITCHAR SPLICE
 
-%type <val> spec clauses clauses_opt clause
+%type <val> spec clauses_rev clauses clauses_opt clause
 %type <val> all_clause some_clause none_clause maybe_clause block_clause
 %type <val> cases_clause choose_clause gather_clause collect_clause until_last
 %type <val> collect_repeat
@@ -144,11 +144,13 @@ spec : clauses                  { parser->syntax_tree = $1; }
 
      ;
 
-clauses : clause                { $$ = cons($1, nil); }
-        | clause clauses        { $$ = cons($1, $2);  }
-        ;
+clauses : clauses_rev           { $$ = nreverse($1); }
+
+clauses_rev : clause                    { $$ = cons($1, nil); }
+            | clauses_rev clause        { $$ = cons($2, $1);  }
+            ;
 
-clauses_opt : clauses           { $$ = $1; }
+clauses_opt : clauses_rev       { $$ = nreverse($1); }
             | /* empty */       { $$ = nil; }
             ;