An untyped lambda calculus interpreter.

It has several useful features:

- Has support for the usual implicit parenthesization rules of lambda calculus

    - See the documentation for the `parse` function [on here](https://docs.rs/lambda_calc)).

- Highlights the expression reduced last at each beta reduction step

    - (Can be disabled.)

- Allows bind lambda terms to symbols (definitions)

    - Lazy symbol substitution

    - Allows recursive definitions

- Has context-sensitive TAB completion, matching brace highlighter, and history support
(thanks to [rustyline](https://crates.io/crates/rustyline)).

- Allows escaping line breaks with `&`

    - The line will be saved to history as a single line.

- Has a non-interactive mode whose output is in a can be easily parsed by scripts

- Allows counting the number of reduction steps

...along with many other features; run with `--help` for more.

## Screenshots

![Screenshot 1](screenshots/combinators.png)

![Screenshot 2](screenshots/load_add.png)

![Screenshot 3](screenshots/count_nostep.png)

![Screenshot 4](screenshots/non_interactive.png)

## Installation

[Install cargo](https://doc.rust-lang.org/cargo/getting-started/installation.html)
if you don't have it, then run

```
$ cargo install lambda_calc
```

This will install the `lambda_calc` binary.
Opitonally, you may use the `--root` option to install to a different directory;
run `man cargo-install` for details.