Crate reflect_nat

Expand description

Ready-made type-level values: Peano naturals, booleans, and heterogeneous lists, all implementing Reflect.

Where reify-reflect-core defines the Reflect trait and the RuntimeValue vocabulary, this crate provides the most useful concrete instances of that trait, the ones you reach for first when prototyping type-level code.

All of these types are zero-sized: they exist only at compile time and disappear at runtime. The Reflect impls are what give you a runtime handle on the value they encode.

§What’s in here

§Peano naturals

Z is zero, S<N> is “successor of N”.
Add, Mul, and Lt perform type-level arithmetic.
N0 through N8 are convenience aliases for the small numbers.
The Nat trait gives you a runtime u64 for any of these types, and the Reflect impl produces a RuntimeValue::Nat.

§Type-level booleans

True and False.
Not, And, Or perform compile-time boolean logic at the trait level.
Both reflect to a plain bool.

§Heterogeneous lists

HNil is the empty list, HCons<H, T> is a cons cell.
The HList trait exposes len() and is_empty() at the type level.
When every element implements Reflect<Value = RuntimeValue>, the whole HList reflects to a Vec<RuntimeValue>.

§Optional bridges (feature-gated)

frunk: interoperate with frunk’s HList.
typenum: bridge between Nat and typenum’s Unsigned.

§Examples

use reflect_nat::{Z, S, True, HNil, HCons};
use reify_reflect_core::{Reflect, RuntimeValue};

// Type-level natural: 3
type Three = S<S<S<Z>>>;
assert_eq!(Three::reflect(), RuntimeValue::Nat(3));

// Type-level boolean
assert_eq!(True::reflect(), true);

// Type-level HList: [3, 0]
type MyList = HCons<Three, HCons<Z, HNil>>;
assert_eq!(
    MyList::reflect(),
    vec![RuntimeValue::Nat(3), RuntimeValue::Nat(0)]
);

See also: reflect-derive for #[derive(Reflect)] on your own structs and enums (which can include the types from this crate as fields), and const-reify for going the other direction (runtime u64 to const generic).

Structs§

False: Type-level false.
HCons: A cons cell for heterogeneous lists. HCons<H, T> prepends head H to tail T.
HNil: The empty heterogeneous list.
S: Type-level successor. S<N> represents N + 1.
True: Type-level true.
Z: Type-level zero.

Traits§

Add: Type-level addition. Add<A, B> computes A + B.
And: Type-level boolean AND.
Bool: Marker trait for type-level booleans.
HList: Marker trait for type-level heterogeneous lists.
Lt: Type-level less-than comparison. Lt<A, B> is true when A < B.
Mul: Type-level multiplication. Mul<A, B> computes A * B.
Nat: Marker trait for types that represent type-level natural numbers.
Not: Type-level boolean NOT.
Or: Type-level boolean OR.

Type Aliases§

N0: Type alias for 0.
N1: Type alias for 1.
N2: Type alias for 2.
N3: Type alias for 3.
N4: Type alias for 4.
N5: Type alias for 5.
N6: Type alias for 6.
N7: Type alias for 7.
N8: Type alias for 8.