OCaml effects examples

Examples to illustrate the use of algebraic effects in OCaml. See

• Effective Concurrency with Algebraic Effects
• Pearls of Algebraic Effects and Handlers
• Retrofitting Effect Handlers onto OCaml

Examples

• A concurrent round-robin scheduler
• Mutable state
• ML-style refs
• Transactional state
• Asynchronous IO in direct-style
• Dynamic wind
• Deriving generator from any interator
• Promises
• Monadic reflection
• MVars
• Chameneos-redux
• Message-passing pipeline: Sieve of Eratostheneses
• Deep pipes
• Non termination from effects
• Continuation cloning is tricky
• A solution to the Same Fringe Problem
• Reverse-mode Algorithmic Differentiation

The original implementation of Multicore OCaml allowed a user to Obj.clone_continuation. This has been removed, the examples that used this are in the multishot directory. See this conversation about the removal of this feature. They now use the ocaml-multicont library.

• Delimcc encoding
• Nondeterminism
• Backtracking N-Queens
• Memoization
• A mathematical game: Nim

Running the examples

To run the examples with Multicore OCaml, be sure to install Opam with these instructions. If your version of Opam (opam --version) is greater than or equal to 2.1 then the following instructions will work:

# After cloning this repository, create a 5.0.0 switch
opam update
# Add the alpha repository to get unreleased 5.0.0 compatible libraries
opam switch create 5.0.0+trunk --repo=default,alpha=git+https://github.com/kit-ty-kate/opam-alpha-repository.git
opam install . --deps-only

If your version of Opam is less than 2.1, then you will also need to add the beta repository when creating the switch. All of the other commands remain the same.

opam switch create 5.0.0+trunk --repo=default,beta=git+https://github.com/ocaml/ocaml-beta-repository.git,alpha=git+https://github.com/kit-ty-kate/opam-alpha-repository.git

Running make will build all of the examples. If you want to run a single executable that is built with dune you can run:

$ dune exec -- ./<executable_name>.exe

External examples

These are other examples that utilise OCaml effect handlers that are not in this repo:

• Reactive UI and animation
• Probabilisitic Programming
  • and the project report

Citation

If you are citing this work in an academic paper, please cite the PLDI 2021 paper "Retrofitting Effect Handlers onto OCaml": https://dl.acm.org/doi/10.1145/3453483.3454039.