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A Rail compiler written in Haskell Build Status

This is (or rather: will become) a compiler for the esoteric programming language Rail, written in Haskell.

Contents of this repository

  • documentation contains additional documentation.
    • The main documentation will be found in the code.
  • src contains the Rail compiler and editor (written in Haskell).
  • tests contains the hunit tests
  • integration-tests contains integration tests
    • see section tests for more information.


If you plan to contribute to the project, make sure that your contribution does not break any tests and hlint is happy.

Coding conventions

Though not applied consistently until now, there are some things which would be really NICE to have:

  • Set indetations to 2 spaces
  • Remove trailing white spaces
  • Do not retab/reformat other people's code, especially not in a commit which contains some logical changes as well
  • One logical change per commit
  • Integrate hlint to your editor of choice and try to stick to the suggestions it makes
  • Would be cool, if lines are not longer than 80 characters

Module testing with HUnit

tests contains a Main.hs file that runs an HUnit test with a list of test functions. For each module src/[module-name].hs of the compiler pipeline exists a corresponding test file tests/T[module-name].hs exporting a list of test functions for the named module. In the Main.hs file the list that is tested by HUnit, is concatenated by the exported test lists of all test modules.

Integration tests

Integration tests are stored in integration-tests in three subdirectories:

  • passing/ contains tests that are testing already implemented features and that already passed before
  • failing/ contains tests that are testing already implemented features but never passed
  • future/ contains tests that are testing functionality that will be added in the future

Each test consists of two files. A rail program [test-name].rail and an io-file [test-name].io.

The io-file specifies test cases, i.e. a set of inputs with the expected corresponding outputs of the rail-program.

Input and output as well as the test cases themselves are separated by a hash tag. If an input has more than one value, they are separated by a newline. Consider a rail program adding two numbers and printing the result (without any newlines). A corresponding io-file with two test cases could look as follows:


NOTE 1: printed newlines have to be stated explicitly. Consider a hello-world program printing Hello World\n (without any input). The io-file has to look as follows:

Hello World\n

NOTE 2: The expected output is only tested against stdout. If you want to test the output on stderr as well, you can add another section to a test case, separated by a single % line:

This is the input.
This is the expected output on stdout.
This is the expected output on stderr.
Another input.
Another stdout output.

NOTE 3: Lines containing only a single % or # character always delimit sections as described above. There is no way to escape them, sorry.

tests/integration_tests.sh is a script written in bash. It iterates over all rail programs in passing/, compiles each of them using the current version of our rail compiler and retrieves runnable llvm-code, i.e. it already links it with the stack implementation, etc. For each input/output value, it puts the input into the llvm-binary and compares the actual output with the current output. The result will be printed to stdout.

Dependencies / Building the Compiler

  • Install cabal (package cabal-install in most distributions)
  • Install llvm, versions llvm-3.3 and llvm-3.4 work.
  • run cabal update
  • If you don't use llvm-3.4 you manually need to install the corresponding haskell bindings, i.e.: cabal install llvm-general-
  • Switch to project folder
  • Run cabal install --enable-tests to install all dependencies and build the project
  • cabal test to run the tests
  • Run the compiler with dist/build/SWPSoSe14/SWPSoSe14 -c -i <Source.rail> -o output
  • You still need to link the stack manually if you want to have executables: llvm-link <compiled.ll> src/RailCompiler/*.ll -o executable


You can generate the compiler documentation using cabal haddock --executables --haddock-options --ignore-all-exports from the root project directory.

Branching model

Currently, there are several (long-lived) team branches and one main development branch, master. The master branch should always contain something that "works" to some degree, i. e. it should never break.

All team branches are merged into the master branch on a regular basis.

Team branches

The following team branches exist. Except for master, all branches not mentioned here are to be considered (short-lived) feature branches.

  • gui: Contains everything with a graphical user interface, most notably the debugger and the graphical Rail editor.
  • intertarget-code: Contains code for the backend, for intermediate code generation and for code optimization.
  • preproc-lexer: Contains code for the preprocessor and lexer components.
  • synsem-analysis: Contains code for the syntactic/semantic analysis.

Additional Information

For additional information take a look at our wiki pages: https://github.com/SWP-Ubau-SoSe2014-Haskell/SWPSoSe14/wiki