derw

An Elm-inspired language that transpiles to TypeScript

Install

npm install --save-dev derw

npm install -g derw

Usage

npx derw

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

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

npx 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
  --names :                 Check for missing names out of scope
  --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

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

List ranges [ 1..5 ], [ start..end ]

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

Function calls
```
three = add 1 2
```
Module references
```
three = List.map identity [ 1, 2, 3 ]
```

Union types

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

Type variables
```
type Thing a = Thing a
```
Type aliases
```
type User =
    { name: string }
```
Object literals
```
user: User
user = { name: string }
```

Imports

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

Exports
```
exposing ( map )
```

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

If statements

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

Case..of

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

Destructing in case..of

type User = User { name: string }

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

strings in case..of

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)

Constructing union types

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

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
}
```

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
```

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]
```

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

Importing of Derw files

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

Errors when failing to find relative import

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

Single line comments

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

Single line comments in function or const bodies

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

Multiline comments

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

Function arguments

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

Globals

Globals can be accessed through the globalThis module which is imported into every namespace. E.g globalThis.console.log

1.0.0

An automatic formatter with no options
A standard library
Support for Coed

Use html
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
Package init
```
derw init
```
Package testing
```
# inside a package directory
derw test
```
Compile a package
```
derw compile
```
An info command to find out stats about modules
```
derw init
```
A repl
```
derw repl
```

Bundling

derw bundle --entry src/Main.derw --output dist/index.js --watch --quiet

2.0.0

Time travelling d ebugger
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".

groteck / derw