Itertools

Lazy iterators over lists, following the spirit of Python's itertools. Both live on the ABS_ITERATOR type.

#include "abscom/abs.h"

Function	Description
var chain(var list_a, var list_b)	Yield every element of a, then every element of b.
var cycle(var list)	Yield a list's elements forever, wrapping at the end.
var repeat(var val, int n)	Yield val exactly n times, then None forever.
var iter_next(var iter)	The next element, or None once the iterator is exhausted.

var a = List();
append(a, v(1)); append(a, v(2));
var b = List();
append(b, v(10)); append(b, v(20));

var c = chain(a, b);
print(iter_next(c));   /* 1  */
print(iter_next(c));   /* 2  */
print(iter_next(c));   /* 10 */
print(iter_next(c));   /* 20 */
print(iter_next(c));   /* None (stays None afterwards) */

var cy = cycle(a);
print(iter_next(cy));   /* 1 */
print(iter_next(cy));   /* 2 */
print(iter_next(cy));   /* 1 */
print(iter_next(cy));   /* 2 */

var r = repeat(v("beep"), 3);
print(iter_next(r));   /* beep */
print(iter_next(r));   /* beep */
print(iter_next(r));   /* beep */
print(iter_next(r));   /* None */

Notes:

• chain treats a non-list source as empty, so chain(a, None) just drains a. cycle on an empty or non-list source yields None forever.
• repeat with n <= 0 yields nothing. The repeated value is emitted as-is, so repeat(None, 3) is indistinguishable from an exhausted iterator.
• iter_next on a non-iterator returns ABS_ERROR.

See tests/test_itertools.c for the full test.