🦀 rust_eval

rust_eval is a lightweight Rust CLI tool that reads Rust source code interactively from standard input (stdin), validates it, dynamically compiles it using rustc, and executes it on the fly in an Eval-style workflow.

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Features

• Interactive Input: Stream Rust scripts directly from stdin until an EOF signal is received.
• Regex Validation & Implicit main Wrapping: Uses pre-compiled regex matching to verify the presence of a valid fn main entry point. If no main function or additional function definitions (fn ) are present, it automatically wraps the snippet inside an implicit main function.
• Cross-Platform Support: Automatically handles execution targets and temp paths for Unix (Linux/macOS) and Windows (.exe).
• Isolated Build Environment: Automatically manages a temporary directory (tmp/) for source generation and compilation, ensuring thorough cleanup even on error.
• Detailed Execution Output: Displays structured reports for STDOUT, STDERR, and the process Exit Code.

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How It Works

1. Input Reading: Displays a >>> prompt and streams user code until EOF (Ctrl+D on Unix/macOS, Ctrl+Z on Windows) is signaled.
2. Validation & Wrapping: Evaluates input against a LazyLock<Regex> pattern. If a valid fn main(...) signature exists, it uses the input as-is. If no main exists and no other functions are defined, it automatically wraps the input inside fn main() { ... }. If other functions exist without a main, it returns an error.
3. Source Preparation: Creates the tmp/ workspace and outputs tmp/tmp.rs, wrapped with auto-generated headers and footers.
4. Compilation & Execution: Invokes rustc tmp/tmp.rs --out-dir tmp. On successful compilation, executes the generated binary (tmp/tmp or tmp/tmp.exe), passing stdin, stdout, and stderr directly through to the terminal process.
5. Cleanup: Cleans up the temporary workspace upon successful execution or runtime failures.

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Getting Started

Prerequisites

• Rust toolchain installed with rustc available in your system PATH.

Running locally

1. Clone the repository:

   git clone https://github.com/Jacob-Dayan/rust-eval.git
   cd rust_eval

2. Run using cargo:

   cargo run

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Example Usage

Upon starting the binary:

To enter, stream EOF (ctrl+D on Unix, ctrl+Z on Windows)

>>> fn main() {
    let numbers = vec![1, 2, 3, 4, 5];
    let sum: i32 = numbers.iter().sum();
    println!("The sum is: {}", sum);
}

Press Ctrl+D (or Ctrl+Z on Windows) to trigger evaluation:

The sum is: 15

And if you just wanna run a simple code snippet, you don't even have to mess with a main function.

The code below works exactly the same as the one above:

To enter, stream EOF (ctrl+D on Unix, ctrl+Z on Windows)

>>> let numbers = vec![1, 2, 3, 4, 5];
    let sum: i32 = numbers.iter().sum();
    println!("The sum is: {}", sum);

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Project Structure

.
├── src/
│   ├── lib.rs      # Exported macros and modules
│   ├── consts.rs   # Path constants, Regex matchers, Header & Footer wrappers
│   └── main.rs     # CLI entry point, input handling, process control, and cleanup
└── Cargo.toml

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License

This project is licensed under the MIT License.