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Functional heterogeneous list (hlist) library for Rust
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README.md

pl-hlist

Build Status Crates.io Docs.rs MIT licensed

This Rust library provides support for heterogeneous lists (known as HLists). An HList is a functional, tuple-like, strongly-typed data structure that can contain elements of differing types.

There are three layers in this library:

  • A basic HList data structure consisting of HCons and HNil types.
  • An hlist! macro for constructing an HList from a series of elements.
  • An HListSupport plugin/attribute that, when declared for a struct, allows for easy conversion of struct instances to/from an HList representation.

See the next section for more details on usage of these layers.

Usage

Add a dependency to your Cargo.toml:

[dependencies]
pl-hlist = "1.0"

Then, in your crate:

use pl_hlist::*;

An HList can be constructed manually as follows:

let x: HCons<u8, HCons<u32, HNil>> = HCons(1u8, HCons(666u32, HNil));

The hlist! macro provides a convenient shorthand for constructing an HList:

let x: HCons<u8, HCons<u32, HNil>> = hlist!(1u8, 666u32);

The custom HListSupport derive attribute can be applied to a struct declaration to automatically implement support for converting that struct to/from an HList representation:

#[derive(HListSupport)]
struct TestStruct {
    foo: u8,
    bar: u32
}

let hlist0 = hlist!(1u8, 666u32);
let s = TestStruct::from_hlist(hlist0);
assert_eq!(s.foo, 1u8);
assert_eq!(s.bar, 666u32);
let hlist1 = s.into_hlist();
assert_eq!(hlist0, hlist1);

License

pl-hlist is distributed under an MIT license. See LICENSE for more details.

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