evalrs

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:

# 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:

$ 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:

# First time
$ echo 'extern crate num_cpus; println!("{} CPUs", num_cpus::get())' | evalrs
    Updating registry `https://github.com/rust-lang/crates.io-index`
   Compiling libc v0.2.18
   Compiling num_cpus v1.2.0
   Compiling evalrs_temp 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 num_cpus; println!("{} CPUs", num_cpus::get())' | evalrs
    Updating registry `https://github.com/rust-lang/crates.io-index`
   Compiling evalrs_temp v0.0.0 (file:///tmp/evalrs_temp.4QzdqRG5cY0x)
    Finished debug [unoptimized + debuginfo] target(s) in 0.24 secs
     Running `target\debug\evalrs_temp.exe`
4 CPUs

If you want to use a specific version of an external crate, you will be able to specify it at a trailing comment of the extern crate declaration.

$ evalrs << EOS
extern crate num_cpus; // "1.2.0"
extern crate some_local_crate; // {path = "/path/to/some_local_crate"}
extern crate other_crate; // other-crate = "1"

println!("{} CPUs", num_cpus::get());
EOS

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.

# The first execution is equivalent to the second.
$ evalrs << EOS
let a = 1;
let b = 2;
println!("a + b = {}", a + b);
EOS
   Compiling evalrs_temp v0.0.0 (file:///tmp/evalrs_temp.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 evalrs_temp v0.0.0 (file:///tmp/evalrs_temp.0kYvCRAj0TWI)
    Finished debug [unoptimized + debuginfo] target(s) in 0.20 secs
     Running `target/debug/evalrs_temp`
a + b = 3

To support documentation test format, evalrs removes "# " string at the beginning of a line.

$ evalrs << EOS
# fn main() {
let a = 1;
let b = 2;
println!("a + b = {}", a + b);
# }
EOS
   Compiling evalrs_temp v0.0.0 (file:///tmp/evalrs_temp.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:

(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:

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

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

extern crate num_cpus;

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

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