tfausak

Invertible syntax descriptions

An "invertible syntax description" is something that can be used to both parse and generate a syntax. For example, instead of defining separate toJson and fromJson functions for a given data type, an invertible syntax description could be used to provide both. There are many Haskell libraries that provide this functionality or something close to it. As far as I can tell most of them are at least inspired by Invertible syntax descriptions by Tillmann Rendel and Klaus Ostermann.

Personally I am interested in using these for HTTP routing. I frequently want to be able to define a route such as /episodes/:id.json, dispatch based on that route, and generate links to that route. Doing so manually is tedious and error prone.

tfausak

-- This whole thing is shamelessly stolen from:
-- <https://doisinkidney.com/snippets/nary-uncurry.html>.

-- Without flexible instances, GHC complains about the `HasApply` instances:
--
-- > Illegal instance declaration for `HasApply a Z`. All instance types must
-- > be of the form `(T a1 ... an)` where `a1 ... an` are *distinct type
-- > variables*, and each type variable appears at most once in the instance
-- > head.
--