Having hit rock bottom with an ‘I can’t understand my own code sufficiently enough to extend/maintain it’, I have been on a journey to review the perl5 Physics::Unit design and to use this to cut through my self made mess of raku Physics::Unit version 0.0.2.
Now I bring the perspective of a couple of years of regular raku coding to bear, so I am hoping that the bastard child of mature perl5 and raku version one will surpass both in the spirit of David Bowie’s “Pretty Things”.
One of the reasons I chose Physics::Units as a project was that, on the face of it, it seemed to have an aspect that could be approached by raku Grammars – helping me learn them. Here’s a sample of the perl5 version:
Yes – a recursive descent parser written from scratch in perl5 – pay dirt ! There are 215 source code lines dedicated to the parse function. 5 more screens like this…
So I took out my newly sharpened raku tools and here’s my entire port:
Instead of ranging over 215 lines, raku has refined this down to a total of 58 lines (incl. the 11 blank ones I kept in for readability) – that’s a space saving of over 70%. Partly removal of parser boilerplate code, partly the raku Grammar constructs and partly an increased focus on the program logic as opposed to the mechanism.
For my coding style, this represents a greater than a two-thirds improvement – by getting the whole parser onto a single screen, I find that I can get the whole problem into my brain’s working memory and avoid burning cycles scrolling up and down to pin down butterflies bugs.
Attentive students will have noted that the Grammar / code integration provides a very natural paradigm for loading real-world data into an OO system, the UnitAction class starts with a stub object and populates ‘has’ attributes as it goes.
Oh and the raku code does a whole lot more such as support for unicode superscripts (up to +/-4), type assignment and type checking, offsets (such as 0 K = 273.15 °C), wider tolerance of user input and so on. Most importantly Real values are kept as Rats as much as possible which helps greatly for example, when round tripping 38.5 °C to °F and back it is still equals 38.5 °C!
One final remark – use Grammar::Tracer is a fantastic debugging tool for finding and fixing the subtle bugs that can come in and contributing to quickly getting to the optimum solution.
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算法与数据结构(第二版)
傅清祥、王晓东 / 电子工业出版社 / 2001-8-1 / 34.00
本书是《计算机学科教学计划1993》的配套教材之一。它覆盖了《计算机学科教学计划1993》中开列的关于算法与数据结构主科目的所有知识单元。其主要内容有:算法与数据结构的概念、抽象数据类型(ADT)、基于序列的ADT(如表,栈,队列和串等)。反映层次关系的ADT(如树,堆和各种平衡树等)、关于集合的ADT(如字典,优先队列和共查集等)、算法设计的策略与技巧、排序与选择算法、图的算法、问题的计算复杂性一起来看看 《算法与数据结构(第二版)》 这本书的介绍吧!