Roc language preview

1. Hello, world

an app header, backpassing, and string interpolation

horizon-dark

app [main] { pf: platform "https://github.com/roc-lang/basic-cli" }

## Doubles a number
double = \n -> n * 2

main =
    result <- Task.await (Stdout.line "Hello, $(name)!")
    when result is
        Ok _ -> Stdout.line "done"
        Err _ -> crash "failed"

atom-one-dark

app [main] { pf: platform "https://github.com/roc-lang/basic-cli" }

## Doubles a number
double = \n -> n * 2

main =
    result <- Task.await (Stdout.line "Hello, $(name)!")
    when result is
        Ok _ -> Stdout.line "done"
        Err _ -> crash "failed"

github-dark

app [main] { pf: platform "https://github.com/roc-lang/basic-cli" }

## Doubles a number
double = \n -> n * 2

main =
    result <- Task.await (Stdout.line "Hello, $(name)!")
    when result is
        Ok _ -> Stdout.line "done"
        Err _ -> crash "failed"

dracula

app [main] { pf: platform "https://github.com/roc-lang/basic-cli" }

## Doubles a number
double = \n -> n * 2

main =
    result <- Task.await (Stdout.line "Hello, $(name)!")
    when result is
        Ok _ -> Stdout.line "done"
        Err _ -> crash "failed"

nord

app [main] { pf: platform "https://github.com/roc-lang/basic-cli" }

## Doubles a number
double = \n -> n * 2

main =
    result <- Task.await (Stdout.line "Hello, $(name)!")
    when result is
        Ok _ -> Stdout.line "done"
        Err _ -> crash "failed"

github

app [main] { pf: platform "https://github.com/roc-lang/basic-cli" }

## Doubles a number
double = \n -> n * 2

main =
    result <- Task.await (Stdout.line "Hello, $(name)!")
    when result is
        Ok _ -> Stdout.line "done"
        Err _ -> crash "failed"

2. Pattern matching

when/is with Ok and Err tags

horizon-dark

describe = \num ->
    when num is
        0 -> "zero"
        n if n < 0 -> "negative"
        _ -> "positive"

atom-one-dark

describe = \num ->
    when num is
        0 -> "zero"
        n if n < 0 -> "negative"
        _ -> "positive"

github-dark

describe = \num ->
    when num is
        0 -> "zero"
        n if n < 0 -> "negative"
        _ -> "positive"

dracula

describe = \num ->
    when num is
        0 -> "zero"
        n if n < 0 -> "negative"
        _ -> "positive"

nord

describe = \num ->
    when num is
        0 -> "zero"
        n if n < 0 -> "negative"
        _ -> "positive"

github

describe = \num ->
    when num is
        0 -> "zero"
        n if n < 0 -> "negative"
        _ -> "positive"

3. Pipelines

the |> operator chaining function calls

horizon-dark

total =
    [1, 2, 3]
    |> List.map (\n -> n * 2)
    |> List.sum

atom-one-dark

total =
    [1, 2, 3]
    |> List.map (\n -> n * 2)
    |> List.sum

github-dark

total =
    [1, 2, 3]
    |> List.map (\n -> n * 2)
    |> List.sum

dracula

total =
    [1, 2, 3]
    |> List.map (\n -> n * 2)
    |> List.sum

nord

total =
    [1, 2, 3]
    |> List.map (\n -> n * 2)
    |> List.sum

github

total =
    [1, 2, 3]
    |> List.map (\n -> n * 2)
    |> List.sum