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blog(aoc-2022): add initro
Signed-off-by: Matej Focko <mfocko@redhat.com>
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blog/aoc-2022/00-intro.md
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blog/aoc-2022/00-intro.md
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---
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title: Advent of Code '22 in Rust
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description: Preparing for Advent of Code '22.
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date: 2022-12-14T21:45
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slug: aoc-2022/intro
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authors:
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- name: Matej Focko
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title: "a.k.a. @mf"
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url: https://gitlab.com/mfocko
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image_url: https://github.com/mfocko.png
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tags:
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- aoc-2022
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- advent-of-code
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- rust
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hide_table_of_contents: false
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---
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Let's talk about the preparations for this year's [_Advent of Code_].
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<!--truncate-->
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## Choosing a language
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When choosing a language for AoC, you usually want a language that gives you a
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quick feedback which allows you to iterate quickly to the solution of the puzzle.
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One of the most common choices is Python, many people also use JavaScript or Ruby.
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Given the competitive nature of the AoC and popularity among competitive programming,
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C++ might be also a very good choice. Only if you are familiar with it, I guess…
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If you want a challenge, you might also choose to rotate the languages each day.
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Though I prefer to use only one language.
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For this year I have been deciding between _Rust_, _C++_ and _Pascal_ or _Ada_.
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I have tried Rust last year and have survived with it for 3 days and then gave
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up and switched to _Kotlin_, which was pretty good given it is „Java undercover“.
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I pretty much like the ideas behind Rust, I am not sure about the whole cult and
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implementation of those ideas though. After some years with C/C++, I would say
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that Rust feels _too safe_ for my taste and tries to „_punish me_“ even for the
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most trivial things.
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C++ is a very robust, but also comes with a wide variety of options providing you
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the ability to shoot yourself in the leg. I have tried to solve few days of previous
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Advent of Code events, it was _relatively easy_ to solve the problems in C++, given
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that I do not admit writing my own iterator for `enumerate`…
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Pascal or Ada were meme choices :) Ada is heavily inspired by Pascal and has a
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pretty nice standard library that offers enough to be able to quickly solve some
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problems in it. However the toolkit is questionable :/
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## Choosing libraries
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## Preparations for Rust
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All of the sources, later on including solutions, can be found at my
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[GitLab].
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### Toolkit
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Since we are using Rust, we are going to use a [Cargo] and more than likely VSCode
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with [`rust-analyzer`]. Because of my choice of libraries, we will also introduce
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a `.envrc` file that can be used by [`direnv`], which allows you to set specific
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environment variables when you enter a directory. In our case, we will use
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```bash
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# to show nice backtrace when using the color-eyre
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export RUST_BACKTRACE=1
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# to catch logs generated by tracing
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export RUST_LOG=trace
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```
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And for the one of the most obnoxious things ever, we will use a script to download
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the inputs instead of „_clicking, opening and copying to a file_“[^1]. There is
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no need to be _fancy_, so we will adjust Python script by Martin[^2].
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```py
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#!/usr/bin/env python3
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import datetime
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import yaml
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import requests
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import sys
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def load_config():
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with open("env.yaml", "r") as f:
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js = yaml.load(f, Loader=yaml.Loader)
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return js["session"], js["year"]
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def get_input(session, year, day):
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return requests.get(
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f"https://adventofcode.com/{year}/day/{day}/input",
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cookies={"session": session},
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headers={
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"User-Agent": "{repo} by {mail}".format(
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repo="gitlab.com/mfocko/advent-of-code-2022",
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mail="me@mfocko.xyz",
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)
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},
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).content.decode("utf-8")
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def main():
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day = datetime.datetime.now().day
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if len(sys.argv) == 2:
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day = sys.argv[1]
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session, year = load_config()
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problem_input = get_input(session, year, day)
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with open(f"./inputs/day{day:>02}.txt", "w") as f:
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f.write(problem_input)
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if __name__ == "__main__":
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main()
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```
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If the script is called without any arguments, it will deduce the day from the
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system, so we do not need to change the day every morning. It also requires a
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configuration file:
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```yaml
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# env.yaml
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session: ‹your session cookie›
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year: 2022
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```
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### Libraries
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Looking at the list of the libraries, I have chosen „a lot“ of them. Let's walk
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through each of them.
