https://github.com/jzbor/lash

Simple REPL shell for untyped lambda expressions.
https://github.com/jzbor/lash

Last synced: 1 day ago
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Simple REPL shell for untyped lambda expressions.

• Host: GitHub
• URL: https://github.com/jzbor/lash
• Owner: jzbor
• License: mit
• Created: 2022-09-12T12:38:00.000Z (about 2 years ago)
• Default Branch: master
• Last Pushed: 2024-10-24T21:59:43.000Z (23 days ago)
• Last Synced: 2024-10-26T09:35:43.802Z (22 days ago)
• Language: Rust
• Homepage: https://jzbor.de/lash/
• Size: 138 KB
• Stars: 5
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

Awesome Lists containing this project

• awesome-rust-formalized-reasoning - Lambda Shell - simple REPL shell for untyped lambda expressions. (Lambda Calculus / Libraries)

README

        
# Lambda Shell

This is a simple REPL shell for [untyped lambda expressions](https://en.wikipedia.org/wiki/Lambda_calculus).

I wrote it mostly for playing around a little bit with the lambda calculus.

Some parts of it are wildly inefficient, but it is fine for education purposes.

The shell can evaluate lambda expressions, assignments and macros.

# Example

There are builtin terms `SUCC` and `NIL` to create natural numbers using church numerals:

```

[λ] @usestd

@usestd

[λ] one := SUCC NIL

one := SUCC NIL

[λ] two := SUCC (SUCC NIL)

two := SUCC (SUCC NIL)

[λ] !normalize (ADD one two)

\f . \x . f (f (f x))

```

You can select different reduction strategies at runtime:

```

[λ] @usestd

@usestd

[λ] !vnormalize (AND TRUE FALSE)

AND TRUE FALSE

(\q . TRUE q TRUE) FALSE

(\q . (\y . q) TRUE) FALSE

(\q . q) FALSE

FALSE

[λ] @set strategy normal

@set strategy normal

[λ] !vnormalize (AND TRUE FALSE)

AND TRUE FALSE

(\q . TRUE q TRUE) FALSE

TRUE FALSE TRUE

(\y . FALSE) TRUE

FALSE

```

## Features

* normal (leftmost-outermost) and applicative (leftmost-innermost) reduction strategies

* capture-avoiding substitution

* simple constructs provided via builtins

* macros for processing lambda terms

## Installation

[You can find more information about installation and building from source here.](https://jzbor.de/lash/installation.html)