1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443
#![forbid(unsafe_code)]
#![no_std]
#![cfg_attr(feature = "doc", feature(doc_auto_cfg))]
#![doc = include_str!("../README.md")]
#[cfg(feature = "typenum")]
mod typenum_ext;
mod sealed {
pub trait Sealed {}
}
use sealed::Sealed;
#[cfg(feature = "typenum")]
use typenum_ext::UnsignedExt;
use core::marker::PhantomData;
#[doc(hidden)]
pub trait TListImpl {
type Last<X>;
type Inits<X>: TList;
}
/// Type-level lists.
///
/// This trait is a "type-level enum".
/// [trait@TList], [TNil] and [TCons] are the type-level equivalent of the following value-level enum:
///
/// ```ignore
/// pub enum List<H, T> {
/// Nil,
/// Cons(H, T),
/// }
/// ```
///
/// This trait can be considered a 'marker' trait:
/// It has no methods to be called at runtime.
/// It only has some GATs.
///
/// Rather than calling these GATs directly,
/// it is recommended to instead use their type aliases,
/// as calling those is less verbose:
///
/// ```rust
/// use tlist::*;
///
/// // This is possible...
/// type Fine = <TList![u8, u16] as TList>::Concat<TList![u32, u64]>;
///
/// // But this is more readable:
/// type Nice = Concat<TList![u8, u16], TList![u32, u64]>;
///
/// static_assertions::assert_type_eq_all!(Fine, Nice);
/// ```
pub trait TList: Sealed + TListImpl {
/// Implementation of [type@Concat].
type Concat<Rhs: TList>: TList;
/// Implementation of [type@Reverse].
type Reverse: TList;
/// True iff the list is empty, false otherwise.
///
/// Returns a bool as associated const value.
/// If you'd rather use a type, see [IsEmpty]
/// (which needs `typenum` feature to be enabled)
///
/// Also see the [Empty] and [NonEmpty] traits.
const IS_EMPTY: bool;
/// The amount of elements in the list.
///
/// Returns an usize as associated const value.
/// If you'd rather use a type, see [Len]
/// (which needs `typenum` feature to be enabled)
const LEN: usize;
/// Implementation of [type@IsEmpty].
#[cfg(feature = "typenum")]
type IsEmpty: Bit;
/// Implementation of [type@Len].
#[cfg(feature = "typenum")]
type Len: UnsignedExt;
}
/// The empty [trait@TList].
///
/// Only [TNil] implements this constraining trait.
///
/// See also [TList::IS_EMPTY] and [IsEmpty] if you want work with both [Empty] and [NonEmpty]
/// lists generically.
pub trait Empty: TList + Sealed {}
/// Non-empty [trait@TList]s.
///
/// Any [trait@TList] except [TNil] implements this constraining trait.
/// (In other words: Any [`TCons<H, T>`], regardless of what `H` or `T` it contains, implements it.)
///
/// Quite a number of operations are only defined for non-empty [trait@TList]s,
/// so this constraint is used a lot in the library itself as well.
///
/// See also [TList::IS_EMPTY] and [IsEmpty] if you want work with both [Empty] and [NonEmpty]
/// lists generically.
pub trait NonEmpty: TList + Sealed {
/// Implementation of [type@First].
type First;
/// Implementation of [type@Rest].
type Rest: TList;
/// Implementation of [type@Last].
type Last;
/// Implementation of [type@Inits].
type Inits: TList;
}
/// The empty TList.
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Default)]
pub struct TNil;
/// A non-empty TList whose first element is `H` and whose tail is the TList `T`.
