- list-index pred clist_1 clist_2 ...procedure
Return the index of the leftmost element that satisfies PRED.
If there are N list arguments CLIST_1 ... CLIST_N, then PRED must be a function taking N arguments and returning a boolean result.
list-index applies PRED to the first elements of the CLIST_I parameters. If this application returns true, list-index immediately returns zero. Otherwise, it iterates, applying PRED to the second elements of the CLIST_I parameters, then the third, and so forth. When it finds a tuple of list elements that cause PRED to return true, it stops and returns the zero-based index of that position in the lists.
The iteration stops when one of the lists runs out of values; in this case, list-index returns #f.
(list-index even? '(3 1 4 1 5 9)) => 2 (list-index < '(3 1 4 1 5 9 2 5 6) '(2 7 1 8 2)) => 1 (list-index = '(3 1 4 1 5 9 2 5 6) '(2 7 1 8 2)) => #f