seq iterators: new peek operation.

* lib.c (seq_iter_peek_nil, seq_iter_peek_list,
seq_iter_peek_vec, seq_iter_peek_hash): New static functions.
(seq_geti): New function.
(seq_iter_init): Initialize new peek member of seq_iter
structure.

* lib.h (struct seq_iter): New member, peek.
(seq_peek): New inline function.
(seq_geti): Declared.

1 files changed, 39 insertions, 0 deletions

diff --git a/lib.c b/lib.c
index 1794fa99..d9c23678 100644
--- a/lib.c
+++ b/lib.c
@@ -311,6 +311,11 @@ static int seq_iter_get_nil(seq_iter_t *it, val *pval)
   return 0;
 }
 
+static int seq_iter_peek_nil(seq_iter_t *it, val *pval)
+{
+  return 0;
+}
+
 static int seq_iter_get_list(seq_iter_t *it, val *pval)
 {
   if (!it->ui.iter)
@@ -320,6 +325,14 @@ static int seq_iter_get_list(seq_iter_t *it, val *pval)
   return 1;
 }
 
+static int seq_iter_peek_list(seq_iter_t *it, val *pval)
+{
+  if (!it->ui.iter)
+    return 0;
+  *pval = car(it->ui.iter);
+  return 1;
+}
+
 static int seq_iter_get_vec(seq_iter_t *it, val *pval)
 {
   if (it->ui.index < it->ul.len) {
@@ -329,12 +342,34 @@ static int seq_iter_get_vec(seq_iter_t *it, val *pval)
   return 0;
 }
 
+static int seq_iter_peek_vec(seq_iter_t *it, val *pval)
+{
+  if (it->ui.index < it->ul.len) {
+    *pval = ref(it->inf.obj, num(it->ui.index));
+    return 1;
+  }
+  return 0;
+}
+
 static int seq_iter_get_hash(seq_iter_t *it, val *pval)
 {
   *pval = hash_next(it->ui.iter);
   return *pval != nil;
 }
 
+static int seq_iter_peek_hash(seq_iter_t *it, val *pval)
+{
+  *pval = hash_peek(it->ui.iter);
+  return *pval != nil;
+}
+
+val seq_geti(seq_iter_t *it)
+{
+  val v = nil;
+  (void) it->get(it, &v);
+  return v;
+}
+
 void seq_iter_rewind(val self, seq_iter_t *it)
 {
   switch (it->inf.kind) {
@@ -364,21 +399,25 @@ void seq_iter_init(val self, seq_iter_t *it, val obj)
     it->ui.iter = nil;
     it->ul.len = 0;
     it->get = seq_iter_get_nil;
+    it->peek = seq_iter_peek_nil;
     break;
   case SEQ_LISTLIKE:
     it->ui.iter = it->inf.obj;
     it->ul.len = 0;
     it->get = seq_iter_get_list;
+    it->peek = seq_iter_peek_list;
     break;
   case SEQ_VECLIKE:
     it->ui.index = 0;
     it->ul.len = c_num(length(it->inf.obj));
     it->get = seq_iter_get_vec;
+    it->peek = seq_iter_peek_vec;
     break;
   case SEQ_HASHLIKE:
     it->ui.iter = hash_begin(it->inf.obj);
     it->ul.len = 0;
     it->get = seq_iter_get_hash;
+    it->peek = seq_iter_peek_hash;
     break;
   default:
     unsup_obj(self, obj);