Platform.worker

This is a little experiment to learn how to use Elm's Platform.worker for simple command-line programs (CLI).
The worker is a kind of "black box" which accepts input from a command-line program via ports, computes a value from the input, and sends it back by the same method. There are two versions, described below: a one-shot version, and a repl.

I would like to thank @pd-andy, @urban-a and @jfmengels on the Elm Slack for their help. I was also inspired by Punie's article on his simply-typed lambda calculus interpreter and the code for it.

Installation

$ sh make.sh

Using the one-shot CLI

 $ node src/cli.js 47

> platform@1.0.0 cli /Users/carlson/dev/elm/experiments/platform
> node src/cli.js "47"

   Input:  47
   Output: 142

Note. Input is transformed to output in the Elm app Main.elm using the function

transform : InputType -> OutputType
transform k =
    case modBy 2 k == 0 of
        True -> k // 2
        False -> 3*k+ 1

where InputType and OutputType are aliases for Int. In words,

If the input is even, divide it by 2. If it is odd, multiply it by 3 and add 1.

To do something more interesting, replace the function transform (and if need be, the types).

Using repl

 $ node src/repl.js

> platform@1.0.0 repl /Users/carlson/dev/elm/experiments/platform
> node src/repl.js

> 47
142
> 142
71
> 71
214
>

What happens if you continue with the above?

Note: There is a related command-line interpreter in this repo. The command load foo.txt loads the contents of ./foo.txt into memory. The command show displays the contents of the file in memory.

Note to self: This code is found at ~/dev/elm/experiments/platform

jxxcarlson/elm-platform-worker-example

Platform.worker

Installation

Using the one-shot CLI

Using repl