Eden - lua-based scripting language in clojure

eden is a language akin to traditional scripting languages like lua, python or ruby. It is embeddable, extensible, sandboxed, and familiarly simple.

eden is unique, in that it uses only valid EDN data values for data representation. This has the added benefit of ridiculously easy clojure interoperability.

eden is still in beta development, so things are going to be broken, undocumented, and error messages are close to non-existent.

(require '[eden.core :as eden])

(eden/eval println("Hello World!"))
;; Hello World!
;;

(eden/eval
 local x = 2 + 2

 function add2(x)
   return x + 2
 end

 println("The value of x plus 2 equals" add2(x)))
;; The value of x plus 2 equals 6
;;

Almost all of clojures core libraries work out-of-the-box within eden

(eden/eval println(rest([1 2 3 4]))) ;; (2 3 4)

(eden/eval println(conj([1 2 3] 4))) ;; [1 2 3 4]

(eden/eval
 local x = list(1 2 3 4)
 for i in x do
   println(i)
 end)
 ;; 1
 ;; 2
 ;; 3
 ;; 4

Even higher-level clojure functions work in eden

(eden/eval
 local result = map(inc vector(1 2 3 4))
 println(result))
;; (2 3 4 5)

(eden/eval
 local sum = reduce(function(a b) return a + b end list(1 2 3 4))
 println(sum))
;; 10

Functions written in eden can be used within clojure

(eden/eval
 function addfirst2(xs)
   return first(xs) + second(xs)
 end)

(def addfirst2 (eden/get-var 'addfirst2))
(println (addfirst2 [1 2 3 4]))
;; 3

Functions written in clojure can be used within eden

(defn hello [name]
  (str "Hello " name "!"))

(eden/set-var! 'hello hello)
(eden/eval hello("Ben")) ;; "Hello Ben!"

eden uses dot notation for retrieving and assigning to EDN collections, like vectors and hash maps.

(eden/eval
 local person = {}
 person.first-name = "John"
 person.last-name = "Doe"
 person.age = 12
 println(person))
;; {:first-name John, :last-name Doe, :age 12}

;;
;; similarly, vectors can be accessed using square bracket notation
;;

(eden/eval
 local list-of-letters = ["a" "b" "c"]
 println(list-of-letters[1])) ;; b

The getter syntax makes it much easier to manipulate more complex collections.

(eden/eval
 local default-person = {}
 default-person.first-name = "John"
 default-person.last-name = "Doe"

 local display = function(p)
   println(p.first-name "-" p.last-name)
 end

 local person-list = [
   default-person
   default-person
 ]

 person-list[0].first-name = "Ben"
 person-list[0].last-name = "Z"
 person-list[1].first-name = "Jane"
 person-list[1].last-name "M"

 println(person-list)
 display(person-list[0]))
 ;; [{:first-name Ben, :last-name Z} {:first-name Jane, :last-name Doe}]
 ;; Ben - Z

1 Rationale

eden was developed to be a embedded language within a natively compiled clojure application (GraalVM’a native-image). It can be used to expose the application API so that a userbase can create plugins in a sandboxed environment. The applications of eden within clojure are very similar to the applications of lua within c/c++.

eden can also be used as a standalone scripting language. A natively compiled commandline tool has been developed, and can be used to manipulate EDN files similar to how you would implement JSON files in javascript. Everything is still in its early stages, so I would not recommend using it in a production setting.

I also plan on compiling eden to clojurescript, although the applications of eden within clojurescript are not of interest to me at the moment.

2 Requirements

eden requires clojure 1.9+

3 Installation

3.1 Native Executable

Native Executables can be found on the releases page

There are currently native executables generated for debian-based linux systems, and for rpm-based systems.

If you would like to generate your own native executable, please follow the configuration instructions included in the Makefile.

An example use:

$ eden -e "println(\"Hello World!\")"
Hello World!
$

;; hello.eden

function hello(name)
  return str("Hello " name "!")
end

local name = system.args[0] or "there"
println(hello(name))

$ eden hello.eden ben
Hello ben!

