Is there an `id` of `prism' id Just`?-CodePudding

I have a function called:

mapRouteEncoder ::
  Prism' FilePath FilePath ->
  Prism' r1 r2 ->
  (b -> a) ->
  RouteEncoder a r1 ->
  RouteEncoder b r2

This function is often used by specifying "identity" prisms (if we can call it that) in the first two arguments because only the 3rd function is specified, viz.:

    stringRouteEncoder
      & mapRouteEncoder (prism' id Just) (prism' id Just) changeModel

I use optics-core, and is there anything in that library to replace prism' id Just something more idiomatic?

CodePudding user response：

I'm not familiar with the idioms for that package, but I'd be tempted to use castOptic equality to turn the identity Iso into a Prism. That seems to get the idea across pretty well. However, I would expect that in most contexts you wouldn't actually need to convert it to a Prism; you can presumably use polymorphic functions (like preview and review) that will accept an Iso as well as a Prism.

In your case, I suspect the right approach would be to write something like

mapRouteEncoder ::
  ( p1 `Is` A_Prism
  , p2 `Is` A_Prism) =>
  Optic' p1 ixy1 FilePath FilePath ->
  Optic' p2 ixy2 r1 r2 ->
  (b -> a) ->
  RouteEncoder a r1 ->
  RouteEncoder b r2