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[`tracing`] and [`tracing-subscriber`] are the crates that can be used for tracing
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and logging of your Rust programs, there are also other crates that can help you
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with providing backtrace to the Sentry in case you have deployed your application
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somewhere and you want to watch over it. In our use case we will just utilize the
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macros for debugging in the terminal.
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[`thiserror`], [`anyhow`] and [`color-eyre`] are used for error reporting.
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`thiserror` is a very good choice for libraries, cause it extends the `Error`
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from the `std` and allows you to create more convenient error types. Next is
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`anyhow` which kinda builds on top of the `thiserror` and provides you with simpler
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error handling in binaries[^3]. And finally we have `color-eyre` which, as I found
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out later, is a colorful (_wink wink_) extension of `eyre` which is fork of `anyhow`
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while supporting customized reports.
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In the end I have decided to remove `thiserror` and `anyhow`, since first one is
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suitable for libraries and the latter was basically fully replaced by `{color-,}eyre`.
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[`regex`] and [`lazy_static`] are a very good and also, I hope, self-explanatory
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combination. `lazy_static` allows you to have static variables that must be initialized
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during runtime.
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[`itertools`] provides some nice extensions to the iterators from the `std`.
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### My own „library“
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When creating the crate for this year's Advent of Code, I have chosen a library
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type. Even though standard library is huge, some things might not be included and
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also we can follow _KISS_. I have 2 modules that my „library“ exports, one for
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parsing and one for 2D vector (that gets used quite often during Advent of Code).
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Key part is, of course, processing the input and my library exports following
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functions that get used a lot:
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```rust
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/// Reads file to the string.
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pub fn file_to_string<P: AsRef<Path>>(pathname: P) -> String;
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/// Reads file and returns it as a vector of characters.
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pub fn file_to_chars<P: AsRef<Path>>(pathname: P) -> Vec<char>;
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/// Reads file and returns a vector of parsed structures. Expects each structure
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/// on its own line in the file. And `T` needs to implement `FromStr` trait.
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pub fn file_to_structs<P: AsRef<Path>, T: FromStr>(pathname: P) -> Vec<T>
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where
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<T as FromStr>::Err: Debug;
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/// Converts iterator over strings to a vector of parsed structures. `T` needs
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/// to implement `FromStr` trait and its error must derive `Debug` trait.
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pub fn strings_to_structs<T: FromStr, U>(
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iter: impl Iterator<Item = U>
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) -> Vec<T>
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where
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<T as std::str::FromStr>::Err: std::fmt::Debug,
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U: Deref<Target = str>;
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/// Reads file and returns it as a vector of its lines.
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pub fn file_to_lines<P: AsRef<Path>>(pathname: P) -> Vec<String>;
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```
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As for the vector, I went with a rather simple implementation that allows only
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addition of the vectors for now and accessing the elements via functions `x()`
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and `y()`. Also the vector is generic, so we can use it with any numeric type we
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need.
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### Skeleton
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We can also prepare a template to quickly bootstrap each of the days. We know
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that each puzzle has 2 parts, which means that we can start with 2 functions that
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will solve them.
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```rust
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fn part1(input: &Input) -> Output {
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todo!()
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}
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fn part2(input: &Input) -> Output {
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todo!()
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}
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```
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Both functions take reference to the input and return some output (in majority
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of puzzles, it is the same type). `todo!()` can be used as a nice placeholder,
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it also causes a panic when reached and we could also provide some string with
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an explanation, e.g. `todo!("part 1")`. We have not given functions a specific
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type and to avoid as much copy-paste as possible, we will introduce type aliases.
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```rust
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type Input = String;
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type Output = i32;
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```
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:::tip
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This allows us to quickly adjust the types only in one place without the need to
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do _regex-replace_ or replace them manually.
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:::
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For each day we get a personalized input that is provided as a text file. Almost
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all the time, we would like to get some structured type out of that input, and
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therefore it makes sense to introduce a new function that will provide the parsing
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of the input.