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Default)]
pub struct TCons<H, T: TList>(PhantomData<(H, T)>);
impl Sealed for TNil {}
impl<H, T: TList> Sealed for TCons<H, T> {}
impl TListImpl for TNil {
type Last<X> = X;
type Inits<X> = TNil;
}
impl TList for TNil {
type Concat<Rhs: TList> = Rhs;
type Reverse = TNil;
#[cfg(feature = "typenum")]
type IsEmpty = B1;
#[cfg(feature = "typenum")]
type Len = U0;
const IS_EMPTY: bool = true;
const LEN: usize = 0;
}
impl Empty for TNil {}
impl<H, T: TList> TListImpl for TCons<H, T> {
type Last<X> = T::Last<H>;
type Inits<X> = TCons<X, T::Inits<H>>;
}
impl<H, T: TList> TList for TCons<H, T> {
type Concat<Rhs: TList> = TCons<H, T::Concat<Rhs>>;
type Reverse = Concat<T::Reverse, TCons<H, TNil>>;
#[cfg(feature = "typenum")]
type IsEmpty = B0;
#[cfg(feature = "typenum")]
type Len = <T::Len as UnsignedExt>::Succ;
const IS_EMPTY: bool = false;
const LEN: usize = {
T::LEN + 1
};
}
impl<H, T: TList> NonEmpty for TCons<H, T> {
type First = H;
type Rest = T;
type Last = T::Last<H>;
type Inits = T::Inits<H>;
}
/// Shorthand macro to construct TList types.
///
/// This is usually much more readable than writing out the nesting of
/// [TCons] and [TNil] by hand.
///
/// ```rust
/// use tlist::*;
///
/// use static_assertions::assert_type_eq_all as type_eq;
/// use typenum::consts::{U1, U2, U3, U4, U42};
///
/// type_eq!(TList![], TNil);
///
/// type_eq!(TList![U42], TCons<U42, TNil>);
///
/// type_eq!(TList![U1, U2, U3], TCons<U1, TCons<U2, TCons<U3, TNil>>>);
///
/// // You can also use `...Rest` for the last argument:
/// type Rest = TList![U3, U4];
/// type_eq!(TList![U1, U2, ...Rest], TCons<U1, TCons<U2, Rest>>);
/// ```
#[macro_export]
// Implementation based on the frunk crate's HList! macro.
macro_rules! TList {
() => { $crate::TNil };
(...$Rest:ty) => { $Rest };
($A:ty) => { $crate::TList![$A,] };
($A:ty, $($tok:tt)*) => {
$crate::TCons<$A, $crate::TList![$($tok)*]>
};
}
/// Type-level 'function' to return the first element of a TList
///
/// Only implemented for non-empty TLists.
///
/// ```rust
/// use tlist::*;
/// use typenum::consts::{U1, U2, U3};
/// use static_assertions::assert_type_eq_all as assert_type_eq;
///
/// assert_type_eq!(First<TList![U1, U2, U3]>, U1);
///
/// assert_type_eq!(First<TList![i8, usize, i32, u64]>, i8);
/// ```
pub type First<List> = <List as NonEmpty>::First;
/// Type-level 'function' to return the first element of a TList
///
/// Only implemented for non-empty TLists.
///
/// ```rust
/// use tlist::*;
/// use typenum::consts::{U1, U2, U3};
/// use static_assertions::assert_type_eq_all as assert_type_eq;
///
/// assert_type_eq!(Rest<TList![U1, U2, U3]>, TList![U2, U3]);
///
/// assert_type_eq!(Rest<TList![i8, usize, i32, u64]>, TList![usize, i32, u64]);
/// ```
pub type Rest<List> = <List as NonEmpty>::Rest;
/// Type-level 'function' to return the all elements but the last element of a TList
///
/// Only implemented for non-empty TLists.
/// ```rust
/// use tlist::*;
/// use typenum::consts::{U1, U2, U3};
/// use static_assertions::assert_type_eq_all as assert_type_eq;
///
/// assert_type_eq!(Last<TList![U1, U2, U3]>, U3);
///
/// assert_type_eq!(Last<TList![i8, usize, i32, u64]>, u64);
/// ```
pub type Last<List> = <List as NonEmpty>::Last;
/// Type-level 'function' to return the all elements but the last element of a TList
///
/// Only implemented for non-empty TLists.
