package travesty

at_most_one xs returns Ok None if xs is empty; Ok Some(x) if it contains only x; and an error otherwise.

Examples:

T_list.at_most_one []     (* ok None *)
       at_most_one [1]    (* ok (Some 1) *)
       at_most_one [1; 2] (* error -- too many *)

one xs returns Ok x if xs contains only x, and an error otherwise.

Examples:

T_list.one []     (* error -- not enough *)
       one [1]    (* ok 1 *)
       one [1; 2] (* error -- too many *)

two xs returns Ok (x, y) if xs is a list containing only x and y in that order, and an error otherwise.

Examples:

T_list.two []        (* error -- not enough *)
       two [1]       (* error -- not enough *)
       two [1; 2]    (* ok (1, 2) *)
       two [1; 2; 3] (* error -- too many *)

max_measure ~measure ~default xs measures each item in xs according to measure, and returns the highest measure reported. If xs is empty, return default if given, and 0 otherwise.

any x ~predicates tests x against predicates until one returns true, in which case it returns true; or all return false, in which case it returns false.

any x ~predicates tests x against predicates until one returns false, in which case it returns false; or all return true, in which case it returns true.

none x ~predicates is the same as any x with all predicates in predicates negated. It tests x against predicates until one returns true, in which case it returns false; or all return false, in which case it returns true.