index

Lib.index : ('a -> bool) -> 'a list -> int

Finds index of first list element for which predicate holds.

An application index P l returns the index (0-based) to the first element (in a left-to-right scan) of l that P holds of.

Failure

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.

Example

- 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

See also

Lib.el