/// ```rust
/// use tlist::*;
/// use typenum::consts::{U1, U2, U3};
/// use static_assertions::assert_type_eq_all as assert_type_eq;
///
/// assert_type_eq!(Inits<TList![U1, U2, U3]>, TList![U1, U2]);
///
/// assert_type_eq!(Inits<TList![i8, usize, i32, u64]>, TList![i8, usize, i32]);
/// ```
pub type Inits<List> = <List as NonEmpty>::Inits;
/// Type-level 'function' to concatenate two TLists.
///
///
/// ```rust
/// use tlist::*;
/// use typenum::consts::{U1, U2, U3, U4, U5};
/// use static_assertions::assert_type_eq_all as assert_type_eq;
///
/// assert_type_eq!(Concat<TList![], TList![]>, TList![]);
///
/// assert_type_eq!(Concat<TList![U1], TList![]>, TList![U1]);
///
/// assert_type_eq!(Concat<TList![U2], TList![]>, TList![U2]);
///
/// assert_type_eq!(Concat<TList![U1, U2], TList![U3, U4, U5]>, TList![U1, U2, U3, U4, U5]);
/// ```
///
pub type Concat<Lhs, Rhs> = <Lhs as TList>::Concat<Rhs>;
/// Type-level 'function' to reverse a TList.
///
/// ```rust
/// use tlist::*;
/// use typenum::consts::{U1, U2, U3, U4, U5};
/// use static_assertions::assert_type_eq_all as assert_type_eq;
///
/// assert_type_eq!(Reverse<TList![]>, TList![]);
///
/// assert_type_eq!(Reverse<TList![U3, U2, U1]>, TList![U1, U2, U3]);
/// ```
///
pub type Reverse<List> = <List as TList>::Reverse;
#[cfg(feature = "typenum")]
use typenum::{Bit, B0, B1, consts::U0};
/// Type-level 'function' to calculate the length of a TList.
///
/// You can turn the result into a `usize` using `Len<List>::USIZE` or `Len<List>::to_usize()`.
///
/// (See [`typenum::Unsigned`].)
#[cfg(feature = "typenum")]
pub type Len<List> = <List as TList>::Len;
/// Type-level 'function' returning [`typenum::B1`] when the list is empty; [`typenum::B0`] otherwise.
///
/// You can turn the result into a `bool` using `IsEmpty<List>::BOOL` or `IsEmpty<List>::to_bool()`.
///
/// (See [`typenum::Bit`] for more on this.)
/// ```rust
/// use tlist::*;
/// use typenum::{B0, B1, Bit};
/// use static_assertions::assert_type_eq_all as assert_type_eq;
///
/// assert_type_eq!(IsEmpty<TList![]>, B1);
/// assert_type_eq!(IsEmpty<TList![i32]>, B0);
/// assert_type_eq!(IsEmpty<TList![u32, i64]>, B0);
///
/// assert_eq!(IsEmpty::<TList![]>::BOOL, true);
/// assert_eq!(IsEmpty::<TList![&'static str]>::BOOL, false);
/// ```
///
/// [IsEmpty] is a type-level function that works for any [trait@TList], returning a type-level boolean.
/// If you want to _constrain_ what kind of [trait@TList] is allowed for a certain operation,
/// use the [Empty] or [NonEmpty] constraining traits.
#[cfg(feature = "typenum")]
pub type IsEmpty<List> = <List as TList>::IsEmpty;
/// Constraint which only holds if a TList is a prefix of `Other`.
///
/// This is not a type-level 'function', but rather a constraint you can use to make compiler errors more readable.
///
/// Since this is a constraint, and only holds for a small subset of [trait@TList]s, it _is_
/// implemented as a separate trait and not as a GAT.
