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https://github.com/matijapretnar/eff

A functional programming language based on algebraic effect handlers
https://github.com/matijapretnar/eff

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A functional programming language based on algebraic effect handlers

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README 

        
# Eff



Eff is a functional programming language based on algebraic effects and

their handlers.



Algebraic effects are a way of adding computational effects to a pure

functional setting. In a technical sense they are subsumed by the monadic

approach to computational effects, but they offer new ways of programming

that are not easily achieved with monads. In particular, algebraic effects

are combined seamlessly, whereas monad transformers are needed in the

monadic style.



The main idea of Eff is that computational effects are accessed through a

set of operations, for example `lookup` and `update` for state, `read` and

`write` for I/O, `raise` for exceptions, etc. The behavior of operations is

determined by handlers. Just like an exception handler determines what

happens when an exception is raised, a general handler describes the

actions taken when an operation is triggered. Examples of handlers include

state, transactions, non-determinism, stream redirection, backtracking,

delimited continuations, and many others.



Because Eff supports first-class effects and handlers, programmers may

define new computational effects, combine existing ones, and handle effects

in novel ways. For instance, ML-style references are a defined concept in

Eff.



Eff code looks and feels like that of OCaml because Eff uses OCaml syntax

extended with constructs for effects and handlers. Furthermore, Eff is a

statically typed language with parametric polymorphism and type inference.

The types are similar to those of OCaml and other variants of ML in the

sense that they do not express any information about computational effects.



For further information visit the [Eff page](http://www.eff-lang.org/)

or contact the authors Andrej Bauer  and

Matija Pretnar .



## Installation & Usage



### Prerequisites



We have tested Eff on macOS and Linux, and it should work on other

Unix-like systems. In principle, nothing prevents Eff from running

on Windows, we just have not tested it yet.



To install Eff, you need a standard Unix-style build environment as well as



1. [OCaml](https://ocaml.org/), version 4.14.1 or newer,

2. [Js_of_ocaml](http://ocsigen.github.io/js_of_ocaml) compiler from OCaml bytecode to Javascript

3. its syntax extension `js_of_ocaml-ppx`,

4. [Menhir](http://gitlab.inria.fr/fpottier/menhir) LR(1) parser generator,

5. [OCamlFormat](https://github.com/ocaml-ppx/ocamlformat) auto-formatter for OCaml code.



We do not require, but recommend a command-line editing wrapper such as

[rlwrap](http://freecode.com/projects/rlwrap) or

[ledit](http://cristal.inria.fr/~ddr/ledit/). Eff uses these automatically.



### Installing with OPAM



This is the easiest way to install Eff. Follow these steps:



1. Install the [OPAM package manager](http://opam.ocamlpro.com) if you do not have it yet.



2. Make sure you have the correct OCaml compiler activated. Since Eff compiles with all recent version of OCaml you probably need not worry about this step.



3. Run



        opam pin add -k git eff https://github.com/matijapretnar/eff.git



   OPAM will download and build the necessary dependencies first, then download

   and build Eff itself.



### Manual installation



To compile Eff manually, first clone the GitHub repository



    git clone https://github.com/matijapretnar/eff.git

    cd eff



and run



    make



If all goes well, you should be able to run Eff in-place by typing `./eff.exe`.



You can also run a battery of tests with



    make test



Finally, to install the command `eff`, run



    make install



See the file `etc/README.txt` for editor support.



### Using Eff



There are examples of Eff in `examples` subdirectory that should get you started. The Eff

syntax is very close to that of OCaml. You can find further material about Eff on the [Eff page](http://www.eff-lang.org/).



## License



Eff is distributed under the abbreviated BSD License, see `LICENSE.txt` for

licensing information.