https://github.com/lucasem/polytype-rs

A Hindley-Milner polymorphic typing system
https://github.com/lucasem/polytype-rs

hindley-milner polymorphism type-inference types

Last synced: 2 months ago
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A Hindley-Milner polymorphic typing system

• Host: GitHub
• URL: https://github.com/lucasem/polytype-rs
• Owner: lorepozo
• License: mit
• Created: 2018-02-15T00:59:06.000Z (over 6 years ago)
• Default Branch: main
• Last Pushed: 2023-12-18T13:36:02.000Z (11 months ago)
• Last Synced: 2024-05-22T21:34:43.999Z (6 months ago)
• Topics: hindley-milner, polymorphism, type-inference, types
• Language: Rust
• Homepage: https://docs.rs/polytype
• Size: 224 KB
• Stars: 46
• Watchers: 5
• Forks: 8
• Open Issues: 3
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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• awesome-rust-formalized-reasoning - polytype - Hindley-Milner polymorphic typing system. (Projects / Libraries)

README

        
# polytype

[![CI](https://github.com/lorepozo/polytype-rs/actions/workflows/ci.yaml/badge.svg)](https://github.com/lorepozo/polytype-rs/actions/workflows/ci.yaml)

[![crates.io](https://img.shields.io/crates/v/polytype.svg)](https://crates.io/crates/polytype)

[![docs.rs](https://docs.rs/polytype/badge.svg)](https://docs.rs/polytype)

A [Hindley-Milner](https://wikipedia.org/wiki/Hindley–Milner_type_system) polymorphic typing system.

Implements type inference via unification.

## Usage

```toml

[dependencies]

polytype = "7.0"

```

**`polytype`** provides the

[`TypeScheme`](https://docs.rs/polytype/~7/polytype/enum.TypeScheme.html) and

[`Type`](https://docs.rs/polytype/~7/polytype/enum.Type.html) enums, the

[`Context`](https://docs.rs/polytype/~7/polytype/struct.Context.html)

struct, and the

[`tp!`](https://docs.rs/polytype/~7/polytype/macro.tp.html) and

[`ptp!`](https://docs.rs/polytype/~7/polytype/macro.ptp.html) macros which

help to concisely create types and type schemes.

Unification:

```rust

let mut ctx = Context::default();

// t1: list(int → α) ; t2: list(β → bool)

let t1 = tp!(list(tp!(@arrow[tp!(int), tp!(0)])));

let t2 = tp!(list(tp!(@arrow[tp!(1), tp!(bool)])));

ctx.unify(&t1, &t2).expect("unifies");

let t1 = t1.apply(&ctx);

let t2 = t2.apply(&ctx);

assert_eq!(t1, t2); // list(int → bool)

```

Apply a type context:

```rust

let mut ctx = Context::default();

// assign t0 to int

ctx.extend(0, tp!(int));

let t = tp!(list(tp!(0)));

assert_eq!(t.to_string(), "list(t0)");

let t = t.apply(&ctx);

assert_eq!(t.to_string(), "list(int)");

```

Instantiate a `TypeScheme`:

```rust

let mut ctx = Context::default();

// ∀α. list(α)

let scheme = ptp!(3; tp!(list(tp!(3))));

// They instantiate to new fresh type variables

let t1 = scheme.instantiate(&mut ctx);

let t2 = scheme.instantiate(&mut ctx);

assert_eq!(t1.to_string(), "list(t0)");

assert_eq!(t2.to_string(), "list(t1)");

```

See the [documentation](https://docs.rs/polytype) for more details.

## Features

By default `polytype` includes a type parser that can be invoked with

[str::parse](https://doc.rust-lang.org/stable/std/primitive.str.html#method.parse).

This can be disabled with `default-features = false`.