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```rust
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fn parse_input(path: &str) -> Input {
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todo!()
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}
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```
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This „parser“ will take a path to the file, just in case we would like to run the
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sample instead of input.
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OK, so now we can write a `main` function that will take all of the pieces and
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run them.
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```rust
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fn main() {
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let input = parse_input("inputs/dayXX.txt");
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println!("Part 1: {}", part_1(&input));
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println!("Part 2: {}", part_2(&input));
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}
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```
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This would definitely do :) But we have installed a few libraries and we want to
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use them. In this part we are going to utilize _[`tracing`]_ (for tracing, duh…)
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and _[`color-eyre`]_ (for better error reporting, e.g. from parsing).
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```rust
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fn main() -> Result<()> {
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tracing_subscriber::fmt()
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.with_env_filter(EnvFilter::from_default_env())
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.with_target(false)
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.with_file(true)
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.with_line_number(true)
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.without_time()
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.compact()
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.init();
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color_eyre::install()?;
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let input = parse_input("inputs/dayXX.txt");
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info!("Part 1: {}", part_1(&input));
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info!("Part 2: {}", part_2(&input));
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Ok(())
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}
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```
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The first statement will set up tracing and configure it to print out the logs to
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terminal, based on the environment variable. We also change the formatting a bit,
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since we do not need all the _fancy_ features of the logger. Pure initialization
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would get us logs like this:
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```
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2022-12-11T19:53:19.975343Z INFO day01: Part 1: 0
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```
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However after running that command, we will get the following:
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```
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INFO src/bin/day01.rs:35: Part 1: 0
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```
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And the `color_eyre::install()?` is quite straightforward. We just initialize the
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error reporting by _color eyre_.
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:::caution
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Notice that we had to add `Ok(())` to the end of the function and adjust the
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return type of the `main` to `Result<()>`. It is caused by the _color eyre_ that
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can be installed only once and therefore it can fail, that is how we got the `?`
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at the end of the `::install` which _unwraps_ the **»result«** of the installation.
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:::
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Overall we will get to a template like this:
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```rust
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use aoc_2022::*;
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use color_eyre::eyre::Result;
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use tracing::info;
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use tracing_subscriber::EnvFilter;
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type Input = String;
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type Output = i32;
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fn parse_input(path: &str) -> Input {
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todo!()
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}
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fn part1(input: &Input) -> Output {
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todo!()
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}
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fn part2(input: &Input) -> Output {
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todo!()
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}
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fn main() -> Result<()> {
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tracing_subscriber::fmt()
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.with_env_filter(EnvFilter::from_default_env())
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.with_target(false)
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.with_file(true)
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.with_line_number(true)
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.without_time()
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.compact()
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.init();
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color_eyre::install()?;
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let input = parse_input("inputs/dayXX.txt");
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info!("Part 1: {}", part_1(&input));
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info!("Part 2: {}", part_2(&input));
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Ok(())
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}
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```
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[^1]: Copy-pasting might be a relaxing thing to do, but you can also discover
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nasty stuff about your PC. See [this Reddit post and the comment].
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[^2]: [GitHub profile](https://github.com/martinjonas)
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[^3]: Even though you can use it even for libraries, but handling errors from
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libraries using `anyhow` is nasty… You will be the stinky one ;)
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[_Advent of Code_]: https://adventofcode.com
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[GitLab]: https://gitlab.com/mfocko/advent-of-code-2022
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[Cargo]: https://doc.rust-lang.org/cargo/
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[`rust-analyzer`]: https://rust-analyzer.github.io/
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[`direnv`]: https://direnv.net/
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[`tracing`]: https://crates.io/crates/tracing
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[`tracing-subscriber`]: https://crates.io/crates/tracing-subscriber
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[`thiserror`]: https://crates.io/crates/thiserror
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[`anyhow`]: https://crates.io/crates/anyhow
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[`color-eyre`]: https://crates.io/crates/color-eyre
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[`regex`]: https://crates.io/crates/regex
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[`lazy_static`]: https://crates.io/crates/lazy_static
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[`itertools`]: https://crates.io/crates/itertools
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[this Reddit post and the comment]: https://www.reddit.com/r/adventofcode/comments/zb98pn/comment/iyq0ono
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