polish

src/assignments/assignment08/small_exercises.rs

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+//! Assignment 08: First-class functions.
+
+/// Repeat
+///
+/// Returns an anonymous function that applies the given function `f` for `n` times.
+/// For instance, `repeat(3, f)(x)` roughly translates to `f(f(f(x)))`.
+///
+/// Refer `test_repeat` in `assignment08_grade.rs` for detailed examples.
+pub fn repeat<T, F: FnMut(T) -> T>(n: usize, mut f: F) -> impl FnMut(T) -> T {
+    todo!();
+    f // This line has been added to prevent compile error. You can erase this line.
+}
+
+/// Funny Map
+///
+/// Applies the given function `f` for `i` times for the `i`-th element of the given vector.
+///
+/// For instance, `funny_map(f, [v0, v1, v2, v3])` roughly translates to `[v0, f(v1), f(f(v2)), f(f(f(v3)))]`.
+///
+/// Refer `test_funny_map` in `assignment08_grade.rs` for detailed examples.
+pub fn funny_map<T, F: Fn(T) -> T>(f: F, vs: Vec<T>) -> Vec<T> {
+    todo!()
+}
+
+/// Count Repeat
+///
+/// Returns the number of the elements of the set
+/// {x, f(x), f(f(x)), f(f(f(x))), ...}.
+/// You may assume that the answer is finite and small enough.
+///
+/// Refer `test_count_repeat` in `assignment08_grade.rs` for detailed examples.
+pub fn count_repeat<T, F: Fn(T) -> T>(f: F, x: T) -> usize
+where
+    T: PartialEq + Copy,
+{
+    todo!()
+}
+
+/// Either `T1`, or `T2`.
+///
+/// Fill out `map` method for this type.
+#[derive(Debug, PartialEq, Eq)]
+pub enum Either2<T1, T2> {
+    /// Case 1.
+    Case1 {
+        /// The inner value.
+        inner: T1,
+    },
+    /// Case 2.
+    Case2 {
+        /// The inner value.
+        inner: T2,
+    },
+}
+
+impl<T1, T2> Either2<T1, T2> {
+    /// Maps the inner value.
+    ///
+    /// If the inner value is case 1, apply `f1`, and if it is case 2, apply `f2`.
+    ///
+    /// Refer `test_either2_map` in `assignment08_grade.rs` for detailed examples.
+    pub fn map<U1, U2, F1, F2>(self, f1: F1, f2: F2) -> Either2<U1, U2>
+    where
+        F1: FnOnce(T1) -> U1,
+        F2: FnOnce(T2) -> U2,
+    {
+        todo!()
+    }
+}