val const : 'a -> 'b -> 'aval o : ('a -> 'b) -> ('c -> 'a) -> 'c -> 'bval filter_map : f:('a -> 'b option) -> 'a list -> 'b listval map_find : f:('a -> 'b option) -> 'a list -> 'b optionval option : 'a -> ('b -> 'a) -> 'b option -> 'aval init_and_last : 'a list -> ('a list * 'a) optionval first_match : 'a list -> 'a list -> 'a option