Falderal /

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Falderal is a file format for literate test suites. It is particularly suited for testing and documenting functions which interpret or compile programming languages. The dumbed-down sound-bite version: "doctests for DSLs". Test.Falderal is the reference implementation, in Haskell, of tools for formatting and running tests written in Falderal.

Here's the scenario:

  • You have a file format, or a language (perhaps a programming language) and some rules for processing it (interpreting it, compiling it, etc.)
  • You have functions written (currently) in Haskell which implement these rules.
  • You have some tests for those rules (e.g. program A always produces output B) that you want to present in a nicely readable fashion, possibly included right in your literate programming source file.

If this describes you, then Falderal might help. The particular need I had that encouraged me to write it is having implemented several esoteric programming languages in Haskell, and wanting to write nicely formatted tests suites for them.


The current released version of Falderal is 0.3. It introduced the following features:

  • The definition of a Falderal Literate Test Format, distinct from the reference implementation of tools for it in Haskell (Test.Falderal).
  • The ability to format a Falderal file to different formats, including Markdown and Haskell.
  • Running tests is now a matter of formatting a Falderal file as a Haskell module and running the function testModule in that module.

The previous released version of Falderal is 0.2. It introduced the following features:

  • Added a test harness for Falderal itself, in the form of a simple shell script which diffs the output of Test.Falderal.Demo against a text file containing the expected content.
  • Improved formatting of failure reports. Multi-line input text or expected output is always presented starting on its own line.
  • Tests may be organized into groups; the entire group is preceded by some literal text, but there is no literal text between the tests in the group. When one of these tests fails, the literal text for the group is reported, along with the number of the test within the group.
  • Fixed a bug where exception text which extended over multiple lines could not be expected correctly.

The current version under development is 0.4. It will likely expand upon the potential language-independence that was introduced here by including formatters for other languages, such as Python functions and shell commands. It will likely also attempt to make the usage simpler, possibly by providing an executable front-end, possibly also by being a Cabal package.

The API should not be expected to be stable through the 0.x series.


Falderal development is hosted on Bitbucket:

Bugs may be reported (and features requested) on the Issue Tracker:

Official release distfiles are available on the Falderal project page at [Cat's Eye Technologies'][].

For Further Information

Please see the Falderal wiki on Bitbucket.