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A Perl 6 compiler targetting the CLR with an experimental focus on optimizations.
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This is 'Niecza', which is a Perl 6 implementation focusing on optimization and efficient implementation research. It targets the Common Language Runtime (ECMA-335; implementations are "Mono" and ".NET").

For a list of supported features, see


  • To run on Mono: 2.6.4 and later are well-tested, though success has been reported with 2.4.x as well. ggoebel on #perl6 reports that 2.6.7 fails with a bus error on OS X 10.4 x86, but 2.6.4 works; 2.6.7 is fine on other platforms.

    2.8.2 or later is recommended for best performance; you should use RUN_CLR=mono-sgen in this case. 2.10 (latest stable) is also tested.

    Debian and derivatives have a modular mono packaging; you should install 'mono-complete'. (The other packages exist for the sake of Debian-packaged programs.)

    To run on Windows/Mono (2.8.2 and 2.10) and other systems, download the mono installers from

  • To run on Windows/Microsoft .NET 3.5 (2.0 runtime with 3.5 extensions) or .NET 4.0, install the .NET runtime from

    NOTE: Niecza does NOT currently support Windows line endings. Source code (including the setting) must be encoded in Unix format, that is, linefeed only.


All of these need to be available in PATH.

  • Standard Unix utilities (touch, mkdir, rm, cp, echo)
  • wget (to fetch a bootstrapping binary).
  • perl (only needed for testing and the Perl 5 interop layer)
  • GNU make
  • unzip
  • git


    $ make # only if using a source copy
    ... snip build spam ...
    $ mono run/Niecza.exe
    niecza> say 2 + 2
    niecza> ^D
    $ mono run/Niecza.exe -e 'say 2 + 2'

Notes: The first time the compiler is run, the setting must be compiled, which adds about a minute on most hardware to the runtime. The second run will be much faster. Also, the recompilation checker is not robust to file format changes; it may be necessary to clean temporary files after updates.

Building on Windows currently requires the Cygwin environment with Mono's gmcs.exe in your Cygwin shell's $PATH, though in principle .NET's csc.exe could be made to work eventually, if it doesn't already.


Niecza is Copyright 2010-2011 Stefan O'Rear et al. It may be used and distributed under the Artistic License 2.0 (included under LICENSE).

Some files are included from other projects, and have their own copyright notices.


This project was originally a spin-off of experiments done for Matthew "diakopter" Wilson's sprixel project, and was heavily inspired by many of its lower-level details.

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