///
/// ```rust
/// use tlist::*;
/// use typenum::consts::{U1, U2, U3, U4, U42};
///
/// static_assertions::assert_impl_all!(TList![U1, U2]: Prefix<TList![U1, U2, U3, U4]>);
/// static_assertions::assert_not_impl_any!(TList![U42]: Prefix<TList![U1, U2, U3, U4]>);
/// ```
///
/// Also see [EitherPrefix].
pub trait Prefix<Other: TList> {}
// prefix [] _ = true
impl<Other: TList> Prefix<Other> for TNil {}
// prefix (h : ls) (h : rs) == prefix ls rs
impl<H, Ls: TList, Rs: TList> Prefix<TCons<H, Rs>> for TCons<H, Ls> where Ls: Prefix<Rs> {}
/// Constraint which either holds if a [trait@TList] is a prefix of `Other` or if `Other` is a prefix of this [trait@TList].
///
/// Relaxed variant of [Prefix].
///
/// ```rust
/// use tlist::*;
/// use typenum::consts::{U1, U2, U3, U4, U42};
///
/// static_assertions::assert_impl_all!(TList![U1, U2]: EitherPrefix<TList![U1, U2, U3, U4]>);
/// static_assertions::assert_impl_all!(TList![U1, U2, U3, U4]: EitherPrefix<TList![U1, U2]>);
/// static_assertions::assert_not_impl_any!(TList![U42]: EitherPrefix<TList![U1, U2, U3, U4]>);
/// static_assertions::assert_not_impl_any!(TList![U1, U2, U3, U4]: EitherPrefix<TList![U4, U3, U2, U1]>);
/// ```
pub trait EitherPrefix<Other: TList> {}
// eitherPrefix [] [] == true
impl EitherPrefix<TNil> for TNil {}
// eitherPrefix [] (f : gs) == true
impl<F, GS: TList> EitherPrefix<TCons<F, GS>> for TNil {}
// eitherPrefix (f : fs) [] == true
impl<F, FS: TList> EitherPrefix<TNil> for TCons<F, FS> {}
// eitherPrefix (f : fs) (g : gs) == true
impl<F, FS: TList, GS: TList> EitherPrefix<TCons<F, GS>> for TCons<F, FS> where FS: EitherPrefix<GS> {}
#[cfg(test)]
pub mod tests {
// Since all of this is type-level code,
// these tests run at compile-time :-).
use super::*;
use static_assertions::assert_type_eq_all as assert_type_eq;
use typenum::consts::*;
#[test]
fn first() {
assert_type_eq!(U1, First<TList![U1, U2]>);
}
#[test]
fn rest() {
assert_type_eq!(TList![U2], Rest<TList![U1, U2]>);
}
#[test]
fn last() {
assert_type_eq!(U2, Last<TList![U1, U2]>);
assert_type_eq!(U1, Last<TList![U1]>);
}
#[test]
fn inits() {
assert_type_eq!(TList![U1, U2], Inits<TList![U1, U2, U3]>);
assert_type_eq!(TList![], Inits<TList![U10]>);
}
#[test]
fn concat() {
assert_type_eq!(TList![U1, U2, U3], Concat<TList![U1], TList![U2, U3]>);
}
#[test]
fn reverse() {
assert_type_eq!(TCons<U3, TCons<U2, TCons<U1, TNil>>>, Reverse<TCons<U1, TCons<U2, TCons<U3, TNil>>>>);
}
}
#[cfg(test)]
#[cfg(feature = "typenum")]
pub mod typenum_tests {
// Since all of this is type-level code,
// these tests run at compile-time :-).
use super::*;
use static_assertions::assert_type_eq_all as assert_type_eq;
use typenum::consts::*;
#[test]
fn typenum_len() {
assert_type_eq!(U0, Len<TList![]>);
assert_type_eq!(U1, Len<TList![usize]>);
assert_type_eq!(U2, Len<TList![i32, usize]>);
assert_type_eq!(
U10,
Len<TList![char, char, char, char, char, char, char, char, char, char]>
);
}
#[test]
fn typenum_is_empty() {
assert_type_eq!(B1, IsEmpty<TList![]>);
assert_type_eq!(B0, IsEmpty<TList![i32]>);
}
}