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https://github.com/memowe/perlisp

A simple Lisp interpreter, written in Perl
https://github.com/memowe/perlisp

currying interpreter lisp-interpreter perl repl

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A simple Lisp interpreter, written in Perl

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README 

        
# PerLisp [![Build Status](https://travis-ci.org/memowe/perlisp.svg?branch=master)](https://travis-ci.org/memowe/perlisp)



This is a simple statically scoped Lisp interpreter, written in Perl. During the

lecture "Structure and Interpretation of Programming Languages", held by Achim

Clausing (WWU Münster, Germany), I needed to try out different things, so I

wrote this.



**DISCLAIMER** This is **not** production ready. I use it to play around and I

think there are many bugs lurking around. You have been warned! :-)



How to start?

-------------



Install PerLisp like a normal Perl distro:



    $ perl Makefile.PL

    $ make

    $ make test

    $ make install

    $ make clean



Now you can call the perlisp script which starts a read eval print loop (see

more details below):



    $ perlisp



If you want to hack PerLisp, view the API docs via



    $ perldoc PerLisp



If you don't want to install all that stuff, you can call the `perlisp` script

from the project root directory:



    $ cd ~/code/perlisp

    $ perl perlisp



And it should just work. Now let's do some Lisp stuff!



PerLisp uses the `bind` operator to bind values to names, you have a `lambda`

operator to create function values and the convenience operator `define` to bind

a function to a name in one step. With the `bound` operator you get a list of

all bound names. Most of them come from the `init.perlisp` file, which is loaded

while the interpreter starts.



Start typing something like this:



> `(+ 17 25)`  

> **42**  

> `(define (square x) (* x x))`  

> **Function: (x) -> (* x x)**  

> `(square 42)`  

> **1764**



You can find more inspirations from `PerLisp::Init` and the tests, especially

`t/50-init.t`, which shows some use cases for the init functions.



### Some interesting stuff



* Like Haskell, PerLisp fully supports **autocurryfication**, which means a

function applied to too few arguments will return a function with parameters

for the remaining arguments automagically. It's super-easy to define useful

functions using autocurryfication in combination with some well known higher

order functions:



> `(bind product (reduce * 1))`  

> **Function: (l) -> (cond (nil? l) 1 (* (car l) (reduce * 1 (cdr l))))**  

> `(product (list 2 7 3))`  

> **42**



* PerLisp is able to interpret a simple Lisp interpreter written in Lisp which

is able to run itself inside PerLisp. Amazing! And there's a test for it in

`t/61-lisplisp.t`. However, to calculate even a simple expression in a

three-level nested interpreter chain takes some time so you have to enable the

test explicitly by setting the `LISPLISP` environment variable to a true value.



Interpreter details

-------------------



The implementation is straight forward. PerLisp uses objects from the following

classes to get you started with Lisp:



* `PerLisp::Lexer` - generates a `PerLisp::TokenStream` from Lisp strings

* `PerLisp::Parser` - generates `PerLixp::Expr::*` objects from a TokenStream

* `PerLisp::Expr::*` - Lisp expressions

* `PerLisp::Context` - objects which store value-name bindings

* `PerLisp::Operators` - perl implementations of built-in operators

* `PerLisp::Init` - a container package around the init script



View the code for more implementation details, I tried hard to make it very

readable (even if you don't know much Perl).



Author, bug reports, license

----------------------------



Copyright (c) Mirko Westermeier, 



This software is released under the MIT license (view MIT-LICENSE for details).



If you found a bug, please contact me via mail or github. You can also use

github's issue tracker. Please provide (failing) tests for your bugs, patches or

feature requests.