+---
+title: "Advent of Code 2023"
+output: html_document
+css: modest.css
+---
+Code to solve the [Advent of Code](http://adventofcode.com/2023/) puzzles. This year, I'm using the puzzles to develop my skills in [Haskell](https://wiki.haskell.org/Haskell). I'm writing up a [commentary on these puzzles and my solutions](https://work.njae.me.uk/tag/advent-of-code/) on my blog.
+
+[Learn you a Haskell](http://learnyouahaskell.com/chapters), [Introduction to Haskell 98](https://www.haskell.org/tutorial/index.html), and [Hackage](https://hackage.haskell.org/) are good resources.
+
+The [Cabal user guide](https://cabal.readthedocs.io/en/latest/index.html) and [How I Start: Haskell](http://howistart.org/posts/haskell/1/) are good sources of using the tools.
+
+# Toolchain
+
+Install Ghcup following [the instructions](https://www.haskell.org/ghcup/install/#installation), making sure to load the updated environment with
+
+```bash
+source /home/neil/.ghcup/env
+```
+
+and then set the default GHC to use with `ghcup set ghc 9.0.1` .
+
+Install [Haskell Language Server](https://haskell-language-server.readthedocs.io/en/latest/configuration.html) for Sublime Text
+
+
+## Creating the repository and project
+Create the repository as normal: create the project in Gitolite, clone it, and insert the `.gitignore` and `README.md` files.
+
+There's one package per day, with the code for each package in sub-directories of the root directory.
+
+Create the basic `cabal` project.
+
+```
+cabal init
+```
+
+Modify the `advent-of-code21.cabal` file as needed, such as updating the Cabal version and writing the `common` stanzas.
+
+## Creating subsequent days
+
+Each day lives in a separate directory, with code in the `src` directory.
+
+Compile with
+```
+cabal build
+```
+or
+```
+cabal build advent01
+```
+
+Run with
+```
+cabal run advent01
+```
+
+If you want to pass in additional RTS parameters, do it like this:
+```
+cabal run advent01 -- +RTS -K0 -RTS
+```
+
+Run interactively with
+```
+cabal repl advent01
+```
+or
+```
+stack ghci advent01:exe:advent01
+```
+if the first form is ambiguous.
+
+## Profiling
+
+To profile, use
+
+```
+cabal run advent01 --enable-profiling -- +RTS -N -p -s -hT
+```
+
+Or, you can simplify the RTS options by adding them to a new stanza in the cabal file:
+
+```
+executable advent01prof
+ import: common-extensions, build-directives
+ main-is: advent01/Main.hs
+ build-depends: text, containers, linear, array, pqueue, mtl, lens
+ ghc-options: -O2
+ -Wall
+ -threaded
+ -eventlog
+ -rtsopts "-with-rtsopts=-N -p -s -hT"
+```
+
+Only include the `-eventlog` directive if you want to use Threadscope to investigate parallel behaviour.
+
+then running
+
+```
+cabal run advent01prof --enable-profiling
+```
+
+
+Generate the profile graph with
+```
+hp2ps -M advent01.hp
+```
+
+
+# Packages
+
+Packages I used a lot:
+
+* [Containers](https://hackage.haskell.org/package/containers) (and some [better documentation](https://haskell-containers.readthedocs.io/en/latest/intro.html)); [Unordered containers](https://hackage.haskell.org/package/unordered-containers) is a mostly-equivalent alternative.
+* [Attoparsec](https://hackage.haskell.org/package/attoparsec) (and [Megaparsec](https://hackage.haskell.org/package/megaparsec), and [ReadP](https://hackage.haskell.org/package/base-4.14.1.0/docs/Text-ParserCombinators-ReadP.html) once).
+
+There are somewhat decent [tutorials on Megaparsec](https://markkarpov.com/tutorial/megaparsec.html) and [Attoparsec](https://www.schoolofhaskell.com/school/starting-with-haskell/libraries-and-frameworks/text-manipulation/attoparsec).
+
+Packages I didn't use much, but need to remember:
+
+* [Arithmoi](https://hackage.haskell.org/package/arithmoi) for number theory
+* [Pointed List](https://hackage.haskell.org/package/pointedlist-0.6.1) for zipper lists (sometimes circular)
+* [Vector](https://hackage.haskell.org/package/vector) for array-like things
+* [Linear](https://hackage.haskell.org/package/linear) for coordinate-vector like things
+* [Grid](https://hackage.haskell.org/package/grid) for 2-d grids
+* [Graph-wrapper](https://hackage.haskell.org/package/graph-wrapper) for graphs
+* [Lens](https://hackage.haskell.org/package/lens) (and a [summary of operators](https://github.com/ekmett/lens/wiki/Operators)). I didn't use these much this year, but did a lot last year.
+* [RWS](https://hackage.haskell.org/package/mtl-2.2.2/docs/Control-Monad-RWS-Lazy.html) (Reader-Writer-State monad stack); again, used a lot last year but not this year
+* [Monad loops](https://hackage.haskell.org/package/monad-loops-0.4.3/docs/Control-Monad-Loops.html), and [a description](https://conscientiousprogrammer.com/blog/2015/12/11/24-days-of-hackage-2015-day-11-monad-loops-avoiding-writing-recursive-functions-by-refactoring/)
+* [Replace-Megaparsec](https://github.com/jamesdbrock/replace-megaparsec), for using Mpc for all sorts of things traditionally done with regex substitutions.
+
+# Readme
+
+Build this readme file wth
+```
+pandoc -s README.md > README.html
+```
+
+(Using the [Modest style](https://github.com/markdowncss/modest).)