This is a Haskell library which explores some ideas around continuations and co-exponentials.

The library has the following modules:

• Control.Monad.Coexp: a monadic interface for coexponentials
• Control.Monad.Control: a monadic interface for control operators using coexponentials
• Data.Coexp: implementation of coexponential types using Cont
• Data.Coexp.Backtrack: backtracking combinators
• Control.Monad.Free.Control: codensity encoding of Free monads using coexponentials
• Control.Arrow.Coapply: coarrows
• Data.Profunctor.Coclosed: coclosed profunctors

The examples are implemented in the following modules.

• Examples.SAT.Guess: bruteforce SAT solver using continuations
• Examples.SAT.Backtrack: backtracking SAT solver using the coexponential combinators
• Examples.Eff.Toss: Sam Lindley's drunken toss example of effect handlers encoded using codensity
• Examples.TS.Backtrack: backtracking tree search using the coexponential combinators

There is a test suite which:

• benchmarks the brute-force SAT solver against the backtracking SAT solver, and
• runs some test cases on the drunken toss example,
• tests the tree search example.

$ cabal build all
$ cabal run coexp-test -- --quickcheck-tests 1000

Any contributions and suggestions are most welcome.

Here are some other repositories (that I know of), which also explore continuations and co-exponentials:

• https://github.com/mstewartgallus/prologish/
• https://github.com/fresnel/fresnel
• https://github.com/robrix/sequoia
• https://github.com/jmanuel1/idris-stuff/