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//! # The `type_operators` macro - a DSL for declaring type operators and type-level logic in Rust. //! //! This crate contains a macro for declaring type operators in Rust. Type operators are like functions //! which act at the type level. The `type_operators` macro works by translating a LISP-y DSL into a big mess of //! traits and impls with associated types. //! //! # The DSL //! //! Let's take a look at this fairly small example: //! //! ```rust //! # #[macro_use] extern crate type_operators; //! type_operators! { //! [A, B, C, D, E] //! //! data Nat { //! P, //! I(Nat = P), //! O(Nat = P), //! } //! } //! # fn main() {} //! ``` //! //! There are two essential things to note in this example. The first is the "gensym list" - Rust does //! not currently have a way to generate unique identifiers, so we have to supply our own. It is on *you* //! to avoid clashes between these pseudo-gensyms and the names of the structs involved! If we put `P`, `I`, or `O` //! into the gensym list, things could get really bad! We'd get type errors at compile-time stemming from trait //! bounds, coming from the definitions of type operators later. Thankfully, the gensym list can be fairly small //! and usually never uses more than two or three symbols. //! //! The second thing is the `data` declaration. This declares a group of structs which fall under a marker trait. //! In our case, `Nat` is the marker trait generated and `P`, `I`, and `O` are the structs generated. This example //! shows an implementation of natural numbers (positive integers, including zero) which are represented as types. //! So, `P` indicates the end of a natural number - think of it as a sort of nil; we're working with a linked list //! here, at the type level. So, `I<P>` would represent "one times twice `P`", which of course comes out to `1`; //! `O<P>` would represent "twice `P`", which of course comes out to zero. If we look at `I` and `O` as bits of a //! binary number, we come out with a sort of reversed binary representation where the "bit" furthest to the left //! is the least significant bit. As such, `O<O<I>>` represents `4`, `I<O<O<I>>>` represents `9`, and so on. //! //! When we write `I(Nat = P)`, the `= P` denotes a default. This lets us write `I`, and have it be inferred to be //! `I<P>`, which is probably what you mean if you just write `I` alone. `Nat` gives a trait bound. To better demonstrate, //! here is (roughly) what the above invocation of `type_operators` expands to: //! //! ```rust //! # use std::marker::PhantomData; //! //! pub trait Nat {} //! //! pub struct P; //! impl Nat for P {} //! //! pub struct I<A: Nat = P>(PhantomData<(A)>); //! impl<A: Nat> Nat for I<A> {} //! //! pub struct O<A: Nat = P>(PhantomData<(A)>); //! impl<A: Nat> Nat for O<A> {} //! # fn main() {} //! ``` //! //! The `Undefined` value looks a little silly, but it allows for the definition of division in a way which uses //! type-level comparison and branching. More on that later. //! //! The above definition has a problem. We cannot *fold* our type-level representation down into a numerical representation. //! That makes our type-level natural numbers useless! That's why `type_operators` provides another way of defining //! type-level representations, the `concrete` declaration: //! //! ```rust //! # #[macro_use] //! # extern crate type_operators; //! //! type_operators! { //! [A, B, C, D, E] //! //! concrete Nat => usize { //! P => 0, //! I(N: Nat = P) => 1 + 2 * N, //! O(N: Nat = P) => 2 * N, //! Undefined => panic!