Haste

A compiler to generate Javascript code from Haskell.

Features

• Generates small, fast programs
• Supports all GHC extensions except Template Haskell
• Uses standard Haskell libraries
• Cabal integration
• Concurrency and MVars with Haste.Concurrent
• Unboxed arrays, ByteArrays, StableNames and other low level features
• Low-level DOM base library
• Easy integration with Google's Closure compiler
• Works on Windows, GNU/Linux and Mac OS X
• Simple, one-step build; no need for error prone Rube Goldberg machines of Vagrant, VirtualBox, GHC sources and other black magic

Installation

You have two options for getting Haste: installing from Hackage or from Github. In both cases, you need to add add Cabal's bin directory, usually ~/.cabal/bin, to your $PATH if you haven't already done so.

Then, installing the latest stable-ish version from cabal is easy:

$ cabal install haste-compiler
$ haste-boot

Building from Github source is equally easy. After checking out the source, cd to the source tree and run:

$ cabal install
$ haste-boot --force --local

You should probably run the test suite first though, to verify that everything is working. To do that, execute ./runtests.sh in the Haste root directory. You may also run only a particular test by executing ./runtests.sh NameOfTest. The test suite uses the nodejs interpreter by default, but this may be modified by setting the JS environment variable as such: JS=other-js-interpreter ./runtests.sh. Other JavaScript interpreters may or may not work.

Haste has been tested to work on Windows and OSX platforms, but is primarily developed on GNU/Linux. As such, running on a GNU/Linux platform will likely get you less bugs.

Usage

To compile your Haskell program to a Javascript blob ready to be included in an HTML document or run using a command line interpreter:

$ hastec myprog.hs

This is equivalent to calling ghc --make myprog.hs; Main.main will be called as soon as the JS blob has finished loading.

You can pass the same flags to hastec as you'd normally pass to GHC:

$ hastec -O2 -fglasgow-exts myprog.hs

Haste also has its own set of command line arguments. Invoke it with --help to read more about them. In particular --opt-all, --opt-google-closure and --with-js should be fairly interesting.

If you want your package to compile with both Haste and, say, GHC, you might want to use the CPP extension for conditional compilation. Haste defines the preprocessor symbol __HASTE__ in all modules it compiles.

Haste also comes with wrappers for cabal and ghc-pkg, named haste-inst and haste-pkg respectively. You can use them to install packages just as you would with vanilla GHC and cabal:

$ haste-inst install mtl

This will only work for libraries, however, as installing Javascript "executables" on your system doesn't make much sense. You can still use haste-inst build to build your "executables" locally, however.

Finally, you can interact with Javascript code using the FFI. See doc/js-externals.txt for more information about that.

For more information on how Haste works, see the Haste Report, though beware that parts of Haste may have changed quite a bit.

You should also have a look at the documentation and/or source code for haste-lib, which resides in the libraries/haste-lib directory, and the small programs in the examples directory, to get started.

Reactive web EDSL

Haste comes with a basic, environment for writing client side web applications in a reactive fashion. See Fursuit for more information.

As the reactive library relies heavily on Applicative, you may find the idiom brackets of the Strathclyde Haskell Enhancement (https://personal.cis.strath.ac.uk/~conor/pub/she/) quite useful.

Libraries

Haste is able to use standard Haskell libraries. However, some primitive operations are still not implemented which means that any code making use of them will give you a compiler warning, then die at runtime with an angry error. This is currently being worked on.

Why yet another Haskell to Javascript compiler?

Existing implementations either produce huge code, require a fair amount of work to get going, or both. With Haste, the idea is to give you a drop-in replacement for GHC that generates relatively lean code.

Known issues

• No 64-bit math yet. Use Integer if you need large integers.

• Not all GHC primops are implemented; if you encounter an unimplemented primop, I'd be happy if you'd report it together with a small test case that demonstrates the problem.

• A program that throws unhandled exceptions may not always give a nice error message.