Add functions for upgrading isomorphisms to work with producers

[torgeirsh]

No description provided.

[Gabriella439]

I have a couple of suggestions:

• Use Lens' instead of Iso'. Unfortunately, using the more general Iso' doesn't gain you anything because the isomorphism functions from lens (like from) are hard-coded to the Exchange type exported from the lens library.
• Maybe simplify the API to:

mapIso :: (a -> b) -> (b -> a) -> Lens' (Producer a m x) (Producer b m x)

[torgeirsh]

The simpler API doesn't allow users to transform pure lenses into "piped"
ones directly, but on the ather hand requiring users to call 'withIso' from
'lens' themselves neatly sidesteps the need for 'Exchange' in
'pipes-parse'. Are 'lens-family' users out of luck though?

2014-06-13 1:22 GMT+02:00 Gabriel Gonzalez notifications@github.com:

I have a couple of suggestions:

Use Lens' instead of Iso'. Unfortunately, using the more general Iso'
doesn't gain you anything because the isomorphism functions from lens
(like from) are hard-coded to the Exchange type exported from the lens
library.

Maybe simplify the API to:

mapIso :: (a -> b) -> (b -> a) -> Lens' (Producer a m x) (Producer b m x)

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#30 (comment)
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[Gabriella439]

lens-family users are indeed out of luck no matter what you do, since lens-family doesn't support a way to represent isomorphisms. This would require lens-family to depend on profunctors, but one of the design principles behind lens-family is to only depend on packages in the Haskell Platform.

However, like you said, lens users can still use the simpler mapIso if they just call withIso. I would really like to avoid reimplementing Exchange inside of pipes-parse, because I would also like pipes-parse to depend solely on the Haskell Platform.