("Undefined type-level arithmetic result!"), //! } //! } //! # fn main() {} //! ``` //! //! This adds an associated function to the `Nat` trait called `reify`, which allows you to turn your type-level //! representations into concrete values of type `usize` (in this case.) If you've ever seen primitive-recursive //! functions, then this should look a bit familiar to you - it's reminiscent of a recursion scheme, which is a //! way of recursing over a value to map it into something else. (See also "catamorphism".) It should be fairly //! obvious how this works, but if not, here's a breakdown: //! //! - `P` always represents zero, so we say that `P => 0`. Simple. //! - `I` represents double its argument plus one. If we annotate our macro's definition with a variable `N`, //! then `type_operators` will automatically call `N::reify()` and substitute that value for your `N` in the //! expression you give it. So, in this way, we define the reification of `I` to be one plus two times the //! value that `N` reifies to. //! - `O` represents double its argument, so this one's straightforward - it's like `I`, but without the `1 +`. //! //! Okay. So now that we've got that under our belts, let's dive into something a bit more complex: let's define //! a type operator for addition. //! //! `type_operators` allows you to define recursive functions. Speaking generally, that's what you'll really need //! to pull this off whatever you do. (And speaking precisely, this whole approach was inspired by primitive-recursion.) //! So let's think about how we can add two binary numbers, starting at the least-significant bit: //! - Obviously, `P + P` should be `P`, since zero plus zero is zero. //! - What about `P + O<N>`, for any natural number `N`? Well, that should be `O<N>`. Same with `I<N>`. As a matter of //! fact, now it looks pretty obvious that whenever we have `P` on one side, we should just say that whatever's on the //! other side is the result. //! So our little table of operations now looks like: //! ```text //! [P, P] => P //! [P, (O N)] => (O N) //! [P, (I N)] => (I N) //! [(O N), P] => (O N) //! [(I N), P] => (I N) //! ``` //! Now you're probably saying, "whoa! That doesn't look like Rust at all! Back up!" And that's because it *isn't.* I made //! a little LISP-like dialect to describe Rust types for this project because it makes things a lot easier to parse in //! macros; specifically, each little atomic type can be wrapped up in a pair of parentheses, while with angle brackets, //! Rust has to parse them as separate tokens. In this setup, `(O N)` means `O<N>`, //! just `P` alone means `P`, etc. etc. The notation `[X, Y] => Z` means "given inputs `X` and `Y`, produce output `Z`." So //! it's a sort of pattern-matching. //! //! Now let's look at the more complex cases. We need to cover all the parts where combinations of `O<N>` and `I<N>` are //! added together. //! - `O<M> + O<N>` should come out to `O<M + N>`. This is a fairly intuitive result, but we can describe it mathematically //! as `2 * m + 2 * n == 2 * (m + n)`. So, it's the distributive law, and most importantly, it cuts down on the *structure* //! of the arguments - we go from adding `O<M>` and `O<N>` to `M` and `N`, whatever they are, and `M` and `N` are clearly //! less complex than `O<M>` and `O<N>`. If we always see that our outputs have less complexity than the inputs, then we're //! that much closer to a proof that our little type operator always terminates with a result! //! - `I<M> + O<N>` and `O<M> + I<N>` should come out to `I<M + N>`. Again, fairly