Releae 0.9.13

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "typle"
-version = "0.9.12"
+version = "0.9.13"
 edition = "2021"
 description = "Generic tuple bounds and transformations"
 license = "MIT"

src/lib.rs

@@ -682,6 +682,11 @@ pub fn typle_any(item: proc_macro::TokenStream) -> proc_macro::TokenStream {
 ///     None::<(i32, &str)>
 /// );
 /// ```
+///
+/// The `typle_fold!` macro can also be used for recursive types. See the
+/// [example in the tests].
+///
+/// [example in the tests]: https://github.com/jongiddy/typle/blob/main/tests/compile/typle_fold.rs
 #[proc_macro]
 pub fn typle_fold(item: proc_macro::TokenStream) -> proc_macro::TokenStream {
     Error::new_spanned(

tests/compile/typle_fold.rs

@@ -0,0 +1,28 @@
+use typle::typle;
+
+pub struct Something {}
+
+pub trait IsUseful<Other> {
+    type State: IsUseful<Something>;
+}
+
+pub trait UsefulTrait {
+    type UsefulType: IsUseful<Something>;
+}
+
+#[typle(Tuple for 1..=3)]
+impl<T: Tuple> UsefulTrait for T
+where
+    T<_>: UsefulTrait,
+    typle_bound!(i in 1..T::LEN => T<{i}>::UsefulType):IsUseful<
+        typle_fold!(
+            T0::UsefulType;
+            j in 1..i => |Inner| <T<{j}>::UsefulType as IsUseful<Inner>>::State
+        ),
+    >,
+{
+    type UsefulType = typle_fold!(
+        T0::UsefulType;
+        j in 1..T::LEN => |Inner| <T<{j}>::UsefulType as IsUseful<Inner>>::State
+    );
+}