New function: iterp.

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

* lib.[ch] (iterp): New function.

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

* txr.1: Document iterp. Update documentation for iter-more,
iter-item and iter-step to more precisely identify which
objects are valid arguments in terms of iterp and additional
conditions, and that other objects throw a type-error
exception. Fix wrong references to iter-more under
documentation for iter-item.  Removed obsolete text specifying
that iter-step uses car on list-like sequences, a dubious
behavior removed in the previous commit.

1 files changed, 22 insertions, 0 deletions

diff --git a/lib.c b/lib.c
index 1e127e88..cf137699 100644
--- a/lib.c
+++ b/lib.c
@@ -1440,6 +1440,28 @@ val iter_reset(val iter, val obj)
   }
 }
 
+val iterp(val obj)
+{
+  switch (type(obj)) {
+  case NIL:
+  case CHR:
+  case NUM:
+  case BGNUM:
+  case FLNUM:
+  case CONS:
+  case LCONS:
+    return t;
+  case COBJ:
+    if (obj->co.cls == seq_iter_cls)
+      return t;
+    if (obj_struct_p(obj) && get_special_slot(obj, iter_step_m))
+      return t;
+    /* fallthrough */
+  default:
+    return nil;
+  }
+}
+
 val iter_catv(varg iters)
 {
   cnum index = 0;