intuitive. We have `1 + 2 * m + 2 * n`, //! which we can package up into `1 + 2 * (m + n)`. //! - `I<M> + I<N>` is the trickiest part here. We have `1 + 2 * m + 1 + 2 * m == 2 + 2 * m + 2 * n == 2 * (1 + m + n)`. We //! can implement this as `I<I + M + N>`, but we can do a little bit better. More on that later, we'll head with the simpler //! implementation for now. //! //! Let's add these to the table: //! ```text //! [P, P] => P //! [P, (O N)] => (O N) //! [P, (I N)] => (I N) //! [(O N), P] => (O N) //! [(I N), P] => (I N) //! // New: //! [(O M), (O N)] => (O (# M N)) //! [(I M), (O N)] => (I (# M N)) //! [(O M), (I N)] => (I (# M N)) //! [(I M), (I N)] => (O (# (# I M) N)) //! ``` //! Here's something new: the `(# ...)` notation. This tells the macro, "hey, we wanna recurse." It's really shorthand //! for a slightly more complex piece of notation, but they both have one thing in common - *when type_operators processes //! the `(# ...)` notation, it uses it to calculate trait bounds.* This is because your type operator won't compile unless //! it's absolutely certain that `(# M N)` will actually have a defined result. At an even higher level, this is the reason //! I wish Rust had "closed type families" - if `P`, `I`, and `O` were in a closed type family `Nat`, Rust could check at compile-time //! and be absolutely sure that `(# M N)` existed for all `M` and `N` that are in the `Nat` family. //! //! So then. Let's load this into an invocation of `type_operators` to see how it looks like. It's pretty close to the table, //! but with a couple additions (I'm leaving out `Undefined` for now because it's not yet relevant): //! //! ```rust //! # #[macro_use] extern crate type_operators; //! //! type_operators! { //! [A, B, C, D, E] //! //! concrete Nat => usize { //! P => 0, //! I(N: Nat = P) => 1 + 2 * N, //! O(N: Nat = P) => 2 * N, //! } //! //! (Sum) Adding(Nat, Nat): Nat { //! [P, P] => P //! forall (N: Nat) { //! [(O N), P] => (O N) //! [(I N), P] => (I N) //! [P, (O N)] => (O N) //! [P, (I N)] => (I N) //! } //! forall (N: Nat, M: Nat) { //! [(O M), (O N)] => (O (# M N)) //! [(I M), (O N)] => (I (# M N)) //! [(O M), (I N)] => (I (# M N)) //! [(I M), (I N)] => (O (# (# M N) I)) //! } //! } //! } //! # fn main() {} //! ``` //! //! There are several things to note. First, the definition `(Sum) Adding(Nat, Nat): Nat`. This says, //! "this type operator takes two `Nat`s as input and outputs a `Nat`." Since addition is implemented //! as a recursive trait under the hood, this means we get a trait definition of the form: //! //! ```rust //! # pub trait Nat {} //! pub trait Adding<A: Nat>: Nat { //! type Output: Nat; //! } //! ``` //! //! The `(Sum)` bit declares a nice, convenient alias for us, so that instead of typing `<X as Adding<Y>>::Output` //! to get the sum of two numbers, we can instead type `Sum<X, Y>`. Much neater. //! //! Second, the "quantifier" sections (the parts with `forall`) avoid Rust complaining about "undeclared type variables." In any given //! generic `impl`, we have to worry about declaring what type variables/generic type parameters we can use in //! that `impl`. The `forall` bit modifies the prelude of the `impl`. For example, `forall (N: Nat)` causes all the //! `impl`s inside its little block to be declared as `impl<N: Nat> ...` instead of `impl ...`, so that we can use //! `N` as a variable inside those expressions. //! //! That just about wraps up our short introduction. To finish, here are the rest of the notations specific to our //! little LISP-y dialect, all of which can only be used on the right-hand side of a rule in the DSL: //! //! - `(@TypeOperator ...)