FoldWhile¶

Folds a function over a list while a predicate holds, returning the first accumulator value for which the predicate fails (or the final value if it never fails).

$ wo 'FoldWhile[Times, 2, {2, 3, 4, 5}, # < 100 &]'
240

The initial value is tested first, so a value that already fails is returned without any folding:

$ wo 'FoldWhile[Times, 2, {2, 3, 4, 5}, # < 1 &]'
2

The three-argument form takes the initial value from the head of the list:

$ wo 'FoldWhile[Plus, {1, 2, 3, 4, 5}, # < 6 &]'
6

An m argument supplies the last m results to the test:

$ wo 'FoldWhile[Times, 1, {2, 2, 3, 3, 4}, Unequal, 2]'
144

A trailing n continues folding n extra times past the failing value (or steps back with a negative value):

$ wo 'FoldWhile[Plus, 0, {1, 2, 3, 4, 5}, # < 6 &, 1, 1]'
10