Extensible effects. Minimal boilerplate. (Weakened inference).

See Vinyl.Effects.Example for a detailed tutorial.

Dependencies:

• the free package, for Free (which transforms a functor into a monad) and Cofree (which transforms a functor into a comonad).
• the vinyl package, for (TODO) CoRec (an n-ary, un-nested sum type) and Rec (an n-ary, un-nested product type).

Concepts (necessary only for contributing to the library, not using it):

• for composing domain-specific languages and interpeters (parts 1 to 5):

  • http://dlaing.org/cofun/posts/free_and_cofree.html
  • http://dlaing.org/cofun/posts/monad_transformers_and_comonad_transformers.html
  • http://dlaing.org/cofun/posts/coproducts_for_free_and_products_for_cofree.html
  • http://dlaing.org/cofun/posts/pairing_and_io.html
  • http://dlaing.org/cofun/posts/pairing_over_the_network.html
  • (this series a tour-de-force, read it!).

• for "extensible records":

  • https://hackage.haskell.org/package/vinyl-0.5.2/docs/Data-Vinyl-Tutorial-Overview.html

• for "free monads":

  • <> TODO tekmos blog

• for "extensible effects":

  • <> TODO ocharles

• for mtl:

  • <> TODO

Reverse Dependencies:

• packdeps.haskellers.comreversevinyl-effects
• TODO workflow-types uses this package to maximize the effects the platform-independent monad provides, while still preserving the richer effects the platform-specific monads provide (in workflow-linux, workflow-osx, and workflow-windows). e.g. OSX can easily access the clipboard via bash.

Extensions:

• The effects as a type-level set, not a type-level list (from GHC.TypeLits); i.e. the items are unique. (Currently, I think the duplicates are ignored).
• "extensible interpreters" via cofree comonads. (The original motivation for this package only needed the Language to be extensible).

Existing Alternatives:

• effects: uses -XOverloadedInstances. bad inference?
• <> romansch:
• <> ocharles:
• <> mtl: doesn't compose