` invokes another type operator (can be the original caller!) and generates the proper trait bounds. //! - `(% ...)` is like `(# ...)`, but does not generate any trait bounds. //! - `(& <type> where (<where_clause>) (<where_clause>) ...)` allows for the definition of custom `where` clauses for a given //! `impl`. It can appear anywhere in the right-hand side of a rule in the DSL, but in general should probably always be //! written at the top-level for consistency. //! //! If questions are had, I may be found either at my email (which is listed on GitHub) or on the `#rust` IRC, where I go by //! the nick `sleffy`. //! /// The `type_operators` macro does a lot of different things. Specifically, there are two things /// it's meant to do: /// 1. Make declaring closed type families easier. (Although they never *really* end up closed... Good enough.) /// 2. Make declaring type operators easier. (Although there are still a lotta problems with this.) /// /// By "closed type family" here, I mean a family of structs which have a marker trait indicating that they /// "belong" to the family. A sort of type-level enum, if you will (if only something like that could truly /// exist in Rust some day!) And by "type operator", I mean a sort of function which acts on types and returns /// a type. In the following example, the natural numbers (encoded in binary here) are our "closed type family", /// and addition, subtraction, multiplication, division, etc. etc. are all our type operators. /// /// You should probably read the top-level documentation before you look at this more complex example. /// /// ``` /// # #[macro_use] /// # extern crate type_operators; /// /// type_operators! { /// [A, B, C, D, E] // The gensym list. Be careful not to have these collide with your struct names! /// /// // If I used `data` instead of concrete, no automatic `reify` function would be provided. /// // But since I did, we have a sort of inductive thing going on here, by which we can transform /// // any instance of this type into the reified version. /// /// // data Nat { /// // P, /// // I(Nat = P), /// // O(Nat = P), /// // } /// /// concrete Nat => usize { /// P => 0, /// I(N: Nat = P) => 1 + 2 * N, /// O(N: Nat = P) => 2 * N, /// Undefined => panic!("Undefined type-level arithmetic result!"), /// } /// /// // It's not just for natural numbers! Yes, we can do all sorts of logic here. However, in /// // this example, `Bool` is used later on in implementations that are hidden from you due /// // to their complexity. /// concrete Bool => bool { /// False => false, /// True => true, /// } /// /// (Pred) Predecessor(Nat): Nat { /// [Undefined] => Undefined /// [P] => Undefined /// forall (N: Nat) { /// [(O N)] => (I (# N)) /// [(I N)] => (O N) /// } /// } /// /// (Succ) Successor(Nat): Nat { /// [Undefined] => Undefined /// [P] => I /// forall (N: Nat) { /// [(O N)] => (I N) /// [(I N)] => (O (# N)) /// } /// } /// /// (Sum) Adding(Nat, Nat): Nat { /// [P, P] => P /// forall (N: Nat) { /// [(O N), P] => (O N) /// [(I N), P] => (I N) /// [P, (O N)] => (O N) /// [P, (I N)] => (I N) /// } /// forall (N: Nat, M: Nat) { /// [(O M), (O N)] => (O (# M N)) /// [(I M), (O N)] => (I (# M N)) /// [(O M), (I N)] => (I (# M N)) /// [(I M), (I N)] => (O (# (# M N) I)) /// } /// } /// /// (Difference) Subtracting(Nat, Nat): Nat { /// forall (N: Nat) { /// [N, P] => N /// } /// forall (N: Nat, M: Nat) { /// [(O M), (O N)] => (O (# M N)) /// [(I M), (O N)] => (I (# M N)) /// [(O M), (I N)] => (I (# (# M N) I)) /// [(I M), (I N)] => (O (# M N)) /// } /// } /// /// (Product) Multiplying(Nat, Nat): Nat { /// forall (N: Nat) { /// [P, N] => P /// } /// forall (N: Nat, M: Nat) { /// [(O M), N] => (# M (O N)) /// [(I M), N] => (@Adding N (# M (O N))) /// } /// } /// /// (If) NatIf(Bool, Nat, Nat): Nat { /// forall (T: Nat, U: Nat) { /// [True, T, U] => T /// [False, T, U] => U /// } /// } /// /// (NatIsUndef) NatIsUndefined(Nat): Bool { /// [Undefined] => True /// [P] => False /// forall (M: Nat) { /// [(O M)] => False /// [(I M)] => False /// } /// } /// /// (NatUndef) NatUndefined(Nat, Nat): Nat { /// forall (M: Nat) { /// [Undefined, M] => Undefined /// [P, M] => M /// } /// forall (M: Nat, N: Nat) { /// [(O N), M] => M /// [(I N), M] => M /// } /// } /// /// (TotalDifference) TotalSubtracting(Nat, Nat): Nat { /// [P, P] => P /// [Undefined, P] => Undefined /// forall (N: Nat) { /// [N, Undefined] => Undefined /// [P, (O N)] => (# P N) /// [P, (I N)] => Undefined /// [(O N), P] => (O N) /// [(I N), P] => (I N) /// [Undefined, (O N)] => Undefined /// [Undefined, (I N)] => Undefined /// } /// forall (N: Nat, M: Nat) { /// [(O M), (O N)] => (@NatUndefined (# M N) (O (# M N))) /// [(I M), (O N)] => (@NatUndefined (# M N) (I (# M N))) /// [(O M), (I N)] => (@NatUndefined (# (# M N) I) (I (# (# M N) I))) /// [(I M), (I N)] => (@NatUndefined (# M N) (O (# M N))) /// } /// } /// /// (Quotient) Quotienting(Nat, Nat): Nat { /// forall (D: Nat) { /// [Undefined, D] => Undefined /// [P, D] => (@NatIf (@NatIsUndefined (@TotalSubtracting P D)) O (@Successor (# (@TotalSubtracting P D) D))) /// } /// forall (N: Nat, D: Nat) { /// [(O N), D] => (@NatIf (@NatIsUndefined (@TotalSubtracting (O N) D)) O (@Successor (# (@TotalSubtracting (O N) D) D))) /// [(I N), D] => (@NatIf (@NatIsUndefined (@TotalSubtracting (I N) D)) O (@Successor (# (@TotalSubtracting (I N) D) D))) /// } /// } /// /// (Remainder) Remaindering(Nat, Nat): Nat { /// forall (D: Nat) { /// [Undefined, D] => Undefined /// [P, D] => (@NatIf (@NatIsUndefined (@TotalSubtracting P D)) P (# (@TotalSubtracting P D) D)) /// } /// forall (N: Nat, D: Nat) { /// [(O N), D] => (@NatIf (@NatIsUndefined (@TotalSubtracting (O N) D)) (O N) (# (@TotalSubtracting (O N) D) D)) /// [(I N), D] => (@NatIf (@NatIsUndefined (@TotalSubtracting (I N) D)) (I O) (# (@TotalSubtracting (I N) D) D)) /// } /// } /// } /// /// # fn main() { /// assert_eq!(<I<I> as Nat>::reify(), 3); /// assert_eq!(<I<O<I>> as Nat>::reify(), 5); /// assert_eq!(<Sum<I<O<I>>, I<I>> as Nat>::reify(), 8); /// assert_eq!(<Difference<I<I>, O<I>> as Nat>::reify(), 1); /// assert_eq!(<Difference<O<O<O<I>>>, I<I>> as Nat>::reify(), 5); /// assert_eq!(<Product<I<I>, I<O<I>>> as Nat>::reify(), 15); /// assert_eq!(<Quotient<I<I>, O<I>> as Nat>::reify(), 1); /// assert_eq!(<Remainder<I<O<O<I>>>, O<O<I>>> as Nat>::reify(), 1); /// # } /// ``` #[macro_export] macro_rules! type_operators { ($gensym:tt data $name:ident { $($stuff:tt)* } $($rest:tt)*) => { pub trait $name {} _tlsm_data!($name $gensym $($stuff)*); type_operators!($gensym $($rest)*); }; ($gensym:tt concrete $name:ident => $output:ty { $($stuff:tt)* } $($rest:tt)*) => { pub trait $name { fn reify() -> $output; } _tlsm_concrete!($name $output; $gensym $($stuff)*); type_operators!($gensym $($rest)*); }; ($gensym:tt ($alias:ident) $machine:ident ($($kind:tt),*): $out:tt { $($states:tt)* } $($rest:tt)*) => { _tlsm_machine!($alias $machine $gensym [$($kind),*] [] $out); _tlsm_states!($machine $($states)*); type_operators!