derive(CovariantFunctor)

radn-derive/src/lib.rs

@@ -5,7 +5,7 @@ use syn::{parse_macro_input, parse_quote, DeriveInput, GenericParam, Generics};
 pub fn derive_shared_functor(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
     let input = parse_macro_input!(input as DeriveInput);
     let name = input.ident;
-    let generics = add_trait_bounds(input.generics);
+    let generics = add_clone_bounds(input.generics);
     let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
     let expanded = quote! {
         impl #impl_generics SharedFunctor for #name #ty_generics #where_clause {
@@ -31,7 +31,7 @@ pub fn derive_shared_functor(input: proc_macro::TokenStream) -> proc_macro::Toke
     proc_macro::TokenStream::from(expanded)
 }
 
-fn add_trait_bounds(mut generics: Generics) -> Generics {
+fn add_clone_bounds(mut generics: Generics) -> Generics {
     for param in &mut generics.params {
         if let GenericParam::Type(ref mut type_param) = *param {
             type_param.bounds.push(parse_quote!(Clone));
@@ -39,3 +39,22 @@ fn add_trait_bounds(mut generics: Generics) -> Generics {
     }
     generics
 }
+
+#[proc_macro_derive(CovariantFunctor)]
+pub fn derive_covariant_functor(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    let input = parse_macro_input!(input as DeriveInput);
+    let name = input.ident;
+    let generics = input.generics;
+    let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
+    let expanded = quote! {
+        impl #impl_generics CovariantFunctor for #name #ty_generics #where_clause {
+            fn variate<'a: 'b, 'b, A: 'a>(fa: Self::F<'a, A>) -> Self::F<'b, A>
+            where
+                Self: 'a,
+            {
+                fa
+            }
+        }
+    };
+    proc_macro::TokenStream::from(expanded)
+}

src/func.rs

@@ -19,7 +19,7 @@ pub mod tests;
 
 pub use self::istate::IState;
 use self::istate::IStateClass;
-pub use radn_derive::SharedFunctor;
+pub use radn_derive::{CovariantFunctor, SharedFunctor};
 
 /// Part of Haskell's `Functor f` responsible to use `f a`.
 ///

src/func/classes/future.rs

@@ -9,6 +9,7 @@ use futures::{future::Shared, join, FutureExt};
 
 use crate::func::*;
 
+#[derive(CovariantFunctor)]
 pub struct FutureClass;
 
 impl WeakFunctor for FutureClass {

src/func/classes/lazy.rs

@@ -11,6 +11,7 @@ use std::{cell::RefCell, rc::Rc};
 
 use crate::func::*;
 
+#[derive(CovariantFunctor)]
 pub struct LazyClass;
 
 impl WeakFunctor for LazyClass {

src/func/classes/option.rs

@@ -9,7 +9,7 @@
 
 use crate::func::*;
 
-#[derive(SharedFunctor)]
+#[derive(SharedFunctor, CovariantFunctor)]
 pub struct OptionClass;
 
 impl WeakFunctor for OptionClass {

src/func/classes/result.rs

@@ -9,7 +9,7 @@
 
 use crate::func::*;
 
-#[derive(SharedFunctor)]
+#[derive(SharedFunctor, CovariantFunctor)]
 pub struct ResultClass<E>(E);
 
 impl<E> WeakFunctor for ResultClass<E> {

src/func/classes/solo.rs

@@ -4,7 +4,7 @@
 
 use crate::func::*;
 
-#[derive(SharedFunctor)]
+#[derive(SharedFunctor, CovariantFunctor)]
 pub struct SoloClass;
 
 impl WeakFunctor for SoloClass {