pry-rs

An interactive REPL breakpoint for Rust, inspired by Ruby's binding.pry.

Drop a pry!() into your code and execution pauses with an interactive prompt where you can inspect variables, view the surrounding source, and print a backtrace — then continue running.

The prompt supports line editing and history (arrow keys, Ctrl-A/E/H, etc.) via rustyline. The only dependency is rustyline, and even that can be disabled with default-features = false for a std-only build.

Why not exactly like binding.pry?

Ruby is fully dynamic, so binding.pry can see every local variable automatically. Rust is compiled and has no runtime reflection, so you tell pry! which variables (or expressions) to capture. Anything that implements Debug works.

Installation

[dependencies]
pry-rs = { git = "https://github.com/100010/pry-rs" }

Usage

use pry::pry;

#[derive(Debug)]
struct User {
    name: String,
    age: u32,
}

fn main() {
    let user = User { name: "alice".into(), age: 30 };
    let scores = [88, 92, 75];

    pry!(user, scores, scores.len()); // ← execution pauses here

    println!("resumed!");
}

Running this opens a prompt:

From: src/main.rs:13
    ...
 => 13:     pry!(user, scores, scores.len());
    ...
Type "help" for commands, "continue" to resume.
pry> ls
user User = User { name: "alice", age: 30 }
scores [i32; 3] = [88, 92, 75]
scores.len() usize = 3
pry> p user
=> (User) User {
    name: "alice",
    age: 30,
}
pry> user.name
=> "alice"
pry> scores[1]
=> 92
pry> c
resumed!

Commands

Notes

• Values are captured (as Debug output) at the moment pry! runs; the REPL shows a snapshot, it cannot mutate your program's state.
• Sub-field access (user.name, items[0]) works by parsing the captured Debug text. Output from #[derive(Debug)] parses reliably; exotic hand-written Debug impls may not.
• For full backtraces, run with RUST_BACKTRACE=1.
• Colors are disabled automatically when stdout is not a terminal or when NO_COLOR is set.
• Requires Rust 1.76+ (std::any::type_name_of_val).

Try the example

cargo run --example basic

License

MIT