https://github.com/jxxcarlson/elm-lisp

An experiment in writing parse and eval for a typed Lisp in Elm.
https://github.com/jxxcarlson/elm-lisp

Last synced: 2 months ago
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An experiment in writing parse and eval for a typed Lisp in Elm.

• Host: GitHub
• URL: https://github.com/jxxcarlson/elm-lisp
• Owner: jxxcarlson
• Created: 2020-09-04T04:20:01.000Z (over 4 years ago)
• Default Branch: master
• Last Pushed: 2020-09-08T14:04:06.000Z (over 4 years ago)
• Last Synced: 2024-02-13T09:12:20.813Z (11 months ago)
• Language: JavaScript
• Homepage:
• Size: 43 KB
• Stars: 5
• Watchers: 4
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

Awesome Lists containing this project

• awesome-elm-pltd - elm-lisp - An experiment in writing `parse` and `eval` for a typed Lisp in Elm. (Languages / Interpreters)

README

        
# A Typed Lisp in Elm

The code you find here outlines how one might go about writing

a kind of typed Lisp in Elm — an educational experiment for myself.

The files are

- *Parse.elm*, exporting one type, `AST`, and one function `parse`.

- *ParserHelpers.elm*, exporting one function, `many`, a clip from

  the package [Punie/parser-extras](https://package.elm-lang.org/packages/Punie/elm-parser-extras/latest/).

  The `many` combinator is used in module `Parse`

- *Lisp.elm*, exporting one function, `eval`

- *Lisp2.elm*, a superset of *Lisp.elm*, also exporting `evalToString`

[Medium article on this code](https://medium.com/@jxxcarlson/a-typed-lisp-in-elm-e5c733f63931)

One can evaluate Lisp expressions using `elm-repl` or by using the little node repl program  

described in the last section.

## Using elm-repl  

Examples:

```

$ elm repl

> import Parse exposing(parse)

> import Lisp2 exposing(eval)

> parse "(+ 1 2 3)"

Just (LIST [Str "+",Num 1,Num 2,Num 3])

    : Maybe Parse.AST

> eval "(+ 1 2 3)"

Just (VNum 6) : Maybe Lisp2.Value

> eval "(+ 1 2 haha!)"

Just Undefined : Maybe Lisp2.Value

```

Note that `eval` handles nonsense input in a somewhat graceful way.

## The repl

To use the repl:

```

$ elm make --optimize src/Repl/Main.elm --output=src/Repl/main.js

$ node src/Repl/repl.js

Type ':help' for help

> (+ 1 2)

3

```

The repl program uses the code in `./src/Repl` following the outline

described in the Medium article [Elm as BlackBox](https://medium.com/@jxxcarlson/running-elm-as-a-blackbox-b1930592054b).  The idea is to use the `Platform.Worker` program in `Repl.Main` to communicate with the

terminal via `node.js`.