easy-smt

About

easy-smt is a crate for interacting with an SMT solver subprocess. This crate provides APIs for

• building up expressions and assertions using the SMT-LIB 2 language,
• querying an SMT solver for solutions to those assertions,
• and inspecting the solver's results.

easy-smt works with any solver, as long as the solver has an interactive REPL mode. You just tell easy-smt how to spawn the subprocess.

Example

```rust use easy_smt::{ContextBuilder, Response};

fn main() -> std::io::Result<()> { // Create a new context, backed by a Z3 subprocess. let mut ctx = ContextBuilder::new() .solver("z3", ["-smt2", "-in"]) .build()?;

// Declare `x` and `y` variables that are bitvectors of width 32.
let bv32 = ctx.bit_vec_sort(ctx.numeral(32));
let x = ctx.declare("x", bv32)?;
let y = ctx.declare("y", bv32)?;

// Assert that `x * y = 18`.
ctx.assert(ctx.eq(
    ctx.bvmul(x, y),
    ctx.binary(32, 18),
))?;

// And assert that neither `x` nor `y` is 1.
ctx.assert(ctx.not(ctx.eq(x, ctx.binary(32, 1))))?;
ctx.assert(ctx.not(ctx.eq(y, ctx.binary(32, 1))))?;

// Check whether the assertions are satisfiable. They should be in this example.
assert_eq!(ctx.check()?, Response::Sat);

// Print the solution!
let solution = ctx.get_value(vec![x, y])?;
for (variable, value) in solution {
    println!("{} = {}", ctx.display(variable), ctx.display(value));
}
// There are many solutions, but the one I get from Z3 is:
//
//     x = #x10000012
//     y = #x38000001
//
// Solvers are great at finding edge cases and surprising-to-humans results! In
// this case, I would have naively expected something like `x = 2, y = 9` or
// `x = 3, y = 6`, but the solver found a solution where the multiplication
// wraps around. Neat!
Ok(())

} ```

Debugging

Displaying S-Expressions

Want to display an S-Expression that you've built up to make sure it is what you expect? You can use the easy_smt::Context::display method:

```rust use easy_smt::ContextBuilder;

let ctx = ContextBuilder::new().build().unwrap();

let mysexpr = ctx.list(vec![ ctx.atom("hi"), ctx.atom("hello"), ctx.numeral(42), ]);

let string = format!("{}", ctx.display(mysexpr)); assert_eq!(string, "(hi hello 42)"); ```

Logging Solver Interactions

Need to debug exactly what is being sent to and received from the underlying solver? easy-smt uses the log crate and logs all communication with the solver at the TRACE log level.

For example, you can use env_logger to see the log messages. Initialize the logger at the start of main:

```rust fn main() { env_logger::init();

// ...

} ```

And then run your program with the RUST_LOG="easy_smt=trace" environment variable set to see the TRACE logs:

shell $ RUST_LOG="easy_smt=trace" cargo run --example sudoku [2023-01-09T23:41:05Z TRACE easy_smt::solver] -> (set-option :print-success true) [2023-01-09T23:41:05Z TRACE easy_smt::solver] <- success [2023-01-09T23:41:05Z TRACE easy_smt::solver] -> (set-option :produce-models true) [2023-01-09T23:41:05Z TRACE easy_smt::solver] <- success [2023-01-09T23:41:05Z TRACE easy_smt::solver] -> (set-option :produce-unsat-cores true) [2023-01-09T23:41:05Z TRACE easy_smt::solver] <- success [2023-01-09T23:41:05Z TRACE easy_smt::solver] -> (declare-fun cell_0_0 () Int) [2023-01-09T23:41:05Z TRACE easy_smt::solver] <- success [2023-01-09T23:41:05Z TRACE easy_smt::solver] -> (assert (and (> cell_0_0 0) (<= cell_0_0 9))) [2023-01-09T23:41:05Z TRACE easy_smt::solver] <- success [2023-01-09T23:41:05Z TRACE easy_smt::solver] -> (declare-fun cell_0_1 () Int) [2023-01-09T23:41:05Z TRACE easy_smt::solver] <- success [2023-01-09T23:41:05Z TRACE easy_smt::solver] -> (assert (and (> cell_0_1 0) (<= cell_0_1 9))) [2023-01-09T23:41:05Z TRACE easy_smt::solver] <- success ...

Replaying Solver Interactions

You can save all commands that are being sent to the solver to a file that you can replay without needing to dynamically rebuild your expressions, assertions, and commands.

```rust use easy_smt::ContextBuilder;

fn main() -> std::io::Result<()> { let ctx = ContextBuilder::new() // Everything needed to replay the solver session will be written // to replay.smt2. .replay_file(Some(std::fs::File::create("replay.smt2")?)) .solver("z3", ["-smt2", "-in"]) .build()?;

// ...

Ok(())

} ```

Inspiration

Inspired by the simple-smt haskell package.