derw

An Elm-inspired language that transpiles to TypeScript

Usage

npx @eeue56/derw

To get started:
Start a package via `derw init`
Compile via `derw compile`
Or compile and test via `derw test`

You can run the derw compiler via npx. You must provide files via --files or be in a package directory.

npx @eeue56/derw

Let\'s write some Derw code
To get started:
Provide entry files via --files
Or run me without args inside a package directory
  --files [string...]:      Filenames to be given
  --test :                  Test the project
  --target ts | js | derw:  Target TS, JS or Derw output
  --output string:          Output directory name
  --verify :                Run typescript compiler on generated files to ensure valid output
  --debug :                 Show a parsed object tree
  --only string:            Only show a particular object
  --run :                   Should be run via ts-node/node
  --format :                Format the files given in-place
  --quiet :                 Keep it short and sweet
  -h, --help :              This help text

Example

You can find a bunch of examples in examples, along with the Typescript they generate. But the general gist is: Elm-compatible syntax where possible.

type Result a b
    = Err { error: a }
    | Ok { value: b }

asIs : Result a b -> Result a b
asIs result =
    case result of
        Err { error } -> Err { error }
        Ok { value } -> Ok { value }

Roadmap

0.0.1 alpha

• [x] Arrays [ ], [ 1, 2, 3 ], [ [ 1, 2, 3 ], [ 3, 2, 1 ] ]
• [x] Booleans true, false
• [x] Boolean equality 1 < 2, 1 <= 2, 1 == 2, 1 != 2, 1 > 2, 1 >= 2
• [x] Boolean operations true && false, not true, true || false
• [x] Strings "", "hello world"
• [x] Format strings ``, `Hello ${name}`
• [x] Numbers -1, 0, 1, -1.1, 1.1
• [x] Addition 1 + 2, "Hello" + name
• [x] Subtraction 2 - 1
• [x] Multiplication 2 * 1
• [x] Division 2 / 1
• [x] Pipe [1, 2, 3] |> List.fold add, List.fold add <| [1, 2, 3]
• [ ] Compose >>, <<
• [x] Constants hello = "hello world"
• [x] Function definitions
• [x] Lists [ 1, 2, 3 ], [ "hello", "world" ]
• [x] List ranges [ 1..5 ], [ start..end ]

add : number -> number -> number
add x y = x + y

• [x] Function calls

three = add 1 2

• [x] Module references

three = List.map identity [ 1, 2, 3 ]

• [x] Union types

type Result a b
    = Err { error: a }
    | Ok { value: b }

• [x] Type variables

type Thing a = Thing a

• [x] Type aliases

type User =
    { name: string }

• [x] Object literals

user: User
user = { name: string }

• [x] Imports

import List
import Result exposing ( map )
import something as banana

• [x] Exports

exposing ( map )

• [x] Let statements

sayHiTo : User -> string
sayHiTo user =
    let
        name = user.name
    in
        "Hello " + name

sayHelloTo : User -> string
sayHelloTo user =
    let
        getName: User -> string
        getName user = user.name
    in
        "Hello" + getName user

• [x] If statements

type Animal = Animal { age: number }
sayHiTo : Animal -> string
sayHiTo animal =
    if animal.age == 1 of
        "Hello little one!"
    else
        "You're old"

• [x] Case..of

type Animal = Dog | Cat
sayHiTo : Animal -> string
sayHiTo animal =
    case animal of
        Dog -> "Hi dog!"
        Cat -> "Hi cat!"

• [x] Destructing in case..of

type User = User { name: string }

sayHiTo : User -> string
sayHiTo user =
    case user of
        User { name } -> "Hi " + name + !"

• [x] strings in case..of
• [x] defaults in case..of

sayHiTo : string -> string
sayHiTo name =
    case name of
        "Noah" -> "Hi " + name + !"
        default: "I don't know you"

• [ ] List destructing

sayHiTo : List number -> string
sayHiTo xs =
    case xs of
        [] -> "Empty"
        x::ys -> "Hello " + x + (sayHiTo ys)

• [x] Constructing union types

type User = User { name: string }
noah = User { name: "Noah" }

• [x] Errors on type name collison

The name `Person` has been used for different things.
8 - 10:

```
type Person =
    Person { name: string }
```

11 - 14:

```
type alias Person = {
    name: string
}
```

• [x] Errors on function name collison

The name `isTrue` has been used for different things.
0 - 3:

```
isTrue: boolean -> boolean
isTrue x =
    x == true
```

4 - 7:

```
isTrue: boolean -> boolean
isTrue x =
    x != true
```

• [x] Some form of basic type errors

Failed to parse examples/errors/mismatching_types.derw due to:
Error on lines 0 - 3
Expected `boolean` but got `number` in the body of the function:

```
isTrue: boolean -> boolean
isTrue x =
    1 + 2
```

Error on lines 4 - 7
Expected `List string` but got `List number`:

```
names: List string
names =
    [1..2]
```

• [x] lambdas \x -> x + 1, \x y -> x + y
• [x] Typescript output
• [x] Javscript output
• [ ] Elm output
• [x] Module resolution
• [x] CLI
• [x] Basic type checking
• [x] Detect if types exist in current namespace
• [x] Syntax highlighting for editors
• [x] Collision detection for names in a module
• [x] Importing of Derw files

import "./other"
import "./something" as banana
import "./another" exposing ( isTrue, isFalse )

• [x] Errors when failing to find relative import

Warning! Failed to find `examples/derw_imports/banana` as either derw, ts or js

• [x] Single line comments

-- hello
isTrue: boolean -> boolean
isTrue x =
    x

• [x] Single line comments in function or const bodies

isTrue: boolean -> boolean
isTrue x =
    -- hello
    x

• [x] Multiline comments

{-
hello
world
-}
isTrue: boolean -> boolean
isTrue x =
    x

• [x] Function arguments

map: (a -> b) -> a -> b
map fn value =
    fn value

1.0.0

• [x] An automatic formatter with no options
• [ ] A standard library
• [ ] Support for Coed
• [x] Testing support via Bach

Write a file with _test as an extension (e.g List_test.derw).

import Test exposing (equals)

testMath: boolean -> void
testMath a? =
    equals 1 1

Compile it, then run bach via npx @eeue56/bach

• [ ] Type checking
• [ ] Benchmarking support via Mainc
• [ ] Async support
• [ ] Packaging
• [x] Package init

derw --init

• [x] Package testing

# inside a package directory
derw --test

2.0.0

• [ ] Type checking with interop with TypeScript
• [ ] Derw compiler is written in Derw

Divergence from Elm

• All top level consts or functions must have type definitions
• Format strings ``
• No need for module names in the module file itself. Use exposing instead

Editor language support

Currently VSCode syntax highlighting is supported by this extension: https://github.com/eeue56/derw-syntax. It is not on the marketplace because Microsoft account creation was down when I tried.

Instead, you can do:

git clone https://github.com/eeue56/derw-syntax
cp -r derw-syntax ~/.vscode/extensions/derw-syntax-0.0.1

Name

derw which means oak. Oak is one of the native trees in Wales, famous for it's long life, tall stature, and hard, good quality wood. An English speaker might pronounce it as "deh-ru".