Rusti

A REPL for the Rust programming language.

Rusti is a work in progress.

Building

Rusti builds with the latest Rust nightly, using the Cargo build system.
Currently, it must be built using a nightly release of the Rust compiler. Nightly releases can be found at the bottom of the Rust install page or installed using the --channel=nightly option to rustup.

Alternatively the nightly release can be used in the rusti directory tree using multirust and issuing the following command from rusti folder

multirust override nightly

Rusti requires GNU Readline.

Build with Cargo:

cargo build

Run tests:

cargo test

Run rusti:

cargo run

Cargo does not currently support an install subcommand, so if you would like to run rusti outside the build directory, you must manually copy target/rusti into a directory in your PATH environment variable.

Usage

Running rusti gives a prompt that accepts (most) any valid Rust code. If the final statement is an expression, the result will be displayed using the std::fmt::Debug trait. This is equivalent to println!("{:?}", expr);.

rusti=> println!("Hello, world!");
Hello, world!
rusti=> 2 + 2
4
rusti=> (0..5).collect::<Vec<_>>()
[0, 1, 2, 3, 4]

If any delimiters are left open, rusti will continue reading input until they are closed. Only then will the code be executed.

rusti=> fn factorial(n: u32) -> u32 {
rusti.>     match n {
rusti.>         0 => 0,
rusti.>         1 => 1,
rusti.>         n => n * factorial(n - 1),
rusti.>     }
rusti.> }
rusti=> factorial(3)
6
rusti=> factorial(4)
24
rusti=> factorial(5)
120

rusti can also run a file given on the command line.
Note that a rusti input file is not quite the same as a typical Rust program. A typical Rust program contains a function named main. While a rusti program can define functions, no functions will be called automatically. Instead, all statements not within a function body will be executed sequentially, just like interactive mode.

Loading Crates

Loading crates which are part of the standard Rust distribution is as easy as declaring the crate, thusly:

extern crate foo;

However, loading a crate that you have compiled yourself requires some extra steps:

• First, rusti must be able to find the location of compiled crate.
  You can add a path to its search list using the command line option -L path.
  rusti accepts any number of -L arguments.

• Secondly, rusti requires both an rlib and a dylib version of the compiled crate. If you're building your crate with Cargo, the following command will build the required files for your project's library:

  cargo rustc --lib -- --crate-type=rlib,dylib
  

  If you're building with rustc directly, simply add --crate-type=rlib,dylib to the build command to produce the required files.

Code completion

rusti provides optional support for code completion using Racer.

To enable code completion, install Racer as outlined in the Installation Instructions and place the racer executable into your PATH.

Commands

These are special inputs interpreted by rusti that are not directly evaluated as Rust code, though they may operate on Rust code.

Commands are invoked by entering a line beginning with . or :, followed by the name of the command and, perhaps, some text used by the command.

Command names may be arbitrarily abbreviated.
For example, .type may be abbreviated as .typ, .ty, or .t.

.block

The .block command will run multiple lines of Rust code as one program.

To end the command and run all code, input . on its own line.

rusti=> .block
rusti+> let a = 1;
rusti+> let b = a * 2;
rusti+> let c = b * 3;
rusti+> c
rusti+> .
6

Entering .q instead will end the command without running code.

.help

The .help command shows usage text for any available commands.

.load

The .load command evaluates the contents of a named file.

.print

The .print command will display the value of an expression, using the std::fmt::Display trait. This is equivalent to println!("{}", expr);.

.type

The .type command will display the type of an expression without running it.

rusti=> .type 42
42 = i32
rusti=> .t 'x'
'x' = char
rusti=> .t "Hello!"
"Hello!" = &'static str
rusti=> .t (1i32, 2u32)
(1i32, 2u32) = (i32, u32)
rusti=> fn foo() -> i32 { 1 }
rusti=> .t foo
foo = fn() -> i32 {foo}
rusti=> .t foo()
foo() = i32

Limitations

Currently, Rusti has the following limitations. I hope to fix each of them, but some may prove to be large problems to tackle.

• Functions and types are redefined in each round of input.
  This is inefficient.
• static items are also redefined in each round of input.
  This means that the address of a static item will change in every round of input and that the values of mut items or those with interior mutability will be reset to their initial definition on each round of input.
  This is bad.
• Use of thread_local! causes a crash.
  This is bad.
• let declarations are local to the input in which they are defined.
  They cannot be referenced later and are destroyed after that round of input completes its execution.
  This is inconvenient.
• And more!

License

Rusti is distributed under the terms of both the MIT license and the Apache License (Version 2.0).

See LICENSE-APACHE and LICENSE-MIT for details.