3.2 Uberjar

Alternatively, the uberjar can be found on the releases page, which can be run as follows with java

java -jar eden-<version>-standalone.jar <filename>

3.3 Clojure Installation

For the latest version, please visit clojars.org

Leiningen/Boot

[eden "0.9.0"]

Clojure CLI/deps.edn

eden {:mvn/version "0.9.0"}

Gradle

compile 'eden:eden:0.9.0'

Maven

<dependency>
  <groupId>eden</groupId>
  <artifactId>eden</artifactId>
  <version>0.9.0</version>
</dependency>

3.4 Docker Image Execution

If you wish to just try out eden, and you have docker installed, give this a shot:

$ docker run --rm -ti benzap/eden:0.8.0-1 -e '"Hello Eden!"'

Using eden with docker has its issues, as you have to mount volumes in order to execute scripts. Here is a small example, which mounts my current working directory under the volume /mount, so that it can execute an eden script that also resides in my current working directory.

$ docker run --rm -v `pwd`:/mount -ti benzap/eden:0.8.0-1 /mount/my_script.eden

4 Introduction

eden is an imperative language, so it embraces the idea of mutable values being passed around. However, eden re-uses the persistent data collections that make up clojure, which makes eden copy-on-write when performing operations on collections.

function people-eq?(p1 p2)
  if p1 == p2 then
    println("Are Equal!")
  else
    println("Not Equal!")
  end
end

local person1 = {:first-name 12 :age 12}
local person2 = person1

people-eq?(person1 person2) ;; Are Equal!

person2.age = 13

people-eq?(person1 person2) ;; Not Equal!

In a more traditional language like lua, person2 would hold a reference to the same data structure as person1. However, eden uses copy-on-write semantics. They never share a reference. If you want to share a reference between variables, use a clojure atom.

local person1 = atom({:first-name "Ben" :age 12})
local person2 = person1
              
swap!(person2 function(p) p.age = 13 return p end)
println(deref(person1)) ;; {:first-name Ben, :age 13}

5 Installing the Eden Console for Administrative Tooling

eden can be run from the commandline, which can make it suitable for commandline scripting. It can evaluate expressions with the -e commandline flag, or can evaluate files, which are usually designated with the suffix *.eden.

The easiest way to try out eden is to clone the project and run it within the project directory.

$ git clone https://github.com/benzap/eden.git
$ cd eden
$ lein run ./examples/eden/get_project_version.eden
0.8.0

5.1 Debian Installation

Tested in Ubuntu 17.10, 18.10.

May require stdc++ lib dependencies for other distributions.

wget https://github.com/benzap/eden/releases/download/0.8.0/eden-0.8.0-amd64.deb
sudo dpkg -i eden-0.8.0-amd64.deb

5.2 Redhat Installaion

Tested on Fedora 28

wget https://github.com/benzap/eden/releases/download/0.8.0/eden-0.8.0-1.x86_64.rpm
sudo rpm -i eden-0.8.0-1.x86_64.rpm

5.3 Running the standalone uberjar

Grab a pre-generated uberjar from the releases page, and run it directly:

$ java -jar eden-0.8.0-standalone.jar ./examples/eden/basic_http_server.eden

The best use of eden as a standalone tool is to either build your own native executable, or grab one of the pre-compiled ones provided on the releases page

5.4 Installing on Windows

experimental

Download the *.exe from the releases page

Note: Has issues with the current working directory, *.jar recommended

6 Programming in Eden

This is a short manual explaining the Eden programming language.

6.1 Values and Types

Eden is a dynamically typed language based on data types provided in the EDN data format. The types include:

Integers / BigIntegers

0, 13, -13, 14N

Floats / Doubles

3.14, 10e+3

Strings

~”Hello”~

Keywords

:foo, :bar

Booleans

true, false

Symbols (vars)

x, y

Lists

list(1 2 3), list(4 5 6)

Vectors

[1 2 3], vector(1 2 3)

Maps

{:a 123 :b 456}

Set

#{:a :b :c}, set(:a :b :c)

Nil

nil

I encourage you to review the EDN data format for additional types you might experience when using Eden.

6.2 Variables

Variables in Eden are presented in the form of Symbols. The extent of allowed variable names consists of what is allowed in the EDN format, but also restricts you from using keywords used by the Eden language, and symbols beginning with a dot (ex. ~.name ~.foo), since this is used to access collection properties.

