Bifunctors generalise containers whose items contain two pieces of data, and where we can map over both of them at the same time:
type ('a, 'b) t
val bimap : f1:('a -> 'b) -> f2:('c -> 'd) -> ('a, 'c) t -> ('b, 'd) t
This pattern comes up in several places in OCaml/Core:
pairs (t = Tuple2.t);
associative lists (t = List.Assoc.t);
results (t = Result).
It'd be nice if travesty supported this (though I figure the name would be Bi_mappable or something similar). It'd also be nice if travesty supported fixing the type of the first or second item; for example,
type elt
type 'b t (* 'a has become elt *)
val bimap : f1:(elt -> elt) -> f2:('a -> 'b) -> 'a t -> 'b t
and likewise for the other side. (This would be especially helpful for working with Or_error.t—it'd let you combine mapping over results and errors.)
Clown and Joker, which convert a bifunctor to a functor by focusing on the left or right side respectively (though I'd probably not use these names 😁);
Bitraversable, eg generalise Traversable in the same way that Bifunctor generalises Functor;
Maybe explore some of the other things going on in that package.
MattWindsor91
commented
5 years ago
Bifunctors generalise containers whose items contain two pieces of data, and where we can map over both of them at the same time:
This pattern comes up in several places in OCaml/Core:
t = Tuple2.t);t = List.Assoc.t);t = Result).It'd be nice if
travestysupported this (though I figure the name would beBi_mappableor something similar). It'd also be nice iftravestysupported fixing the type of the first or second item; for example,and likewise for the other side. (This would be especially helpful for working with
Or_error.t—it'd let you combine mapping over results and errors.)Another possibility is to implement a few of the ideas from the bifunctors Haskell library:
ClownandJoker, which convert a bifunctor to a functor by focusing on the left or right side respectively (though I'd probably not use these names 😁);Bitraversable, eg generaliseTraversablein the same way thatBifunctorgeneralisesFunctor;