Alex: A Lexical Analyser Generator

Alex is a Lex-like tool for generating Haskell scanners. For complete documentation, see the doc directory.

• https://www.haskell.org/alex/

• https://hackage.haskell.org/package/alex

Alex version 2.0 has changed fairly considerably since version 1.x, and the syntax is almost completely different. For a detailed list of changes, see the release notes in the documentation.

Alex is now covered by a BSD-Style licence; see the licence file in the 'doc' directory for details.

The sources are in the 'src' directory and the documentation in the 'doc' directory; various examples are in the 'examples' subdirectory.

The source code in the 'src' and 'examples' directories is intended for a Haskell 98 compiler with hierarchical modules. It should work with GHC >= 5.04.

Build Instructions

If you just want to use Alex, you can download or install (via cabal install alex) an Alex release from Hackage; also note that distributions such as the Haskell Platform and other package manager-based distributions provide packages for Alex. Moreover, recent versions of cabal will automatically install the required version of alex based on build-tools/build-tool-depends declarations.

Read on if you want to build Alex directly from Git.

Alex is built using GHC & Cabal; so first install GHC and cabal-install-2.0 (or later).

Since Alex itself is implemented in terms of an Alex scanner, bootstrapping Alex is a bit tricky:

You need to have the build-tools alex and happy manually installed; either via your system package manager distribution, the Haskell Platform, or e.g. via (run this outside the Git repository!):

$ cabal install alex happy

which installs them into ${HOME}/.cabal/bin by default (make sure they're in your $PATH for the next steps!).

Variant A

First you need to generate the pre-processed templates via

$ cabal new-run gen-alex-sdist

(otherwise cabal install will complain about "data/AlexTemplate: copyFile: does not exist (No such file or directory)")

And then you can install alex simply by invoking

$ cabal install

from inside the Git folder.

Variant B

Alternatively, you can use the Makefile which automates the steps of producing a self-contained pre-bootstrapped source distribution with pre-generated lexer/scanners (and which also performs the cabal new-run gen-alex-sdist pre-preprocessing step):

$ make sdist
$ cabal install dist/alex-*.tar.gz

For convenience, there's also a make sdist-test target which builds the source source tarball and runs the test-suite from within the source dist.

Contributing & Reporting Issues

Please report any bugs or comments at https://github.com/simonmar/alex/issues

Share and enjoy,

Chris Dornan: cdornan@arm.com

Isaac Jones: ijones@syntaxpolice.org

Simon Marlow: simonmar@microsoft.com