::formally

The open-source formal methods toolchain

::formally is a project that aims to build a comprehensive open-source framework and toolchain to help the development of formal methods applications.

What the project currently provides

The project is still in its very early stages and is in active development. These early releases is meant to be a preview of where the project is going and the start of an open development process for the project.

What the project does currently provide consists in the following:

1. formally::support provides common facilities useful for the rest of the project. Crucially, it provides a mechanism of error reporting based on the concept of diagnostic, similar to what seen in many modern compilers, and facilities to produce precise and informative error messages throughout the project.
2. formally::io provides utilities to parse input and produce output. The main part of the module is a parser combinators library that allows easy and quick writing of parsers that automatically produce precise and high-quality error messages, integrated with the project's error reporting infrastructure.
3. formally::smt provides an abstraction over Satisfiability Modulo Theories solvers and (what will hopefully become) a fully conformant implementation of the SMT-LIBv2 language.
4. A simple toy command-line frontend to test the formally::smt module.

The formally::smt module is quite under heavy development but can already handle simple SMT-LIBv2 scripts, solving them with a Z3 backend.

How to build the crate

The Z3 backend is based on the z3_sys crate which does not discover Z3's library automatically, so we currently need to set include paths and linker arguments manually.

This is done by setting the Z3_SYS_Z3_HEADER environment variable with the path to z3.h and passing the correct -L flag to the compiler to find the shared library.

This can be done conveniently and once and for all by adding the following lines to Cargo's config.toml (see the Configuration section in the Cargo Book):

For example, supposing Z3 has been installed with Homebrew on a macOS system:

[env]
Z3_SYS_Z3_HEADER="/opt/homebrew/Cellar/z3/4.15.3/include/z3.h"

[build]
rustflags=["-C", "link-arg=-L/opt/homebrew/Cellar/z3/4.15.3/lib/"]
rustdocflags=["-C", "link-arg=-L/opt/homebrew/Cellar/z3/4.15.3/lib/"]

Version numbers have to be changed accordingly, of course.

Then, one can add the crate to their own project's dependencies as usual:

$ cargo add formally

How to run the command-line frontend

The front-end can be installed through the formally-cli package.

$ cargo install formally-cli

Then, the formally command accepts a solve subcommand with the name of an SMT-LIBv2 file to run.

$ cat test.smtlib
(set-logic ALIA)
(declare-const array (Array Int Int))

(assert (not (= (select (store array 0 42) 0) 42)))

(check-sat)

$ formally solve test.smtlib
unsat