;; Allowed

x y foo bar is-value? set-value! $hallo

;; Not Allowed

for in .foo .bar end

6.3 Statements

6.3.1 Assignment

Assignment in Eden is similar to languages like lua, or python. The most basic form of assignment is assigning a value to a global variable:

<identifier> = <value>

x = 12
foo = :bar
chk? = false

Global variables live for the duration of the program, and can be accessed from anywhere in the program.

The second form of assignment is assigning to a local variable:

local <identifier> = <value>

local x = 12
local foo = :bar
local chk? = false

6.3.2 Conditional Structure

The first and most often used control structure is the if control structure:

;; if structure
if <condition> then
  <truthy body statements...>
end

;; if-else structure
if <condition> then
  <truthy body statements...>
else
  <falsy body statements...>
end

;; if-elseif-else structure
if <condition> then
  <body...>

elseif <condition> then
  <body...>

[elseif <condition> then
  <body...>]...

else
  <body...>
end

Examples

local age = 12
if age < 21 then
  println("You are underage")
end

chk? = true
if chk? then
  println("Value is true")
else
  println("Value is false")
end

6.3.3 While Statement

While statements check its condition, and upon determining that it’s true, will run the block of statements contained in its body. Each time, it will check the condition and call the statment block forever until the condition becomes false.

while <condition> do
  <body...>
end

Examples

;; keep looping until `i` is greater than or equal to 10
local i = 0
while i < 10 do
  println("i: " i)
  i = i - 1
end    

;; this will loop forever
while true do
  println("Never gonna give you up")
end

6.3.4 Repeat-Until Statement

Repeat statements are similar to the while statement, with the differences being that the body is guaranteed to always be called at least once, and the body will be looped over only if the condition is false.

repeat
  <body...>
until <condition>

Examples

;; keep looping until 'i' is greater than or equal to 10
local i = 1
repeat
  println("i: " i)
  i = i + 1
until i >= 10

;; this will loop forever
repeat
  println("Never gonna let you down")
until false

6.3.5 For Statement

The first for statement representation closely resembles the for statement seen in C-based programming languages:

for <iter-var> = <start> <end> [step] do
  <body...>
end

Examples

;; loop from 0 to 10
for i = 0 10 do
  println("i: " i)
end

;; loop from first index to the length of the vector
local x = [1 2 3]
for i = 0 count(x) do
  println(i "-" x[i])
end

;; provide a step
for i = 0 10 2 do
  println("i: " i)
end

The second type of for statement is called the for-each statement. This is the more popular, and more often used loop conditional.

for <iter-var> in <collection> do
  <body...>
end

Examples

;; Print out each element of xs
local xs = [1 2 3]
for x in xs do
  println("Element: " x)
end

6.4 Expressions

6.4.1 Arithmetic Operators

Addition

+

Subtraction

-

Multiplication

*

Division

/

println(2 + 2)
println(2 + 2 - 2)
println(2 * 2 - 5)
println((2 + 2) * 4)
println((2 / 2) * 5)

6.4.2 Coercions & Conversions

Arithmetic performed between integer values will remain as integers. It is only if you include a float within an arithmetic operation that it is automatically converted into a float value.

Almost all types can be converted into a string using the str function.

println(2 + 2) ;; 4 (integer)
println(2 + 2.) ;; 4. (float)

6.4.3 Relational Operators

Equality

==

Inequality

!=

Less Than

<

Greater Than

>

Less Or Equal Than

<=

Greater Or Equal Than

>=

println(2 == 2) ;; true
println(2 != 1) ;; true

local age = 12

println(age < 18) ;; true
println(age > 18) ;; false

6.4.4 Logical Operators

And Operator

and

Or Operator

or

10 or 20 ;; 10
nil or "a" ;; "a"
nil and 10 ;; nil
nil or 10 ;; 10
10 and 20 ;; 20

6.4.5 Length and Concatenation

Unlike Lua, eden does not make use of special operators for length or concatenation. Instead, length can be obtained by using the function count, and concatentation can be performed by using concat.

count([1 2 3]) ;; 3
count("test") ;; 4

concat([1 2 3] [4 5 6]) ;; (1 2 3 4 5 6)

6.4.6 Precedence

Precendence is in this order (similar to lua):

• or, and
• <, >, <=, >=, !=, ==
• +, -
• *, /
• unary operators (-, not)

println(2 + 2 * 4) ;; 10

6.4.7 Collection Construction

Constructing each of the main collections is straightforward

6.4.7.1 Vector

• [1 2 3]
• vector(1 2 3)
• apply(vector list(1 2 3))
• to convert a collection to a vector, use vec

