Lamcal

[lamcal] is a [Lambda Calculus] parser and evaluator written in [Rust]. It implements a pure untyped lambda calculus.

The library can be used to

• parse lambda expressions in classic notation into terms, like parse_str("(λx.(λy.x y) a) b")
  or parse_str("(\\x.(\\y.x y) a) b")
• construct terms programmatically using functions, e.g. lam("x", app(var("x"), var("y")))
• construct a sequence of function applications using the macro app!, e.g. app![var("a"), var("b"), var("c")] which is equivalent to app(app(var("a"), var("b")), var("c))
• evaluate lambda terms to replace variables with predefined terms bound to the variable's name in the environment
• apply α-conversion to terms using different strategies, such as enumeration or appending the tick symbol
• apply β-reduction to terms using different strategies, such as call-by-name, normal-order or call-by-value
• be extended by implementing user specific strategies for α-conversion and β-reduction.

The separate crate [lamcal-repl] provides a command line REPL (read-evaluate-print-loop) application to play around with lambda calculus terms and applying α-conversion and β-reduction interactively.

Features:

• Evaluation functions are provided in two variants: An associated function, e.g. Term::reduce, that mutates the term in place and a standalone function, e.g. reduce, that leaves the original term unchanged and returns the result as a new term.
• Strategies for α-conversion and β-reduction are defined as traits to easily implement custom strategies and use it with the functionality of this library.
• The parser gives detailed information about parse errors, like the position of the error in the source stream and what would have been expected instead in a valid expression.
• Optional support for [failure] crate compatible error types.

Usage

To use [lamcal] as a library in your project add this to your Cargo.toml file:

toml [dependencies] lamcal = "0.3"

and this to your crate root:

rust extern crate lamcal;

For details about the library see the [documentation] at crates.io.

This library optionally supports the [failure] crate. The support for the failure crate is a crate feature. To enable it add the dependency to your Cargo.toml like so:

toml [dependencies] lamcal = { version = "0.3", features = ["failure"] }

License

Licensed under Apache License, Version 2.0
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.