# Lamcal REPL
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[license]: LICENSE
[lamcal]: https://github.com/haraldmaida/lamcal
[lamcal-repl]: .
[lamcal-repl] is a [Lambda Calculus] REPL command line application written in [Rust]. It can be used
to play around with lambda calculus expressions interactively.
This application is inspired by this [talk](https://www.youtube.com/watch?v=3VQ382QG-y4) by [glebec]
where he plays around with lambda calculus in a JavaScript console.
[lamcal-repl] uses the [lamcal] library crate for the lambda calculus functionality and adds
the REPL things to make it an application. The name of the executable is `lamcali`.
## Installation
To install the [lamcal-repl] command line application run the following commands in your terminal:
```
> cargo install lamcal-repl
```
After it has been installed successfully we can run [lamcal-repl] by typing the name of the
executable:
```
> lamcali
```
Alternatively we can clone this git repository, go to the `repl` subdirectory and type `cargo run`,
like so
```
> cd lamcal/repl
lamcal/repl> cargo run
```
## Usage
When the application starts we see the following in the command line:
```
info: Welcome to lamcal-repl, the Lambda Calculus Repl, version 0.1.0
λ>
```
Notice that the command line prompt changes to `λ>`. To evaluate a lambda expression we simple type
in the expression at the prompt, like so:
```
λ> (\x.(\y.x y) a) b
```
After pressing enter, the expression gets parsed and the default α-conversion and β-reduction is
applied. The result is printed to the console, like so:
```
λ> (\x.(\y.x y) a) b
b a
```
We can use the backslash character \ or the greek lowercase lambda λ to denote a lambda abstraction
with a lambda expressions. The parser understands both backslash as well as the lowercase lambda
symbol as the start of an abstraction.
The repl support commands to control the behavior of the application. Commands always start with a
colon. Most important commands are:
* `:h` or `:help` to print out help information
* `:q` or `:quit` to quit the application
A list of all implemented commands is given in the help information (command `:h`).
## License
Licensed under Apache License, Version 2.0<br/>
see [LICENSE] or http://www.apache.org/licenses/LICENSE-2.0 for details.
### Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
licensed as above, without any additional terms or conditions.
--------------------------------------------------------------------------------
[de bruijn index]: https://en.wikipedia.org/wiki/De_Bruijn_index
[krivine machine]: https://en.wikipedia.org/wiki/Krivine_machine
[lambda calculus]: https://en.wikipedia.org/wiki/Lambda_calculus
[lcss]: https://www.youtube.com/watch?v=GYCYq0lEFhE
[rust]: https://www.rust-lang.org
[SECD machine]: https://en.wikipedia.org/wiki/SECD_machine
[glebec]: https://github.com/glebec