lamcal 0.2.0

A lambda calculus parser and interpreter
Documentation

Lamcal

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lamcal is a Lambda Calculus parser and evaluator written in Rust.

It 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))
  • 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 mutate the term in place and a standalone function, e.g. reduce, that leave the original term unchanged and return 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:

[dependencies]
lamcal = "0.2"

and this to your crate root:

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:

[dependencies]
lamcal = { version = "0.2", 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.