Change Lens type from Tuple to a record/union

[LAJW]

A great package, I'm enjoying it thoroughly, with the exception of compile errors.

It quite often happens the type checker substitutes the type alias for the actual type (espcially in the case of an inferred type and especially in the case of an error) and produces errors more difficult to parse than they would be if the lens was stored not as a tuple but rather a record:

expected: Lens<MyRecord, int>
vs
expected: (MyRecord -> int) * (int -> MyRecord -> MyRecord)

Which needless to say gets worse with the complication of either of the types involved.

Would this be something you'd be willing to consider changing or is it too compatibility breaking to be worth thinking about?

[varon]

Lenses are defined as tuples to allow for libraries to implement them without a dependency on aether.

It also means that different lens libraries can interop.

To get clean types, create an alias for Lens<'a, 'b> = ('a -> b) * ('b -> 'a -> 'a) and a simple helper function:

let lens get set: Lens<_,_> = (get,set)

[LAJW]

@varon and I do that (using Aether's Lens alias). The problem with aliases though is they too often get expanded in erroneous situations.

[varon]

It may also depend on your tooling, but there's not all that much you can do aside from specifying signatures.

[LAJW]

One thing that could be done is making Aether work with a record type. I rolled my own subset of lense methods and errors were consistently better, but I thought it would be nice if it was integrated into the library.

Unless not having to include aether to use lenses is a valuable enough of a feature...

[stijnmoreels]

To get clean types, create an alias for Lens<'a, 'b> = ('a -> b) * ('b -> 'a -> 'a) and a simple helper function:

let lens get set: Lens<_,_> = (get,set)

Can we maybe consider including these helper functions in the library? Especially when dealing with complex lenses, it can get confused if your tuple has the right kind of types.

These ones, could already save us a lot of trouble:

module Lens =
  let create getter setter : Lens<'a, 'b> = getter, setter
module Prism =
  let create getter setter : Prism<'a, 'b> = getter, setter
module Isomorphism =
  let create left right : Isomorphism<'a, 'b> = left, right
module Epimorphism =
  let create left right : Epimorphism<'a, 'b> = left, right

Happy to contribute.