comprehensive-rust/src/error-handling/exercise.md

---
minutes: 30
---

# Exercise: Rewriting with Result

The following implements a very simple parser for an expression language.
However, it handles errors by panicking. Rewrite it to instead use idiomatic
error handling and propagate errors to a return from `main`. Feel free to use
`thiserror` and `anyhow`.

HINT: start by fixing error handling in the `parse` function. Once that is
working correctly, update `Tokenizer` to implement
`Iterator<Item=Result<Token, TokenizerError>>` and handle that in the parser.

```rust,editable
{{#include exercise.rs:types}}

{{#include exercise.rs:panics}}
```
Comprehensive Rust v2 (#1073) I've taken some work by @fw-immunant and others on the new organization of the course and condensed it into a form amenable to a text editor and some computational analysis. You can see the inputs in `course.py` but the interesting bits are the output: `outline.md` and `slides.md`. The idea is to break the course into more, smaller segments with exercises at the ends and breaks in between. So `outline.md` lists the segments, their duration, and sums those durations up per-day. It shows we're about an hour too long right now! There are more details of the segments in `slides.md`, or you can see mostly the same stuff in `course.py`. This now contains all of the content from the v1 course, ensuring both that we've covered everything and that we'll have somewhere to redirect every page. Fixes #1082. Fixes #1465. --------- Co-authored-by: Nicole LeGare <dlegare.1001@gmail.com> Co-authored-by: Martin Geisler <mgeisler@google.com> 2023-11-29 10:39:24 -05:00			`---`
Tweak timings of exercises to better reflect teaching times (#1839) A few of the early exercises had much larger estimates than were actually necessary for the super simple early exercises. I've gone through and reviewed the time estimates for exercises and tweaked the estimates based on how much time students have actually needed in my classes so far. 2024-02-22 07:21:39 -08:00			`minutes: 30`
Comprehensive Rust v2 (#1073) I've taken some work by @fw-immunant and others on the new organization of the course and condensed it into a form amenable to a text editor and some computational analysis. You can see the inputs in `course.py` but the interesting bits are the output: `outline.md` and `slides.md`. The idea is to break the course into more, smaller segments with exercises at the ends and breaks in between. So `outline.md` lists the segments, their duration, and sums those durations up per-day. It shows we're about an hour too long right now! There are more details of the segments in `slides.md`, or you can see mostly the same stuff in `course.py`. This now contains all of the content from the v1 course, ensuring both that we've covered everything and that we'll have somewhere to redirect every page. Fixes #1082. Fixes #1465. --------- Co-authored-by: Nicole LeGare <dlegare.1001@gmail.com> Co-authored-by: Martin Geisler <mgeisler@google.com> 2023-11-29 10:39:24 -05:00			`---`

			`# Exercise: Rewriting with Result`

			`The following implements a very simple parser for an expression language.`
			`However, it handles errors by panicking. Rewrite it to instead use idiomatic`
			error handling and propagate errors to a return from `main`. Feel free to use
			`thiserror` and `anyhow`.

			HINT: start by fixing error handling in the `parse` function. Once that is
			working correctly, update `Tokenizer` to implement
			`Iterator<Item=Result<Token, TokenizerError>>` and handle that in the parser.

			```rust,editable
			`{{#include exercise.rs:types}}`

			`{{#include exercise.rs:panics}}`
			```