* eval.c (giterate_func, giterate): Adjusting semantics of giterate to

include seed item in the sequence. The while test is applied to
each item before it is passed through the function. Also,
eliminated useless rplacd operation.

* txr.1: Updated documentation of giterate.

1 files changed, 3 insertions, 7 deletions

diff --git a/eval.c b/eval.c
index e44d132f..1c9724cd 100644
--- a/eval.c
+++ b/eval.c
@@ -3160,12 +3160,9 @@ val generate(val while_pred, val gen_fun)
 static val giterate_func(val env, val lcons)
 {
   cons_bind (while_pred, gen_fun, env);
-  val value = lcons->lc.car;
+  val next_item = funcall1(gen_fun, lcons->lc.car);
 
-  if (!funcall1(while_pred, value)) {
-    rplacd(lcons, nil);
-  } else {
-    val next_item = funcall1(gen_fun, value);
+  if (funcall1(while_pred, next_item)) {
     val lcons_next = make_lazy_cons(lcons_fun(lcons));
     rplacd(lcons, lcons_next);
     rplaca(lcons_next, next_item);
@@ -3180,9 +3177,8 @@ static val giterate(val while_pred, val gen_fun, val init_val)
   if (!funcall1(while_pred, init_val)) {
     return nil;
   } else {
-    val first_item = funcall1(gen_fun, init_val);
     val lc = make_lazy_cons(func_f1(cons(while_pred, gen_fun), giterate_func));
-    rplaca(lc, first_item);
+    rplaca(lc, init_val);
     return lc;
   }
 }