($gensym $($rest)*); }; ($gensym:tt) => {}; } #[macro_export] macro_rules! _tlsm_parse_type { (($parameterized:ident $($arg:tt)*)) => { $parameterized<$(_tlsm_parse_type!($arg)),*> }; ($constant:ident) => { $constant }; } #[macro_export] macro_rules! _tlsm_states { (@bounds $machine:ident $implinfo:tt [$($bounds:tt)*] [$($queue:tt)*] (& $arg:tt where $($extra:tt)*)) => { _tlsm_states!(@bounds $machine $implinfo [$($bounds)* $($extra)*] [$($queue)*] $arg); }; (@bounds $machine:ident $implinfo:tt $bounds:tt [$($queue:tt)*] (% $arg:tt $($more:tt)*)) => { _tlsm_states!(@bounds $machine $implinfo $bounds [$($more)* $($queue)*] $arg); }; (@bounds $machine:ident $implinfo:tt [$($bounds:tt)*] [$($queue:tt)*] (# $arg:tt $($more:tt)+)) => { _tlsm_states!(@bounds $machine $implinfo [$($bounds)* (_tlsm_states!(@output $machine $arg): $machine< $(_tlsm_states!(@output $machine $more)),+ >)] [$($more)* $($queue)*] $arg); }; (@bounds $machine:ident $implinfo:tt [$($bounds:tt)*] [$($queue:tt)*] (@ $external:ident $arg:tt $($more:tt)+)) => { _tlsm_states!(@bounds $machine $implinfo [$($bounds)* (_tlsm_states!(@output $machine $arg): $external< $(_tlsm_states!(@output $machine $more)),+ >)] [$($more)* $($queue)*] $arg); }; (@bounds $machine:ident $implinfo:tt [$($bounds:tt)*] [$($queue:tt)*] (# $arg:tt)) => { _tlsm_states!(@bounds $machine $implinfo [$($bounds)* (_tlsm_states!(@output $machine $arg): $machine)] [$($queue)*] $arg); }; (@bounds $machine:ident $implinfo:tt [$($bounds:tt)*] [$($queue:tt)*] (@ $external:ident $arg:tt)) => { _tlsm_states!(@bounds $machine $implinfo [$($bounds)* (_tlsm_states!(@output $machine $arg): $external)] [$($queue)*] $arg); }; (@bounds $machine:ident $implinfo:tt $bounds:tt [$($queue:tt)*] ($parameterized:ident $arg:tt $($args:tt)*)) => { _tlsm_states!(@bounds $machine $implinfo $bounds [$($args)* $($queue)*] $arg); }; (@bounds $machine:ident $implinfo:tt $bounds:tt [$next:tt $($queue:tt)*] $constant:ident) => { _tlsm_states!(@bounds $machine $implinfo $bounds [$($queue)*] $next); }; (@bounds $machine:ident { $($implinfo:tt)* } $bounds:tt [] $constant:ident) => { _tlsm_states!(@implement $machine $bounds $($implinfo)*); }; (@dispatch $machine:ident forall $quantified:tt { $($input:tt => $output:tt)* }) => { $(_tlsm_states!(@bounds $machine { $quantified $input => $output } [] [] $output);)* }; (@dispatch $machine:ident $input:tt => $output:tt) => { _tlsm_states!(@bounds $machine { () $input => $output } [] [] $output); }; (@implement $machine:ident [$(($($constraint:tt)*))+] ($($bounds:tt)+) [$head:tt $(, $input:tt)+] => $output:tt) => { impl<$($bounds)+> $machine< $(_tlsm_parse_type!($input)),+ > for _tlsm_parse_type!($head) where $($($constraint)*),+ { type Output = _tlsm_states!(@output $machine $output); } }; (@implement $machine:ident [$(($($constraint:tt)*))+] ($($bounds:tt)+) [$head:tt] => $output:tt) => { impl<$($bounds)+> $machine for _tlsm_parse_type!($head) where $($($constraint)*),+ { type Output = _tlsm_states!(@output $machine $output); } }; (@implement $machine:ident [$(($($constraint:tt)*))+] () [$head:tt $(, $input:tt)+] => $output:tt) => { impl $machine< $(_tlsm_parse_type!($input)),+ > for _tlsm_parse_type!($head) where $($($constraint)*),+ { type Output = _tlsm_states!(@output $machine $output); } }; (@implement $machine:ident [$(($($constraint:tt)*))+] () [$head:tt] => $output:tt) => { impl $machine for _tlsm_parse_type!($head) where $($($constraint)*),+ { type Output = _tlsm_states!(@output $machine $output); } }; (@implement $machine:ident [] ($($bounds:tt)+) [$head:tt $(, $input:tt)+] => $output:tt) => { impl<$($bounds)+> $machine< $(_tlsm_parse_type!