TYP: type-level programming in Rust

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TYP enables you to write type operators, the functions that translates types, in Rust syntax.

It is re-design of willcrichton/Tyrade and was inspired by jerry73204/type-freak.

Features

Rusty syntax

TYP adopts Rust-like syntax, where values become types, and types become trait bounds. The core concept is the type operator, which is a function that takes type arguments and produce types. Trait bounds are optionally added to input and output types.

fn TypeOperatorName<generic1, generic2>(type1: _, type2: Trait1 + Trait2) -> TraitBound { ... }

• <generic1, generic2> lists the generic identifiers that helps disginguishing from public types.

• type1 and type2 are input types composed of generics and public types.

• type1: _ means the type has no trait bound.

• The output trait bound fn() -> TraitBound is optional.

The snipplet demonstrates a simple type operator.

typ! {
    use typenum::Unsigned;

    fn Add<lhs, rhs>(lhs: Unsigned, rhs: Unsigned) -> Unsigned {
        lhs + rhs
    }
}

Built-in typenum support

TYP provides first-class support to typenum. Integer literals are translated to typenum types. The following literals are understood by TYP.

• Signed integers: 7 or 7i
• Unsigned integers: 7u
• Bits: true and false

Common binary and unary operators applies on types with appropriate traits. For example, A + B expands to <A as Add<B>>::Output.

typ! {
    use typenum::{Integer, Bit};

    fn IsOdd<value>(value: Integer) -> Bit {
        if value % 2 == 1 {
            true
        } else {
            false
        }
    }
}

Type matching

Like normal Rust, the match syntax lets you match and unpack types. You can bind new generics on a pattern using #[generics(...)] attribute.

The example demonstrates a type operator that appends a type at the end of type-level list. It's done by recursively unpack the list into Cons nodes and Nil end-of-list marker.

pub trait List {}

pub struct Cons<Head, Tail: List> { /* omit */ }
impl<Head, Tail: List> List for Cons<Head, Tail> {}

pub struct Nil;
impl List for Nil {}

typ! {
    fn Append<input, value>(input: List, value: _) -> List {
        match input {
            #[generics(head, tail: List)]
            Cons::<head, tail> => {
                let new_tail = Append(tail, value);
                Cons::<head, new_tail>
            }
            Nil => {
                Cons::<value, Nil>
            }
        }
    }
}

Examples

More advanced examples can be found in tests/ directory.

• if/else
• match
• binary GCD

License

MIT license. See LICENSE.txt.