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Advent of Code 2021 Day 16
https://adventofcode.com/2021/day/16 This is the hardest of the problems I have managed to solve. Some of the issues were: On the good side, Attoparsec can handle the non-context-free aspects (eg the functions packets0 and packets1). Almost every line of the solution can be linked back to the puzzle’s requirements – there is very little visible plumbing.…
Attribute Grammars with Monads
Attribute grammars evaluate recursive data structures where inherited attributes are passed from the root to the leaves, and synthesised attributes are calculated in the leaves and passed back to the root. In “Beginning Haskell” pp343-4 (Apress ISBN 978-1-4302-6250-3), Alejandro Serrano Mena briefly discusses implementing attribute grammars using the Reader and Writer monads. He does not…
Observations of Kirch’s comet 1680-81
The observations Newton used to calculate the orbit of Kirch’s comet can be found in the tables in http://www.newtonproject.ox.ac.uk/view/texts/diplomatic/NATP00301 page 491. Observations up to 5 February are by Flamsteed; later observations are by Newton. Different versions of these tables exist. This version is sufficient to demonstrate the calculation. I have not found the Newton Project’s…
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Great Wall 