curry

src/SUMMARY.md

@@ -21,5 +21,6 @@
   - [Covariance]()
   - [Option, Vec and BoxFuture<'a>]()
   - [Err Err](./exercises/err_err.md)
+  - [Curry](./exercises/curry.md)
 
 [Topics (Spoilers)](./topics.md)

src/exercises/curry.md

@@ -0,0 +1,30 @@
+# Currying
+
+Implement `curry` and make it pass the tests.
+
+```rust
+# trait Curried<A, B>: FnOnce(A) -> Self::Inner {
+# type C;
+# type Inner: FnOnce(B) -> Self::C;
+# }
+# impl<A, B, C, Inner: FnOnce(B) -> C, F: FnOnce(A) -> Inner> Curried<A, B> for F {
+# type C = C;
+# type Inner = Inner;
+# }
+# fn curry<A, B, C>(f: impl FnOnce(A, B) -> C) -> impl Curried<A, B, C = C> { |a| |b| f(a, b) }
+assert_eq!(curry(|a, b| a * b)(3)(5), 15);
+let mut x = 0;
+curry(|x: &mut i32, y| *x = y)(&mut x)(5);
+assert_eq!(x, 5);
+```
+
+Try solving it in the playground:
+
+```rust,editable,compile_fail
+fn main() {
+    assert_eq!(curry(|a, b| a * b)(3)(5), 15);
+    let mut x = 0;
+    curry(|x: &mut i32, y| *x = y)(&mut x)(5);
+    assert_eq!(x, 5);
+}
+```

src/topics.md

@@ -5,10 +5,10 @@ Rows are ordered based on estimated difficulty.
 | lifetimes\[-adjacent\] | `trait`s           | `struct`s           |
 |------------------------|--------------------|---------------------|
 | [explicit lifetimes]   | [`Fn`?]            | [`Duration`]        |
-| [from reference]       | [`async` `Fn`]     | [All Errors?]       |
-| [extracting lifetimes] | [composition]      | [`RcChars`]         |
-| [`'static` return]     | [exclusive traits] | [`AnyStr`]          |
-|                        | [merging traits]   | [`Result` ordering] |
+| [from reference]       | [`curry`]          | [All Errors?]       |
+| [extracting lifetimes] | [`async` `Fn`]     | [`RcChars`]         |
+| [`'static` return]     | [exclusive traits] | [`Result` ordering] |
+| [composition]          | [merging traits]   | [`AnyStr`]          |
 
 p.s. most of the exercises are actually about `trait`s, this categorisation isn't strict.
 
@@ -26,3 +26,4 @@ p.s. most of the exercises are actually about `trait`s, this categorisation isn'
 [`async` `Fn`]: ./exercises/async_fn.md
 [`'static` return]: ./exercises/get_functions.md
 [`Result` ordering]: ./exercises/err_err.md
+[`curry`]: ./exercises/curry.md