index : ('a -> bool) -> 'a list -> int
Synopsis: Finds index of first list element for which predicate holds.
Keywords: searching.
index P l
returns the index (0-based) to the first
element (in a left-to-right scan) of l
that P
holds of. If P
doesn't hold of any element of l
, then index P l
fails. If P x
fails for any x
encountered in the scan, then index P l
fails.
- index (equal 3) [1,2,3]; > val it = 2 : int - let fun even i = (i mod 2 = 0) in try (index even) [1,3,5,7,9] end; Exception raised at Lib.index: no such element ! Uncaught exception: ! HOL_ERR - index (equal 3 o hd) [[1],[],[2,3]]; ! Uncaught exception: ! Empty
Lib
, el
.