Convert each-family operators to use iter-begin.

With this change we can do (each ((x vec)) ...) with
reasonable efficiency, because we are no longer marching
through the vector with cdr, copying the suffix.

* eval.c (get_iter_f): New global variable.
(op_each): Obtain iterators for all the objects with
iter_begin, instead of treating them as lists. Probe the
iterators for termination with iter_more, get the items with
iter_item instead of car and step with iter_step instead of
cdr.
(eval_init): gc-protect the get_iter_f function and initialize
it.

* share/txr/stdlib/compiler.tl (expand-each): Replace the
car/cdr and null testing with iter-init, iter-more, iter-item
and iter-step.

1 files changed, 5 insertions, 4 deletions

diff --git a/share/txr/stdlib/compiler.tl b/share/txr/stdlib/compiler.tl
index 3b5caffe..36e33007 100644
--- a/share/txr/stdlib/compiler.tl
+++ b/share/txr/stdlib/compiler.tl
@@ -1385,12 +1385,13 @@
            (out (if (member each-type '(collect-each append-each))
                   (gensym)))
            (accum (if out (gensym))))
-      ^(let* (,*(zip gens vars) ,*(if accum ^((,out (cons nil nil)) (,accum ,out))))
+      ^(let* (,*(mapcar (ret ^(,@1 (iter-begin ,@2))) gens vars)
+               ,*(if accum ^((,out (cons nil nil)) (,accum ,out))))
          (block nil
            (sys:for-op ()
-                       ((and ,*gens) ,*(if accum ^((cdr ,out))))
-                       (,*(mapcar (ret ^(sys:setq ,@1 (cdr ,@1))) gens))
-             ,*(mapcar (ret ^(sys:setq ,@1 (car ,@2))) vars gens)
+                       ((and ,*(mapcar (op list 'iter-more) gens)) ,*(if accum ^((cdr ,out))))
+                       (,*(mapcar (ret ^(sys:setq ,@1 (iter-step ,@1))) gens))
+             ,*(mapcar (ret ^(sys:setq ,@1 (iter-item ,@2))) vars gens)
              ,*(caseq each-type
                  (collect-each ^((rplacd ,accum (cons (progn ,*body) nil))
                                  (sys:setq ,accum (cdr ,accum))))