docs/repl.md · elk · git.iko.soy

git.iko.soy/elk

elk/docs/repl.md

66 lines 1.3 kB history raw

1# `elm repl`

3The REPL lets you interact with Elm values and functions in your terminal.

5<br>

7## Install

9You need [Elm][install] and [node.js][node] for the REPL. Elm generates JavaScript and we currently use node.js to evaluate it!

11[install]: https://guide.elm-lang.org/install.html

12[node]: https://nodejs.org/en/download/

14<br>

16## Use

18You can type in expressions, definitions, union types, and module imports using normal Elm syntax.

20```elm

21> 1 + 1

222 : number

24> "hello" ++ "world"

25"helloworld" : String

26```

28The same can be done with definitions and union types:

30```elm

31> fortyTwo = 42

3242 : number

34> increment n = n + 1

35<function> : number -> number

37> increment 41

3842 : number

40> factorial n = if n < 1 then 1 else n * factorial (n-1)

41<function> : number -> number

43> factorial 5

44120 : number

46> type Either a b = Left a | Right b

48> case Left 32 of \

49| Left n -> 2 * n \

50| Right m -> m + 1

5164 : number

52```

54When you run `elm repl` in a project with an `elm.json` file, you can import any module available in the project:

56```elm

57> import String

59> String.length "hello"

605 : Int

62> String.reverse "flow"

63"wolf" : String

64```

66Core modules, package modules, your modules. Whatever is available! So if you create a module named `MyThing` in your project, you can say `import MyThing` in the REPL and mess with anything it exposes.