all_errors

src/SUMMARY.md

@@ -12,6 +12,7 @@
 - [Chapter 2](./chapter_2.md)
   - [AnyStr](./exercises/anystr.md)
   - [Mode](./exercises/mode.md)
+  - [All Errors](./exercises/all_errors.md)
 - [Chapter 3](./chapter_3.md)
   - [Composition](./exercises/composition.md)
 

src/exercises/all_errors.md

@@ -0,0 +1,36 @@
+# Report all errors (or only the first error)
+
+```rust
+# trait Collects {
+# type Error;
+# type Output;
+# fn push(&self, trace: Vec<i32>, next: i32) -> Result<Vec<i32>, Self::Error>;
+# fn regularize(&self, result: Result<Result<Vec<i32>, Vec<i32>>, Self::Error>) -> Result<Vec<i32>, Self::Output>;
+# }
+# struct First;
+# struct All;
+# impl Collects for First {
+# type Error = i32;
+# type Output = i32;
+# fn push(&self, _trace: Vec<i32>, next: i32) -> Result<Vec<i32>, Self::Error> { Err(next) }
+# fn regularize(&self, result: Result<Result<Vec<i32>, Vec<i32>>, Self::Error>) -> Result<Vec<i32>, Self::Output> { result.map(|r| r.unwrap()) }
+# }
+# impl Collects for All {
+# type Error = std::convert::Infallible;
+# type Output = Vec<i32>;
+# fn push(&self, mut trace: Vec<i32>, next: i32) -> Result<Vec<i32>, Self::Error> { trace.push(next); Ok(trace) }
+# fn regularize(&self, result: Result<Result<Vec<i32>, Vec<i32>>, Self::Error>) -> Result<Vec<i32>, Self::Output> { result.unwrap() }
+# }
+# fn first() -> impl Collects<Output = i32> { First }
+# fn all() -> impl Collects<Output = Vec<i32>> { All }
+# fn _only_postivie<C: Collects>(numbers: Vec<i32>, c: &C) -> Result<Result<Vec<i32>, Vec<i32>>, C::Error> {
+# let mut state = Ok(vec![]);
+# for x in numbers { state = if x > 0 { state.map(|mut vec| {vec.push(x); vec}) } else { Err(c.push(match state { Ok(_) => vec![], Err(vec) => vec }, x)?) } }
+# Ok(state)
+# }
+# fn only_positive<C: Collects>(numbers: Vec<i32>, c: C) -> Result<Vec<i32>, C::Output> { c.regularize(_only_postivie(numbers, &c)) }
+assert_eq!(only_positive(vec![1, -1, 2, -4], first()), Err(-1));
+assert_eq!(only_positive(vec![1, 2, 3], first()), Ok(vec![1, 2, 3]));
+assert_eq!(only_positive(vec![1, -1, 2, -4], all()), Err(vec![-1, -4]));
+assert_eq!(only_positive(vec![1, 2, 3], all()), Ok(vec![1, 2, 3]));
+```