ELLS

Embeddable Lisp-Like Scripting project.

Installation

Just add artifact to your dependencies: "io.github.nihirash" %% "ells" % <latest version>

Usage

Quick start guide

Simplest way to begin is this part of code:

import com.nihirash.ells.{Env, Eval, Interpreter}

val eval = new Eval()
val env = Env.preDef
val interpreter = new Interpreter(eval, env)

interpreter.run(
    """
      |(defn hello (name)
      | (string-append "hello " name))
      |
      | (hello "world")
    """.stripMargin).map(r => println(r.result))

And You'll get hello world on your console.

Predefined forms and default evaluator

If You'll use default evaluator there will be something like "standard library" for ELLS.

You may define yourself evaluator with your custom forms, and/or use some of default forms of ELLS.

Information about standard forms present in docs/forms folder.

Default predefined environment made by evaluating src/main/resources/stdlib.ells file. Please look into it for more information about predefined environment.

Our custom special forms and evaluator

To make your special forms/bindings to scala you must create class with extending com.nihirash.ells.lib.SpecialForm trait.

Simplest example of custom special forms:

  class CustomForm(val eval: (EllsType, Env) => EllsType) extends SpecialForm {
    import com.nihirash.ells.Implicits._

    override def call(id: EllsIdentifier, args: List[EllsType], env: Env): Option[EllsType] = id.v match {
      case "print" => Some {
        val text = args.map(eval(_, env)).mkString("").toString
        println(text)
        text
      }
      case _ => None
    }
  }

Now we need evaluator that's support our special form. For this we need only append our new special form to forms sequence in new evaluator class:

class MyEval extends Eval {
  override val forms: Seq[SpecialForm] = baseForms :+ new CustomForm(eval)
}

And there now we can use it:

object Example extends App {

  val eval = new MyEval
  val env = Env.preDef
  val interpreter = new Interpreter(eval, env)

  interpreter.run(
    """
      |(defn hello (arg)
      | (string-append "hello, " arg "!"))
      |
      |(defn say-hello! (arg)
      | (print (hello arg)))
      |
      |(say-hello! "world")
    """.stripMargin)
}

Sample app

Small example of embedding ELLS is present here

Contributing

If you want to contribute to a project and make it better, your help is very welcome. Any contributions are welcome - misspell fixes, code or documentation improvements and any other.

Legal

Copyright (c) 2018 Alexander Sharihin. All rights reserved.