The CafeSat SMT solver for Scala
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README.md

CafeSat

This is the official repository for the CafeSat source code. CafeSat is a SAT/SMT solver written entirely in Scala. CafeSat attempts provides an efficient command-line tool to solve SMT problems, as well as a library for Scala programs that need the capabilities of SAT/SMT solvers.

Getting Started

CafeSat is built with sbt.

A jar file that can be integrated to another project can be generated with:

sbt package

If you wish to run CafeSat as a standalone tool, the jar file can be executed using the JVM. You need to invoke the cafesat.Main class.

The prefered way to use CafeSat as a standalone tool is to generate a runner script:

sbt cafesat

Then you can run CafeSat as follows:

./target/cafesat [ OPTIONS ] [ INPUT ]

To test that the build went fine, you can, for example, try to solve a Dimacs SAT instances:

./target/cafesat --dimacs input.cnf

Overview

CafeSat is a SAT and SMT solver written entirely in Scala. Its principal aim is to provide a set of safe and well-understood logic solvers useable from a high level programming language such as Scala. The typical approach used in tools needing automated reasoning is to rely on an exeternal executable (usually implemented from C/C++). This has the drawback of needing some external dependencies, and also having part of the computation living outside of the JVM. Some solvers provide an API, which can enable finer integration between the tool and the solvers, but does not solve the issue of having dependencies to native code.

With CafeSat, your Scala/Java application can live entirely in the JVM while still using a powerful and efficient solving procedure. What you get is then less overhead for not needing native bindings from the JVM to the system, and a much safer control of the processes, by opposition to a native code that could generate segmentation fault and crash in a non-recoverable state.

There are several sorts of theorem provers available. The advantage with SMT solvers is that they are very predictable, compared to most other families of provers. They have a well defined input theories, and pack specialized procedure to solve problems in those theories. Unless specified otherwise, the problem they are solving is decidable. The only unpredictable part is that the general problem is NP-complete, which means that it could run for a very long time on some instances. But the general design of an SMT solver is such that it is exteremely efficient on any valid input, and so, in my opinion, works much better when integrated in a bigger workflow, than say a general theorem prover that relies on inference rules.

Documentation

CafeSat has been designed to be used in two distinct ways. The first one is the classical command-line interface, which could be used manually to play with some formulas, or as part of some scripting tasks. The second one is as part of a bigger Scala application, with an API. With the API you get direct access to some low level implementation part of the solver, which gives you the possibility to customize it to your needs. The solver will also live in the same JVM as your main application, and so you will get very precise control.

Command Line

The basic template for using CafeSat as a command line is:

cafesat [ OPTIONS ] [ INPUT ]

OPTIONS can actually be interleaved with the INPUT and the exact ordering does not matter.

INPUT is a filename and is facultative, if none is provided, then CafeSat will read from the standard input. In some sense, providing INPUT is just a convenient shortcut, as an equivalent behaviour could be obtained with input redirection:

cafesat [ OPTIONS ] < cat INPUT

By default, CafeSat expects the input to be a problem in SMT-LIB 2.5, but this behaviour can be overriden with the --dimacs option for reading SAT problem in DIMACS format. CafeSat will output results to the standard output, the result depending on the input problem, but usually would be a single textual output such as sat or unsat. Logging will by default go to the standard error, so one can filter any logging information using a pipe redirection as well. The default logging level is warning, and usually should be quite silent. Logging level can be specified using the option --loglevel=[1-5]. In general, if combining CafeSat into a pipeline of tools, it is possible to parse the problem results by ignoring the standard error (where logging goes) and only considering the content of the standard output (where solving result) goes. Solving result format is well defined for SMT-LIB script, so it is possible to build a stable pipeline.

Scala API

CafeSat exports an API usable from Scala programs. The API is not stable yet and is expected to change frequently. It will NOT be backward compatible.

A minimal Scala doc is available here.

The best way to learn the API is probably to look at some projects relying on CafeSat:

Be sure to check which version of the library is used on each project.

Literature

CafeSat has been first presented in the Scala'13 workshop. However, note that the content of the paper is starting to get out of date.

Licence

CafeSat is distributed under the terms of The MIT License.

All source code in this repository is distributed under this license. The reference text is in the file LICENSE, no copy of the text shall be included in any of the source file, but it is implicitly assumed they are available under the terms specified in LICENSE.

BY COMMITTING TO THIS REPOSITORY, YOU ACCEPT TO RELEASE YOUR CODE UNDER THE TERMS OF THE MIT LICENSE AS DESCRIBED IN THE LICENSE FILE.

Copyright

The copyright for each portion of code is owned by the respective committer, based on the git history. There is no per file or per function copyright as this does not make sense in general. Sorry to be picky, but that's copyright law for you. More information can be found in the COPYRIGHT.md file. Each copyright owner implicitly distributes all code in this repository under the MIT License.