more exercises

src/SUMMARY.md

@@ -3,4 +3,7 @@
 [Overview](./overview.md)
 
 - [Chapter 1](./chapter_1.md)
-  - [`A`/`A1`/`A2`](./exercises/multiple_blanket.md)
+  - [test0.rs (bind)](./exercises/bind.md)
+  - [test1.rs (refbind)](./exercises/refbind.md)
+  - [A/A1/A2](./exercises/multiple_blanket.md)
+  - [BoolStream](./exercises/bool_stream.md)

src/exercises/bind.md

@@ -0,0 +1,27 @@
+```rust
+# mod __ {
+fn bind<T, F: FnOnce(T) -> Option<T>>(f: F, fa: Option<T>) -> Option<T> {
+    match fa {
+        Some(a) => f(a),
+        None => None,
+    }
+}
+# }
+# fn bind<T, F: FnOnce(T) -> Option<T>>(f: F, fa: Option<T>) -> Option<T> { fa.and_then(f) }
+
+// don't change anything below
+
+assert_eq!(bind(|x: i32| Some(x + 3), Some(2)), Some(5));
+assert_eq!(bind(|x: i32| Some(x + 3), None), None);
+assert_eq!(bind(|_: i32| None, Some(2)), None);
+assert_eq!(bind(|_: i32| None, None), None);
+
+assert_eq!(bind(|x: &str| Some(x), Some("apple")), Some("apple"));
+assert_eq!(bind(|_: &str| Some("banana"), Some("apple")), Some("banana"));
+
+let banana = "banana".to_string();
+assert_eq!(
+    bind(|_: String| Some(banana), Some("apple".to_string())),
+    Some("banana".to_string()),
+);
+```

src/exercises/bool_stream.md

@@ -0,0 +1,61 @@
+Make `test_covariance` compile by making `BoolStream<'a>` covariant `'a`.
+- Can only change implementation details of `BoolStream` and its methods and add extra items outside of what's given, i.e. no signature/test change.
+- Changed version must behave the same way.
+```rust
+pub struct BoolStream<'a>(
+    // change this
+# /*
+    Box<dyn 'a + FnOnce() -> (bool, BoolStream<'a>)>,
+# */ Box<dyn 'a + Next>
+);
+
+impl<'a> BoolStream<'a> {
+    pub fn new(f: impl 'a + FnOnce() -> (bool, Self)) -> Self {
+        // maybe change this
+# /*
+        Self(Box::new(f))
+# */ Self(Box::new(Wrapper(f, PhantomData)))
+    }
+
+    pub fn next(self) -> (bool, Self) {
+        // maybe change this
+# /*
+        self.0()
+# */ self.0.next()
+    }
+}
+
+fn test_covariance<'a: 'b, 'b>(e: BoolStream<'a>) -> BoolStream<'b> {
+    e
+}
+
+# use std::marker::PhantomData;
+# struct Wrapper<'a, F>(F, PhantomData<&'a ()>);
+# trait Next {
+# fn next<'t>(self: Box<Self>) -> (bool, BoolStream<'t>) where Self: 't;
+# }
+# impl<'a, F: 'a + FnOnce() -> (bool, BoolStream<'a>)> Next for Wrapper<'a, F> {
+# fn next<'t>(self: Box<Self>) -> (bool, BoolStream<'t>) where Self: 't { self.0() }
+# }
+
+/// Tests to check that behaviour stays the same.
+
+fn get_true<'a>() -> BoolStream<'a> {
+    BoolStream::new(|| (true, get_false()))
+}
+
+fn get_false<'a>() -> BoolStream<'a> {
+    BoolStream::new(|| (false, get_true()))
+}
+
+let e = get_true();
+let (x, e) = e.next();
+assert!(x);
+let (x, e) = e.next();
+assert!(!x);
+let (x, e) = e.next();
+assert!(x);
+let (x, e) = e.next();
+assert!(!x);
+test_covariance(e);
+```

src/exercises/multiple_blanket.md

@@ -1,9 +1,13 @@
 Make this compile.
-- `A1` doesn't know about/depend on `A2`
-- `A2` doesn't know about/depend on `A1`
-- `A1` doesn't know about/depend on `A`
-- `A2` doesn't know about/depend on `A`
-- can't edit definitions of `A`, `test`, `tes1`, `test2`; can only add code outside of those items
+- `A1` doesn't know about/depend on `A2`.
+- `A2` doesn't know about/depend on `A1`.
+- `A1` doesn't know about/depend on `A`.
+- `A2` doesn't know about/depend on `A`.
+- Some types are `A1` but not `A2`.
+- Some types are `A2` but not `A1`.
+- Some types are `A` but not `A2`.
+- Some types are `A` but not `A1`.
+- Can't edit definitions of `A`, `test`, `tes1`, `test2`; can only add code outside of those items.
 ```rust
 trait A {
     fn a_ref(&self) -> u64;

src/exercises/refbind.md

@@ -0,0 +1,26 @@
+```rust
+# mod __ {
+fn refbind<T, F: Fn(&T) -> Option<&T>>(f: F, fa: Option<&T>) -> Option<&T> {
+    match fa {
+        Some(a) => f(a),
+        None => None,
+    }
+}
+# }
+# fn refbind<'a,'b,T:'a+?Sized>(f:impl'a+Fn(&'a T)->Option<&'b T>,fa:Option<&'a T>)->Option<&'b T>{fa.and_then(f)}
+
+// don't change anything below
+
+let apple = "apple".to_string();
+let banana = "banana".to_string();
+assert_eq!(
+    refbind(|_: &String| Some(&banana), Some(&apple)),
+    Some(&banana)
+);
+
+let banana = "banana";
+assert_eq!(
+    refbind(|_: &str| Some(banana), Some("apple")),
+    Some(banana)
+);
+```

src/overview.md

@@ -21,10 +21,10 @@ Some exercises may not include have the replaced parts greyed out:
 ```rust
 # mod __ {
 fn fix_me() {
-# }
+}
 # }
 # fn fixed_name() {
-}
+# }
 
 fn do_not_change_this() {
     fixed_name()