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https://github.com/geppetto-apps/crow

Transpile/compile Crystal to Flow
https://github.com/geppetto-apps/crow

crystal flow

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Transpile/compile Crystal to Flow

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# [![Crow](logo.png)](https://github.com/geppetto-apps/crow)



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# crow



`crow` transpiles [Crystal][cr] source code to valid [Flow][flow]/ES2015/JavaScript.



Code that is transpiled to valid Flow syntax may be transpiled to valid ES2015,

which may be transpiled to Javascript (via [Babel][babel]).



## Warning: Experimental



This project is in alpha stage and should be considered highly experimental.



## Installation



Via [Homebrew][brew]:



```

brew install geppetto-apps/bin/crow

```



Via [npm][npm]:



```

npm install crow-cli -g

```



## Usage



```sh

# Compiles and outputs to foo.js.flow

$ crow foo.cr



# Same as above

$ cat foo.cr | crow > foo.js.flow



# Compile to JavaScript (via Babel)

$ npm install babel-preset-es2015 babel-plugin-transform-flow-strip-types

$ cat foo.cr | crow | babel --plugins transform-flow-strip-types --presets es2015

```



You can also use [Docker][docker]:



```sh

$ cat foo.cr | docker run -i geppettoapps/crow > foo.js.flow

```



## Motivation & Goal



This is both my first Crystal and first compiler project. I was inspired to learn

more about compilers after reading [Game Programming Patterns' chapter on bytecode][gpp-bytecode]

and also Crystal and its relationship with LLVM. Since Crystal is a high-level,

self-hosted programming language, it's very easy to work with Crystal's internals.

In addition to attempting make Crystal target the web, I've learned a lot about

Crystal from working on this project.



The goal of this project is to make it possible to write both frontend and backend

code for a web project in Crystal; preferably in a way that allows for communication

between native JS and native Crystal code. @asterite from the Crystal Team has

noted that [crystal is not geared against the web](https://github.com/crystal-lang/crystal/issues/829#issuecomment-113955554)

and there's still work left to [make Crystal to work with asm.js][asm-issue].

Due to this `crow` currently approach the problem by using transpilation, but that

may not be the case forever. The only public API for `crow` is the CLI that takes

in some Crystal code and spits out something may run in the browser.



## Milestones



- [ ] [1.0: Run Crystal code in isolation in the browser](https://github.com/geppetto-apps/crow/milestone/1)

- [ ] [1.1: DOM manipulations from Crystal code](https://github.com/geppetto-apps/crow/milestone/2)

- [ ] [1.2: Bind Crystal code to DOM events](https://github.com/geppetto-apps/crow/milestone/3)

- [ ] [1.3: Call Crystal code from Javascript](https://github.com/geppetto-apps/crow/milestone/4)

- [ ] [1.4: Call non-DOM related Javascript code from Crystal ](https://github.com/geppetto-apps/crow/milestone/5)



## Supported AST nodes



Extracted from [Crystal's compiler][cr-parser].



- [x] Expressions

- [x] NilLiteral

- [x] BoolLiteral

- [x] NumberLiteral

- [x] CharLiteral

- [x] StringLiteral

- [x] StringInterpolation

- [x] SymbolLiteral

- [x] ArrayLiteral

- [x] HashLiteral

- [x] NamedTupleLiteral

- [ ] ProcLiteral

- [ ] RangeLiteral

- [ ] RegexLiteral

- [ ] TupleLiteral

- [x] Var

- [x] Block

- [x] Call

- [ ] NamedArgument

- [x] If

- [x] Unless

- [ ] IfDef

- [x] Assign

- [ ] MultiAssign

- [x] InstanceVar

- [ ] ReadInstanceVar

- [ ] ClassVar

- [ ] BinaryOp

- [ ] Arg

- [x] ProcNotation

- [x] Def

- [ ] Macro

- [ ] UnaryExpression

- [ ] VisibilityModifier

- [x] IsA

- [ ] RespondsTo

- [ ] Require

- [x] When

- [x] Case

- [ ] ImplicitObj

- [ ] Path

- [x] While

- [x] Until

- [ ] Generic

- [ ] TypeDeclaration

- [ ] UninitializedVar

- [x] Rescue

- [x] ExceptionHandler

- [ ] ProcPointer

- [ ] Union

- [x] Self

- [ ] ControlExpression

- [ ] Yield

- [ ] Include

- [ ] Extend

- [ ] EnumDef

- [x] ClassDef

- [ ] ModuleDef

- [ ] LibDef

- [ ] FunDef

- [ ] TypeDef

- [ ] CStructOrUnionDef

- [ ] ExternalVar

- [x] Alias

- [ ] Metaclass

- [ ] Cast

- [ ] NilableCast

- [ ] TypeOf

- [ ] Attribute

- [ ] MacroExpression

- [ ] MacroIf

- [ ] MacroFor

- [ ] MacroVar

- [ ] MacroLiteral

- [ ] Underscore

- [ ] MagicConstant

- [ ] Asm

- [ ] AsmOperand



## Contributing



1. Fork it ( https://github.com/geppetto-apps/crow/fork )

2. Create your feature branch (git checkout -b my-new-feature)

3. Commit your changes (git commit -am 'Add some feature')

4. Push to the branch (git push origin my-new-feature)

5. Create a new Pull Request



## Attribution



Logo: [Crow by Encrico Francese][crow-flickr]



## Contributors



- [theodorton](https://github.com/theodorton) Theodor Tonum - creator, maintainer



[cr]: https://crystal-lang.org/

[cr-src]: https://github.com/crystal-lang/crystal

[cr-syntax]: https://github.com/crystal-lang/crystal/blob/master/src/compiler/crystal/syntax/ast.cr

[docker]: https://www.docker.com/

[flow]: https://flowtype.org/

[babel]: https://babeljs.io/

[npm]: https://www.npmjs.com

[brew]: http://brew.sh/

[crow-flickr]: https://www.flickr.com/photos/remanufactory/5553711670

[gpp-bytecode]: http://gameprogrammingpatterns.com/bytecode.html

[asm-issue]: https://github.com/crystal-lang/crystal/issues/535