evalrs

A Rust code snippet evaluator.

This tiny command evaluates Rust source code which read from the standard input stream.

It can handle extern crate declaration and has simple caching mechanism.

Documentation

Installation

Execute following command on your terminal:

```bash

Installs evalrs command

$ cargo install evalrs

Shows help message

$ evalrs -h ```

Usage Examples

evalrs command reads Rust code snippet from the standard input stream and evaluates it:

bash $ echo 'println!("Hello World!")' | evalrs Compiling evalrs_temp v0.0.0 (file:///tmp/evalrs_temp.daiPxHtjV2VR) Finished debug [unoptimized + debuginfo] target(s) in 0.51 secs Running `target\debug\evalrs_temp.exe` Hello World!

If target code includes extern crate declarations, the latest version of those crates will be downloaded and cached:

```bash

First time

$ echo 'extern crate numcpus; println!("{} CPUs", numcpus::get())' | evalrs Updating registry https://github.com/rust-lang/crates.io-index Compiling libc v0.2.18 Compiling numcpus v1.2.0 Compiling evalrstemp v0.0.0 (file:///tmp/evalrs_temp.HSRNyVQbM6s3) Finished debug [unoptimized + debuginfo] target(s) in 0.55 secs Running target\debug\evalrs_temp.exe 4 CPUs

Second time (cached crates are used)

$ echo 'extern crate numcpus; println!("{} CPUs", numcpus::get())' | evalrs Updating registry https://github.com/rust-lang/crates.io-index Compiling evalrstemp v0.0.0 (file:///tmp/evalrstemp.4QzdqRG5cY0x) Finished debug [unoptimized + debuginfo] target(s) in 0.24 secs Running target\debug\evalrs_temp.exe 4 CPUs ```

The command wraps input code snippet (except extern crate declarations) with a main function. But, if the code has a line which starts with "fn main()", it will be passed to rustc command without modification.

```bash

The first execution is equivalent to the second.

$ evalrs << EOS let a = 1; let b = 2; println!("a + b = {}", a + b); EOS Compiling evalrstemp v0.0.0 (file:///tmp/evalrstemp.gSXTXNaB6o8o) Finished debug [unoptimized + debuginfo] target(s) in 0.53 secs Running target/debug/evalrs_temp a + b = 3

$ evalrs << EOS fn main() { let a = 1; let b = 2; println!("a + b = {}", a + b); } EOS Compiling evalrstemp v0.0.0 (file:///tmp/evalrstemp.0kYvCRAj0TWI) Finished debug [unoptimized + debuginfo] target(s) in 0.20 secs Running target/debug/evalrs_temp a + b = 3 ```

Emacs Integration

As an example of integration with Emacs, you can use quickrun package to evaluate Rust code in a buffer by using evalrs command.

First, install quickrun package as follows:

lisp (require 'package) (add-to-list 'package-archives '("melpa" . "https://melpa.org/packages/") t) (package-initialize) (package-refresh-contents) (package-install 'quickrun)

Next, add a quickrun command to execute evalrs:

lisp (quickrun-add-command "evalrs" '((:command . "evalrs") (:exec . ("cat %s | %c %a"))) :default "evalrs")

Now, you can evaluate Rust code snippet in a buffer quickly:

```rust extern crate num_cpus;

println!("You have {} CPU cores", num_cpus::get());

// Type following to evaluate this buffer: // // M-x quickrun RET evalrs ```