Merge pull request #1108 from maccoda/master

Return Result from main function.

Author: frewsxcv

src/error/result.md

@@ -45,6 +45,39 @@ unpleasant error message.
 To improve the quality of our error message, we should be more specific
 about the return type and consider explicitly handling the error.
 
+## Using `Result` in `main`
+
+The `Result` type can also be the return type of the `main` function if
+specified explicitly. Typically the `main` function will be of the form:
+
+```rust
+fn main() {
+    println!("Hello World!");
+}
+```
+
+However `main` is also able to have a return type of `Result`. If an error
+occurs within the `main` function it will return an error code and print a debug
+representation of the error (using the [`Debug`] trait). The following example
+shows such a scenario and touches on aspects covered in [the following section].
+
+```rust,editable
+use std::num::ParseIntError;
+
+fn main() -> Result<(), ParseIntError> {
+    let number_str = "10";
+    let number = match number_str.parse::<i32>() {
+        Ok(number)  => number,
+        Err(e) => return Err(e),
+    };
+    println!("{}", number);
+    Ok(())
+}
+```
+
+
 [option]: https://doc.rust-lang.org/std/option/enum.Option.html
 [result]: https://doc.rust-lang.org/std/result/enum.Result.html
 [parse]: https://doc.rust-lang.org/std/primitive.str.html#method.parse
+[`Debug`]: https://doc.rust-lang.org/std/fmt/trait.Debug.html
+[the following section]: error/result/early_returns.html