fp_macros/

lib.rs

//! Procedural macros for the [`fp-library`](https://docs.rs/fp-library/latest/fp_library/) crate.
//!
//! This crate provides macros for generating and working with Higher-Kinded Type (HKT) traits.
//! It includes:
//! - `Kind!`: Generates the name of a `Kind` trait based on its signature.
//! - `def_kind!`: Defines a new `Kind` trait.
//! - `impl_kind!`: Implements a `Kind` trait for a brand.
//! - `Apply!`: Applies a brand to type arguments.

use apply::{ApplyInput, apply_impl};
use def_kind::def_kind_impl;
use generate::generate_name;
use impl_kind::{ImplKindInput, impl_kind_impl};
use parse::KindInput;
use proc_macro::TokenStream;
use quote::quote;
use syn::parse_macro_input;

pub(crate) mod apply;
pub(crate) mod canonicalize;
pub(crate) mod def_kind;
pub(crate) mod generate;
pub(crate) mod impl_kind;
pub(crate) mod parse;

#[cfg(test)]
mod property_tests;

/// Generates the name of a `Kind` trait based on its signature.
///
/// This macro takes a list of associated type definitions, similar to a trait definition.
///
/// # Examples
///
/// ```ignore
/// // Simple signature
/// let name = Kind!(type Of<T>;);
///
/// // Signature with bounds and lifetimes
/// let name = Kind!(type Of<'a, T: Display>: Debug;);
///
/// // Multiple associated types
/// let name = Kind!(
///     type Of<T>;
///     type SendOf<T>: Send;
/// );
/// ```
///
/// # Limitations
///
/// Due to Rust syntax restrictions, this macro cannot be used directly in positions where a
/// concrete path is expected by the parser, such as:
/// * Supertrait bounds: `trait MyTrait: Kind!(...) {}` (Invalid)
/// * Type aliases: `type MyKind = Kind!(...);` (Invalid)
/// * Trait aliases: `trait MyKind = Kind!(...);` (Invalid)
///
/// In these cases, you must use the generated name directly (e.g., `Kind_...`).
#[proc_macro]
#[allow(non_snake_case)]
pub fn Kind(input: TokenStream) -> TokenStream {
	let input = parse_macro_input!(input as KindInput);
	let name = generate_name(&input);
	quote!(#name).into()
}

/// Defines a new `Kind` trait.
///
/// This macro generates a trait definition for a Higher-Kinded Type signature.
/// It takes a list of associated type definitions, similar to a trait definition.
///
/// # Examples
///
/// ```ignore
/// // Simple definition
/// def_kind!(type Of<T>;);
///
/// // Definition with bounds and lifetimes
/// def_kind!(type Of<'a, T: Display>: Debug;);
///
/// // Multiple associated types
/// def_kind!(
///     type Of<T>;
///     type SendOf<T>: Send;
/// );
/// ```
#[proc_macro]
pub fn def_kind(input: TokenStream) -> TokenStream {
	let input = parse_macro_input!(input as KindInput);
	def_kind_impl(input).into()
}

/// Implements a `Kind` trait for a brand.
///
/// This macro simplifies the implementation of a generated `Kind` trait for a specific
/// brand type. It infers the correct `Kind` trait to implement based on the signature
/// of the associated types provided in the block.
///
/// The signature (names, parameters, and bounds) of the associated types must match
/// the definition used in [`def_kind!`] or [`Kind!`] to ensure the correct trait is implemented.
///
/// # Syntax
///
/// ```ignore
/// impl_kind! {
///     // Optional impl generics
///     impl<Generics> for BrandType
///     // Optional where clause
///     where Bounds
///     {
///         type AssocName<Params> = ConcreteType;
///         // ... more associated types
///     }
/// }
/// ```
///
/// # Examples
///
/// ```ignore
/// // Simple implementation
/// impl_kind! {
///     for OptionBrand {
///         type Of<A> = Option<A>;
///     }
/// }
///
/// // Implementation with generics
/// impl_kind! {
///     impl<E> for ResultBrand<E> {
///         type Of<A> = Result<A, E>;
///     }
/// }
///
/// // Implementation with where clause and multiple types
/// impl_kind! {
///     impl<E> for MyBrand<E> where E: Clone {
///         type Of<A> = MyType<A, E>;
///         type SendOf<A> = MySendType<A, E>;
///     }
/// }
///
/// // Implementation matching a `Kind` with bounds
/// // Corresponds to: def_kind!(type Of<T: Display>;);
/// impl_kind! {
///     for DisplayBrand {
///         // Bounds here are used to infer the correct `Kind` trait name
///         type Of<T: Display> = DisplayType<T>;
///     }
/// }
/// ```
#[proc_macro]
pub fn impl_kind(input: TokenStream) -> TokenStream {
	let input = parse_macro_input!(input as ImplKindInput);
	impl_kind_impl(input).into()
}

/// Applies a brand to type arguments.
///
/// This macro projects a brand type to its concrete type using the appropriate
/// `Kind` trait. It uses a syntax that mimics a fully qualified path, where the
/// `Kind` trait is specified by its signature.
///
/// # Syntax
///
/// ```ignore
/// Apply!(<Brand as Kind!( KindSignature )>::AssocType<Args>)
/// ```
///
/// * `Brand`: The brand type (e.g., `OptionBrand`).
/// * `KindSignature`: A list of associated type definitions defining the `Kind` trait schema.
/// * `AssocType`: The associated type to project (e.g., `Of`).
/// * `Args`: The concrete arguments to apply.
///
/// # Examples
///
/// ```ignore
/// // Applies MyBrand to lifetime 'static and type String.
/// type Concrete = Apply!(<MyBrand as Kind!( type Of<'a, T>; )>::Of<'static, String>);
///
/// // Applies MyBrand to a generic type T with bounds.
/// type Concrete = Apply!(<MyBrand as Kind!( type Of<T: Clone>; )>::Of<T>);
///
/// // Complex example with lifetimes, types, and output bounds.
/// type Concrete = Apply!(<MyBrand as Kind!( type Of<'a, T: Clone + Debug>: Display; )>::Of<'a, T>);
///
/// // Use a custom associated type for projection.
/// type Concrete = Apply!(<MyBrand as Kind!( type Of<T>; type SendOf<T>; )>::SendOf<T>);
/// ```
#[proc_macro]
#[allow(non_snake_case)]
pub fn Apply(input: TokenStream) -> TokenStream {
	let input = parse_macro_input!(input as ApplyInput);
	apply_impl(input).into()
}