New range type, distinct from cons cell.

* eval.c (eval_init): Register intrinsic functions rcons,
rangep from and to.
(eval_init): Register rangep intrinsic.

* gc.c (mark_obj): Traverse RNG objects.
(finalize): Handle RNG in switch.

* hash.c (equal_hash, eql_hash): Hashing for for RNG objects.

* lib.c (range_s, rcons_s): New symbol variables.
(code2type): Handle RNG type.
(eql, equal): Equality for ranges.
(less_tab_init): Table extended to cover RNG.
(less): Semantics defined for ranges.
(rcons, rangep, from, to): New functions.
(obj_init): range_s and rcons_s variables initialized.
(obj_print_impl): Produce #R notation for ranges.
(generic_funcall, dwim_set): Recognize range objects for indexing

* lib.h (enum type): New enum member, RNG.  MAXTYPE redefined
to RNG value.
(TYPE_SHIFT): Increased to 5 since there are now 16 type
codes.
(struct range): New struct type.
(union obj): New member rn, of type struct range.
(range_s, rcons_s, rcons, rangep, from, to): Declared.
(range_bind): New macro.

* parser.l (grammar): New rule for recognizing
the #R sequence as HASH_R token.

* parser.y (HASH_R): New terminal symbol.
(range): New nonterminal symbol.
(n_expr): Derives the new range symbol.
The n_expr DOTDOT n_expr rule produces rcons expression rather
than const.

* match.c (format_field): Recognize rcons syntax in fields
which is now what ranges translate to.  Also recognize range
object.

* tests/013/maze.tl (neigh): Fix code which destructures
range as a cons. That can't be done any more.

* txr.1: Document ranges.

1 files changed, 3 insertions, 1 deletions

diff --git a/match.c b/match.c
index 98b35cbc..383cfd80 100644
--- a/match.c
+++ b/match.c
@@ -1353,7 +1353,7 @@ val format_field(val obj, val modifier, val filter, val eval_fun)
     } else if (consp(item) && car(item) == dwim_s) {
       val arg_expr = second(item);
 
-      if (consp(arg_expr) && car(arg_expr) == cons_s) {
+      if (consp(arg_expr) && car(arg_expr) == range_s) {
         val from = funcall1(eval_fun, second(arg_expr));
         val to = funcall1(eval_fun, third(arg_expr));
 
@@ -1362,6 +1362,8 @@ val format_field(val obj, val modifier, val filter, val eval_fun)
          val arg = funcall1(eval_fun, arg_expr);
          if (bignump(arg) || fixnump(arg)) {
            obj = ref(obj, arg);
+         } else if (rangep(arg)) {
+           obj = sub(obj, from(arg), to(arg));
          } else {
            uw_throwf(query_error_s, lit("format_field: bad index: ~s"),
                      arg, nao);