============
Architecture
============

.. TODO(lb): https://github.com/langston-barrett/czz/issues/107

.. important::
   This page is intended for the developers of czz and the very curious---it is
   not necessary for users.

czz is implemented as a collection of Haskell libraries. There are four
first-party libraries, which correspond directly to some of the top-level
directories in the czz source tree.

- czz, AKA czz core:

  * Description: generic :doc:`fuzzing algorithm <fuzzing>`, language-agnostic
    mutations

- czz-jvm:

  * Description: JVM-specific wrapper for czz core
  * Depends on: czz

- czz-llvm:

  * Description: :doc:`LLVM-specific system model <llvm/model>`, mutations,
    wrapper for czz core
  * Depends on: czz

- czz-llvm-tui:

  * Description: terminal user interface (TUI) for czz-llvm
  * Depends on: czz, czz-llvm

The dependencies of these libraries include the Haskell standard library
``base``, a few utility libraries such as ``containers`` and ``time``, and, most
notably, Crucible.

`Crucible <https://github.com/GaloisInc/crucible>`_ is a library for the
symbolic execution of imperative programs. It provides a core Crucible
intermediate representation (IR) with language-specific extensions. czz-jvm
translates programs into the Crucible-JVM IR, whereas czz-llvm translates them
into the Crucible-LLVM IR. The functionality in czz core is polymorphic over
(i.e., agnostic to) the Crucible IR extension. While Crucible is capable of
symbolic execution, czz only uses it for concrete execution.