($input)),+ > for _tlsm_parse_type!($head) { type Output = _tlsm_states!(@output $machine $output); } }; (@implement $machine:ident [] ($($bounds:tt)+) [$head:tt] => $output:tt) => { impl<$($bounds)+> $machine for _tlsm_parse_type!($head) { type Output = _tlsm_states!(@output $machine $output); } }; (@implement $machine:ident [] () [$head:tt $(, $input:tt)+] => $output:tt) => { impl $machine< $(_tlsm_parse_type!($input)),+ > for _tlsm_parse_type!($head) { type Output = _tlsm_states!(@output $machine $output); } }; (@implement $machine:ident [] () [$head:tt] => $output:tt) => { impl $machine for _tlsm_parse_type!($head) { type Output = _tlsm_states!(@output $machine $output); } }; (@output $machine:ident (& $arg:tt $($extra:tt)*)) => { _tlsm_states!(@output $machine $arg) }; (@output $machine:ident (# $arg:tt $($more:tt)+)) => { <_tlsm_states!(@output $machine $arg) as $machine< $(_tlsm_states!(@output $machine $more)),+ >>::Output }; (@output $machine:ident (# $arg:tt)) => { <_tlsm_states!(@output $machine $arg) as $machine>::Output }; (@output $machine:ident (% $arg:tt $($more:tt)+)) => { <_tlsm_states!(@output $machine $arg) as $machine< $(_tlsm_states!(@output $machine $more)),+ >>::Output }; (@output $machine:ident (% $arg:tt)) => { <_tlsm_states!(@output $machine $arg) as $machine>::Output }; (@output $machine:ident (@ $external:ident $arg:tt $($more:tt)+)) => { <_tlsm_states!(@output $machine $arg) as $external< $(_tlsm_states!(@output $machine $more)),+ >>::Output }; (@output $machine:ident (@ $external:ident $arg:tt)) => { <_tlsm_states!(@output $machine $arg) as $external>::Output }; (@output $machine:ident ($parameterized:ident $($arg:tt)+)) => { $parameterized<$(_tlsm_states!(@output $machine $arg)),+> }; (@output $machine:ident $constant:ident) => { $constant }; ($machine:ident $($head:tt $body:tt $tail:tt)*) => { $(_tlsm_states!(@dispatch $machine $head $body $tail);)* }; } #[macro_export] macro_rules! _tlsm_machine { ($alias:ident $machine:ident [$gensym:ident $(, $gensyms:ident)*] [_ $(, $kinds:tt)*] [$($accum:tt)*] $out:tt) => { _tlsm_machine!($alias $machine [$($gensyms),*] [$($kinds),*] [$($accum)* ($gensym)] $out); }; ($alias:ident $machine:ident [$gensym:ident $(, $gensyms:ident)*] [$kind:tt $(, $kinds:tt)*] [$($accum:tt)*] $out:tt) => { _tlsm_machine!($alias $machine [$($gensyms),*] [$($kinds),*] [$($accum)* ($gensym: $kind)] $out); }; ($alias:ident $machine:ident $gensym:tt [] [($fsym:ident $($fbound:tt)*) $(($sym:ident $($bound:tt)*))+] _) => { pub trait $machine < $($sym $($bound)*),+ > $($fbound)* { type Output; } pub type $alias < $fsym $($fbound)* $(, $sym $($bound)*)+ > = <$fsym as $machine< $($sym),+ >>::Output; }; ($alias:ident $machine:ident $gensym:tt [] [($fsym:ident $($fbound:tt)*)] _) => { pub trait $machine $($fbound)* { type Output; } pub type $alias < $fsym $($fbound)* > = <$fsym as $machine>::Output; }; ($alias:ident $machine:ident $gensym:tt [] [($fsym:ident $($fbound:tt)*) $(($sym:ident $($bound:tt)*))+] $out:ident) => { pub trait $machine < $($sym $($bound)*),+ > $($fbound)* { type Output: $out; } pub type $alias < $fsym $($fbound)* $(, $sym $($bound)*)+ > = <$fsym as $machine< $($sym),+ >>::Output; }; ($alias:ident $machine:ident $gensym:tt [] [($fsym:ident $($fbound:tt)*)] $out:ident) => { pub trait $machine $($fbound)* { type Output: $out; } pub type $alias < $fsym $($fbound)* > = <$fsym as $machine>::Output; }; } #[macro_export] macro_rules! _tlsm_data { ($group:ident @parameterized $name:ident [$gensym:ident $(, $next:ident)*] [$($args:tt)*] [$($bounds:tt)*] [$($phantom:tt)*] $kind:ident = $default:ty $(, $($rest:tt)*)*) => { _tlsm_data!