6.4.7.2 Map

• {:a 123 :b (2 + 2)}
• to convert a collection to a map, use into

  into({} [[:a 123] [:b "test"]])
      

6.4.7.3 Set

• #{:a :b :c}
• to convert a collection to a set, use set

6.4.7.4 List

• list(1 2 3)
• apply(list [1 2 3])
• to convert a collection to a list, use into

  into(list() vector(1 2 3 4))
      

6.4.8 Function Calls

Function calls are similar to lua:

<identifier>([arguments...])

Examples

x("test") ;; call the function in variable 'x' with the argument "test"

6.4.9 Function Definitions

Function creation can either be done standalone, or an anonymous function be assigned to a variable:

function add(x y)
  return x + y
end

add = function(x y)
  return x + y    
end

In both cases, they can be assigned to a local variable

local function add(x y)
  return x + y
end

local add = function(x y)
  return x + y
end

6.5 Module System

eden has a simple module system. eden will look for files in order of increasing precedence:

• If on linux, in /usr/share/eden/libs
• If on linux, it will look in each of the colon separated paths in the Environment Variable EDEN_MODULE_PATH
• if on windows, it will look in each of the semi-colon separated paths in the Environment Variable EDEN_MODULE_PATH
• In your home folder, located at ~/.eden/libs (%HOME%/.eden/libs on windows)
• The current working directory

As an example, assuming I have a file named test.eden in the current working directory:

;; test.eden

local print-hello = function(name)
  println(str("Hello " name "!"))
end

export {:hello print-hello}

importing the module is simple:

;; another_file.eden

test = require "test"

test.hello("Ben")

$ eden another_file.eden
Hello Ben!
$ 

6.6 Standard Libraries

Most of the standard libraries are handpicked community libraries that i’ve used in my other projects. The core libraries closely resemble the libraries seen in clojure

6.6.1 Core Library

Most of the clojure core library has been implemented in Eden as a core library. The complete list of clojure.core can be found here. Any dynamic variables, or macros have not been included from the core library.

6.6.2 system Library

system.env(s)

Get the Environment Variable by the name s

system.exit(n)

Return from program with Exit Code n

system.get-globals()

Return all of the Eden program’s global variables. Note that the keys are represented as symbols.

system.set-global(name value)

Set global variable programmatically.

6.6.3 string Library

The Eden string library is a direct mirror of the cuerdas string library. Please refer to the provided page for the list of functions, which can be accessed via the string variable.

Examples

string.caseless=("Hello There!" "HELLO There!") ;; true
string.human(:great-for-csv-headers) ;; "great for csv headers"

6.6.4 filesystem Library

The Eden filesystem library is a direct mirror of the Raynes.fs filesystem library. The library api can be found here.

6.6.5 io Library

The Eden io library is a copy of the clojure.java.io library.

6.6.6 $, Specter Library

For data transformations, the popular specter library has been included in the variable $

Examples

$.setval([:a $.END] [4 5] {:a [1 2 3]}) ;; {:a [1 2 3 4 5]}

$.transform([$.filterer(odd?) $.LAST] inc range(1 9)) ;; (1 2 3 4 5 6 8 8)

$.transform($.ALL inc #{1 2 3}) ;; #{2 3 4}

6.6.7 Parsing Libraries

6.6.7.1 html Library

html.parse(s)

Parses HTML string using hickory (generates hiccup style collection)

html.stringify(coll)

Creates HTML string from collection using hiccup

Also has css generator provided by garden

html.css.gen-css(coll)

provided by garden.core/css

html.css.gen-style(coll)

provided by garden.core/style

html.css.color

several color functions from garden.color

html.css.units

several unit functions from garden.units

6.6.7.2 json Library

JSON library provided by cheshire

json.parse(s [opts])

provided by cheshire.core/parse-string

json.stringify(coll [opts])

provided by cheshire.core/generate-string

6.6.7.3 edn Library

EDN library parser provided by tools.reader

edn.parse(s [opts])

provided by clojure.tools.reader.edn/read-string

edn.stringify(coll [opts])

clojure.core/pr-str

6.6.7.4 markdown Library

Markdown library stringifier provided by markdown-clj

~markdown.stringify(s)

provided by markdown-clj.core/md-to-html-string

6.6.7.5 transit Library

Transit Reader and Generator provided by transit-clj

• transit.parse(s)
• transit.write(x)

