Elizabeth Ryan lizzabees

Parsing in Unison Part 1: Combinator Combo

Come with me as I explore different approaches to parsing in Unison! I'm prone to getting a little too wordy and going on tangents, so I will do my best to keep this focused and concrete. If you're reading this, the odds are high that you're familiar with most of what I'll be covering. This is written as a Unison transcript, which is really neat! There will also be Haskell code and possibly some C at some point. I will assume you have some experience with all of that, as well as some knowledge and practice when it comes to parsing. One last thing before we get to work -- I am a professional novice and you should not take what I say as authoritative. If I say something incorrect or make mistakes (especially likely when I talk about any of the formal basis for this stuff), please reach out!

Parsec

Alright! Lets start with parser combinators! They're (deceptively) simple, powerful, well known, and ideal for a functional setting. I'm

	unique type ErrorItem is i
	= EOI
	\| Any
	\| One i
	\| Many is
	\| Named Text
	\| Not (ErrorItem is i)

	unique type ParseError e is i
	= Expected [(ErrorItem is i)] [(ErrorItem is i)]

	#!/usr/bin/env cabal
	{- cabal:
	build-depends: base ^>=4.14.3.0
	, parsec
	-}
	module Main where

	import Control.Monad (forever, unless)
	import Data.Functor ((<&>))
	import Data.List (intersperse)

	#include <stdint.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <string.h>

	typedef struct entry {
	char letter;
	int count;
	} entry;

	#!/usr/bin/env cargo-script script
	use std::collections::HashMap;
	use std::fs::File;
	use std::io::prelude::*;
	use std::io::{BufReader, Result};
	use std::iter;

	fn main() -> Result<()> {
	let fp = File::open("/usr/share/dict/words")?;
	let mut reader = BufReader::new(fp);

	#!/usr/bin/env cabal
	{- cabal:
	build-depends: base ^>=4.14.3.0
	, containers
	-}

	module Main where

	import Control.Monad.ST
	import Data.List (sortOn)