($group @parameterized $name [$($next),*] [$($args)* ($gensym: $kind = $default)] [$($bounds)* ($gensym: $kind)] [$($phantom)* ($gensym)] $($($rest)*),*); }; ($group:ident @parameterized $name:ident [$gensym:ident $(, $next:ident)*] [$($args:tt)*] [$($bounds:tt)*] [$($phantom:tt)*] $kind:ident $($rest:tt)*) => { _tlsm_data!($group @parameterized $name [$($next),*] [$($args)* ($gensym: $kind)] [$($bounds)* ($gensym: $kind)] [$($phantom)* ($gensym)] $($rest)*); }; ($group:ident @parameterized $name:ident $gensyms:tt [$(($($args:tt)*))*] [$(($($bounds:tt)*))*] [$(($($phantom:tt)*))*]) => { pub struct $name < $($($args)*),* >(::std::marker::PhantomData<($($($phantom)*),*)>); impl< $($($bounds)*),* > $group for $name<$($($phantom)*),*> {} }; ($group:ident $gensym:tt $name:ident, $($rest:tt)*) => { pub struct $name; impl $group for $name {} _tlsm_data!($group $gensym $($rest)*); }; ($group:ident $gensym:tt $name:ident($($args:tt)*), $($rest:tt)*) => { _tlsm_data!($group @parameterized $name $gensym [] [] [] $($args)*); _tlsm_data!($group $gensym $($rest)*); }; ($group:ident $gensym:tt) => {}; } #[macro_export] macro_rules! _tlsm_concrete { ($group:ident $output:ty; @parameterized $name:ident => $value:expr; $gensym:tt [$($args:tt)*] [$($bounds:tt)*] [$($syms:ident)*] $sym:ident: $kind:ident = $default:ty $(, $($rest:tt)*)*) => { _tlsm_concrete!($group $output; @parameterized $name => $value; $gensym [$($args)* ($sym: $kind = $default)] [$($bounds)* ($sym: $kind)] [$($syms)* $sym] $($($rest)*),*); }; ($group:ident $output:ty; @parameterized $name:ident => $value:expr; $gensym:tt [$($args:tt)*] [$($bounds:tt)*] [$($syms:ident)*] $sym:ident: $kind:ident $(, $($rest:tt)*)*) => { _tlsm_concrete!($group $output; @parameterized $name => $value; $gensym [$($args)* ($sym: $kind)] [$($bounds)* ($sym: $kind)] [$($syms)* $sym] $($($rest)*),*); }; ($group:ident $output:ty; @parameterized $name:ident => $value:expr; [$gensym:ident $(, $next:ident)*] [$($args:tt)*] [$($bounds:tt)*] $syms:tt $kind:ident = $default:ty $(, $($rest:tt)*)*) => { _tlsm_concrete!($group $output; @parameterized $name => $value; [$($next),*] [$($args)* ($gensym: $kind = $default)] [$($bounds)* ($gensym: $kind)] $syms $($($rest)*),*); }; ($group:ident $output:ty; @parameterized $name:ident => $value:expr; [$gensym:ident $(, $next:ident)*] [$($args:tt)*] [$($bounds:tt)*] $syms:tt $kind:ident $(, $($rest:tt)*)*) => { _tlsm_concrete!($group $output; @parameterized $name => $value; [$($next),*] [$($args)* ($gensym: $kind)] [$($bounds)* ($gensym: $kind)] $syms $($($rest)*),*); }; ($group:ident $output:ty; @parameterized $name:ident => $value:expr; $gensyms:tt [$(($tysym:ident: $($args:tt)*))*] [$(($bsym:ident: $bound:ident))*] [$($sym:ident)*]) => { pub struct $name < $($tysym: $($args)*),* >(::std::marker::PhantomData<($($tysym),*)>); impl< $($bsym: $bound),* > $group for $name<$($bsym),*> { #[allow(non_snake_case)] fn reify() -> $output { $(let $sym = <$sym>::reify();)* $value } } }; ($group:ident $output:ty; $gensym:tt $name:ident => $value:expr, $($rest:tt)*) => { pub struct $name; impl $group for $name { fn reify() -> $output { $value } } _tlsm_concrete!($group $output; $gensym $($rest)*); }; ($group:ident $output:ty; $gensym:tt $name:ident($($args:tt)*) => $value:expr, $($rest:tt)*) => { _tlsm_concrete!($group $output; @parameterized $name => $value; $gensym [] [] [] $($args)*); _tlsm_concrete!($group $output; $gensym $($rest)*); }; ($group:ident $output:ty; $gensym:tt) => {}; }