6.6.8 http Library

HTTP Server provided by http-kit HTTP Client provided by clj-http-lite HTTP Router provided by bidi

http.router.make-handler(coll)

provided by bidi.ring/make-handler

http.server.run-server(handler [opts])

provided by org.httpkit.server/run-server

http.client.get(url [opts])

provided by clj-http.lite.client/get

Example found at ./examples/eden/http_server.eden

6.6.9 shell Library

Shell library provided by conch, unfortunately it doesn’t work due to reflection issues that will be resolved in future native executables

6.6.10 operator Library

Includes all of the clojure equivalent operators. Useful for additional performance in certain applications

operator.add(x ...)

clojure.core/+

operator.sub(x ...)

clojure.core/-

operator.mult(x ...)

clojure.core/*

operator.div(x ...)

clojure.core//

operator.not(x)

clojure.core/not

operator.and(x y)

clojure.core/and, 2-arity wrapped macro

operator.or(x y)

clojure.core/or, 2-arity wrapped macro

7 Dark-corners of Eden

Since eden uses EDN data values directly, it does mean some funky things can happen unexpectedly.

7.1 Vectors get confused as indexes

map(inc [1 2 3])

This says get the index [1 2 3] of inc. The equivalent in clojure would be (get-in inc [1 2 3]), which is not what we want. The solution is to use the vector function.

map(inc vector(1 2 3))

Note that indexing is only in effect after identifiers and function calls

x[1] ;; indexing
list([1 2 3] x) ;; not indexing
list([1 2 3] x [2]) ;; x[2] is an index!

7.2 The EDN parser gets confused with complex map hashes

local x = {
  :x 2 + 2
  :y 3 - 2
}

The parser will fail, since the resulting map within eden appears as {:x 2, '+ 2, :y 3, '- 2}. The solution is to group each expression in round brackets:

local x = {
  :x (2 + 2)
  :y (3 - 2)
}

;; similarly for functions
local y = {
  :hello (function(name) return str("Hello " name "!") end)
}

8 Differences between Lua and Eden

8.1 Array Indexing

eden uses zero-indexing for array types, whereas lua uses one-indexing for array types.

-- Lua
x = {"A", "B", "C"}
print(x[1]) -- A

;; eden
x = ["A" "B" "C"]
println(x[1]) ;; B

8.2 Equality Symbols

Lua uses = to represent inequality, whereas Eden uses ~!=

-- Lua
print(true ~= false) -- true

;; eden
println(true != false) ;; true

8.3 Module Systems

eden adopts a module system with the special keyword export for exporting, whereas Lua reuses return to represent the module export.

-- Lua
local x = {}
x.test = function()
  print("test!")
end

return x

;; eden
local x = {}
x.test = function()
  println("test!")
end

export x

9 Development

9.1 Uberjar

To generate a standalone uberjar file, run lein uberjar

The generated jar file will be located in ./target/eden-<version>-standalone.jar

9.2 Native Executable Distribution

Please read the Makefile for instructions on how to native compile eden using GraalVM.

9.2.1 Debian DPKG (Tested on Ubuntu 17.10)

make dpkg

9.2.2 Redhat RPM (Tested on Fedora 28)

make rpm

9.2.3 Tar Archive (Tested on Ubuntu 17.10)

make tar

9.3 Testing

Tests can be run with lein test

10 Features for Version 1.0.0 Stable Release

• Test Coverage for the entire standard language
• Better parser errors (might require a parser rewrite)
• support ‘elseif clause in if conditionals (added in 0.4.0-SNAPSHOT)
• Additional standard libraries. (Several libraries have been added since 0.5.0-SNAPSHOT)
• clojure.string (or use funcool.cuerdas, can it native compile?) (added in 0.3.0-SNAPSHOT)
• json parse and stringify libs (one that native compiles) (added in 0.3.0-SNAPSHOT)

11 Future Unreachable(?) Goals

• eden repl
• clojurescript build with passing tests
• metafunctions
• lua table implementation
• natively compiled database interface (sqlite, psql)