Taylor Fausak tfausak

Invertible syntax descriptions

An "invertible syntax description" is something that can be used to both parse and generate a syntax. For example, instead of defining separate toJson and fromJson functions for a given data type, an invertible syntax description could be used to provide both. There are many Haskell libraries that provide this functionality or something close to it. As far as I can tell most of them are at least inspired by Invertible syntax descriptions by Tillmann Rendel and Klaus Ostermann.

Personally I am interested in using these for HTTP routing. I frequently want to be able to define a route such as /episodes/:id.json, dispatch based on that route, and generate links to that route. Doing so manually is tedious and error prone.

	/.stack-work/
	/output/
	/results.csv
	/stack.yaml.lock

	-- I am working on a tool that downloads the Hackage index, stores it, and
	-- processes it. I am storing the index in PostgreSQL. I want to keep the
	-- maximum residency down. I don't care too much about total runtime.
	--
	-- This file contains a bunch of different operations in various formats. The
	-- idea is to get a baseline measurement for each operation (like downloading
	-- the index or reading it from a file) and each format (streaming, lazy, or
	-- strict). Those measurements can be used to create a minimum memory
	-- requirement for the actual tool.
	--

	-- Like Ratio but not broken.
	module Quotient
	( Quotient
	, quotient
	, unsafeQuotient
	, (%)
	, numerator
	, denominator
	, fromRatio
	, toRatio

	60,974,182,000 bytes allocated in the heap
	263,226,596,160 bytes copied during GC
	652,502,280 bytes maximum residency (815 sample(s))
	3,177,208 bytes maximum slop
	622 MB total memory in use (0 MB lost due to fragmentation)

	Tot time (elapsed) Avg pause Max pause
	Gen 0 57804 colls, 0 par 2.359s 2.372s 0.0000s 0.0006s
	Gen 1 815 colls, 0 par 245.031s 246.321s 0.3022s 0.6341s

	#!/usr/bin/env stack
	-- stack --resolver lts-13.0 script
	{-# OPTIONS_GHC -Weverything -Wno-implicit-prelude -Wno-unsafe #-}

	module Main ( main ) where

	import qualified Data.Aeson
	import qualified Data.Aeson.Types
	import qualified Data.List
	import qualified Data.Ord

	-- This whole thing is shamelessly stolen from:
	-- <https://doisinkidney.com/snippets/nary-uncurry.html>.

	-- Without flexible instances, GHC complains about the `HasApply` instances:
	--
	-- > Illegal instance declaration for `HasApply a Z`. All instance types must
	-- > be of the form `(T a1 ... an)` where `a1 ... an` are *distinct type
	-- > variables*, and each type variable appears at most once in the instance
	-- > head.
	--

	#!/usr/bin/env stack
	-- stack --resolver lts-12.10 script
	{-# OPTIONS_GHC -Weverything -Wno-unsafe -Wno-implicit-prelude #-}
	module Main ( main ) where
	import qualified Control.Concurrent as Concurrent
	import qualified Control.Monad as Monad
	import qualified Control.Monad.Catch as Catch
	import qualified Control.Monad.IO.Class as IO
	import qualified Data.Map as Map
	import qualified Data.Maybe as Maybe

	#!/usr/bin/env stack
	-- stack --resolver lts-10.0 script

	module Main
	( main
	)
	where

	import qualified Control.Monad as Monad
	import qualified Data.ByteString as ByteString

	replays/0ad2.replay Offline
	replays/000b.replay Private
	replays/1a12.replay Offline
	replays/1ae4.replay Offline
	replays/1bc2.replay Offline
	replays/1d1d.replay Offline
	replays/1ef9.replay Private
	replays/1f37.replay Offline
	replays/2cfe.replay Online
	replays/3abd.replay LAN