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

SYNOPSIS
Finds index of first list element for which predicate holds.

KEYWORDS
searching.

DESCRIBE
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




SEEALSO
Lib.el.

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