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
• Dynamic State

Running the examples

To run the examples with OCaml, be sure to install Opam with these instructions.

# After cloning this repository, create a 5.1 switch
opam update
opam switch create 5.1.1
opam install . --deps-only

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.