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
or contact the authors Andrej Bauer Andrej.Bauer@andrej.com and Matija
Pretnar matija@pretnar.info.
Installation & Usage
Prerequisites
We have tested Eff on Mac OS X 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
- OCaml, version 4.02.3 or newer,
- Menhir parser generator, and
- js_of_ocaml OCaml to Javascript compiler.
We do not require, but recommend a command-line editing wrapper such as
rlwrap or
ledit. Eff uses these automatically.
Installing with OPAM
This is the easiest way to install Eff. Follow these steps:
-
Install the OPAM package manager if you do not have it yet.
-
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.
-
Run
opam pin add -k git eff https://github.com/matijapretnar/eff.gitOPAM 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
./configure
If it complains you will have to install missing prerequisites. In case of
problems, make clean distclean might help. The configuration script takes
standard GNU Autoconf arguments, such as --prefix which determines where to
install Eff. Type ./configure --help for more information. Next, run
make
If all goes well, you should be able to run Eff in-place by typing ./eff.
You can also run a battery of tests with
make test
Finally, to install the command eff, run
sudo 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.
Copyright and license
Copyright (c) 2015, Andrej Bauer and Matija Pretnar
Copyright (c) 2012, Timotej Lazar
Eff is distributed under the abbreviated BSD License, see LICENSE.txt for
licensing information.