Egison is the pattern-matching-oriented, purely functional programming language. We can directly represent pattern-matching against lists, multisets, sets, trees, graphs and any kind of data types. This is the repository of the interpreter of Egison.
For more information, visit Egison website. You can try Egison online!
If you get interested in Egison, please contact Satoshi Egi or tweet to @Egison_Lang.
At first, you should install Haskell Platform.
After you installed Haskell Platform, run the following commands on the terminal.
% cabal update
% cabal install egison
Now, you can try Egison.
% egison
Egison Version X.X.X(C) 2011-2014 Satoshi Egi
http://www.egison.org
Welcome to Egison Interpreter!
> ^D
Leaving Egison Interpreter.
If you are a beginner of Egison, it would be better to install egison-tutorial.
% cabal update
% cabal install egison-tutorial
% egison-tutorial
Egison Tutorial for Version X.X.X (C) 2013-2014 Satoshi Egi
http://www.egison.org
Welcome to Egison Tutorial!
==============================
List of sections in the tutorial
1: Calculate numbers
2: Basics of functional programming
3: Define your own functions
4: Basic of pattern-matching
5: Pattern-matching against infinite collections
6: Writing scripts in Egison
==============================
Choose a section to learn.
(1-6): 5
====================
We can write a pattern-matching against infinite lists even if that has infinite results.
Note that Egison really enumerates all pairs of two natural numbers in the following example.
Examples:
(take 10 (match-all nats (set integer) [<cons $m <cons $n _>> [m n]]))
====================
>
We can try it also online. Enjoy!
We can do non-linear pattern-matching against unfree data types in Egison. An unfree data type is a data type whose data have no canonical form, a standard way to represent that object. It enables us to write more elegant programs.
We can use pattern-matching for enumeration. The following code enumerates all twin primes from the infinite list of prime numbers with pattern-matching!
(define $twin-primes
(match-all primes (list integer)
[<join _ <cons $p <cons ,(+ p 2) _>>>
[p (+ p 2)]]))
;; Enumerate first 10 twin primes
(take 10 twin-primes)
;=>{[3 5] [5 7] [11 13] [17 19] [29 31] [41 43] [59 61] [71 73] [101 103] [107 109]}
The following code is the program that determines poker-hands written in Egison. All hands are expressed in a single pattern.
(define $poker-hands
(lambda [$cs]
(match cs (multiset card)
{[<cons <card $s $n>
<cons <card ,s ,(- n 1)>
<cons <card ,s ,(- n 2)>
<cons <card ,s ,(- n 3)>
<cons <card ,s ,(- n 4)>
<nil>>>>>>
<Straight-Flush>]
[<cons <card _ $n>
<cons <card _ ,n>
<cons <card _ ,n>
<cons <card _ ,n>
<cons _
<nil>>>>>>
<Four-of-Kind>]
[<cons <card _ $m>
<cons <card _ ,m>
<cons <card _ ,m>
<cons <card _ $n>
<cons <card _ ,n>
<nil>>>>>>
<Full-House>]
[<cons <card $s _>
<cons <card ,s _>
<cons <card ,s _>
<cons <card ,s _>
<cons <card ,s _>
<nil>>>>>>
<Flush>]
[<cons <card _ $n>
<cons <card _ ,(- n 1)>
<cons <card _ ,(- n 2)>
<cons <card _ ,(- n 3)>
<cons <card _ ,(- n 4)>
<nil>>>>>>
<Straight>]
[<cons <card _ $n>
<cons <card _ ,n>
<cons <card _ ,n>
<cons _
<cons _
<nil>>>>>>
<Three-of-Kind>]
[<cons <card _ $m>
<cons <card _ ,m>
<cons <card _ $n>
<cons <card _ ,n>
<cons _
<nil>>>>>>
<Two-Pair>]
[<cons <card _ $n>
<cons <card _ ,n>
<cons _
<cons _
<cons _
<nil>>>>>>
<One-Pair>]
[<cons _
<cons _
<cons _
<cons _
<cons _
<nil>>>>>>
<Nothing>]})))
(poker-hands {<Card <Club> 12>
<Card <Club> 10>
<Card <Club> 13>
<Card <Club> 1>
<Card <Club> 11>});=><Straight-Flush>
(poker-hands {<Card <Diamond> 1>
<Card <Club> 2>
<Card <Club> 1>
<Card <Heart> 1>
<Card <Diamond> 2>});=><Full-House>
(poker-hands {<Card <Diamond> 4>
<Card <Club> 2>
<Card <Club> 5>
<Card <Heart> 1>
<Card <Diamond> 3>});=><Straight>
(poker-hands {<Card <Diamond> 4>
<Card <Club> 10>
<Card <Club> 5>
<Card <Heart> 1>
<Card <Diamond> 3>});=><Nothing>
Isn't it exciting? The pattern-matching of Egison is very powerful. We can use it for pattern-matching against graphs or tree-structures such as XML. Egison is not famous at all now. Please help us to make Egison popular.
There are a lot of existing work for pattern-matching.
The advantage of Egison is that it realized all of the following features at the same time.
- Modularization of the way of pattern-matching for each data type
- Pattern-matching with multiple results (backtracking)
- Non-linear pattern-matching
It enables us to express non-linear pattern-matching against unfree data types intuitively as above demonstrations.
Furthermore, Egison realized the following feature. We can even modularize patterns like functions keeping above features.
- Non-linear pattern-matching with lexical scoping
The Pattern-Matching Mechanism section in Egison developer's manual explains how we realized that.
Please read our paper on arXiv.org for details.
% cabal install --enable-tests
% cabal test
% sudo apt-get install haskell-platform-doc haskell-platform-prof
% cabal install --enable-library-profiling --enable-executable-profiling
% egison +RTS -p -RTS -l sample/sequence.egi
% cat egison.prof
I thank Ryo Tanaka, Takahisa Watanabe, Takuya Kuwahara and Kentaro Honda for their help to implement the interpreter.
Copyright (c) 2011-2014, Satoshi Egi
Egison is released under the MIT license.
I used husk-scheme by Justin Ethier as reference to implement the base part of the previous version of the interpreter.
Egison is sponsored by Rakuten, Inc. and Rakuten Institute of Technology.