New function: rangeref.

Because ranges can be iterated like sequences, and are
identified as vector-like, they have to support indexing.
However, ranges already have semantics as a function:
with a sequence argument, they slice it.

Let's put the semantics into a function called rangeref,
so it can be coherently documented.

* eval.c (eval_init): Register rangeref intrinsic.

* lib.c (generic_funcall): Range as a function works in
terms of rangeref.
(ref): Handle RNG case via rangeref.
(rangeref): New function.

* lib.h (rangeref): Declared.

* tests/012/seq.tl: New tests.

1 files changed, 34 insertions, 1 deletions

diff --git a/lib.c b/lib.c
index 7875c7d2..97a36e3e 100644
--- a/lib.c
+++ b/lib.c
@@ -8537,7 +8537,7 @@ INLINE val do_generic_funcall(val fun, varg args_in)
     case 0:
       callerror(fun, lit("missing required arguments"));
     case 1:
-      return sub(args->arg[0], fun->rn.from, fun->rn.to);
+      return rangeref(fun, args->arg[0]);
     default:
       callerror(fun, lit("too many arguments"));
     }
@@ -13288,6 +13288,8 @@ val ref(val seq, val ind)
     return vecref(seq, ind);
   case BUF:
     return buf_get_uchar(seq, ind);
+  case RNG:
+    return rangeref(seq, ind);
   default:
     type_mismatch(lit("ref: ~s is not a sequence"), seq, nao);
   }
@@ -14039,6 +14041,37 @@ val in_range_star(val range, val num)
   }
 }
 
+val rangeref(val range, val ind)
+{
+  val self = lit("rangeref");
+
+  if (integerp(ind))
+  {
+    val fr = range->rn.from;
+    val to = range->rn.to;
+    val eind = ind;
+
+    if (to != t && to != colon_k) {
+      val len = minus(to, fr);
+
+      if (minusp(eind))
+        eind = plus(eind, len);
+
+      if (minusp(eind) || ge(eind, len))
+        goto err;
+    } else if (minusp(eind)) {
+      goto err;
+    }
+
+    return plus(fr, eind);
+  err:
+    uw_throwf(error_s, lit("~a: ~s is out of range for ~s"),
+              self, ind, range, nao);
+  }
+
+  return sub(ind, range->rn.from, range->rn.to);
+}
+
 #if CONFIG_LOCALE_TOLERANCE
 
 static void locale_init(void)