# Module `List.Or_unequal_lengths`

`Or_unequal_lengths`

is used for functions that take multiple lists and that only make sense if all the lists have the same length, e.g., `iter2`

, `map3`

. Such functions check the list lengths prior to doing anything else, and return `Unequal_lengths`

if not all the lists have the same length.

`val compare : ('a -> 'a -> int) -> 'a t -> 'a t -> int`

`val sexp_of_t : ('a -> Base.Sexp.t) -> 'a t -> Base.Sexp.t`