how to parse standard algebraic notation

Chris Angelico rosuav at gmail.com
Wed Oct 1 19:01:44 CEST 2014


On Thu, Oct 2, 2014 at 2:45 AM, Steven D'Aprano
<steve+comp.lang.python at pearwood.info> wrote:
> Code for evaluating mathematical expressions are very common, if you google
> for "expression parser" I am sure you will find many examples. Don't limit
> yourself to Python code, you can learn from code written in other languages
> too, e.g. I have a Pascal programming book that develops a parser for both
> polynomials and arithmetic expression.

Building expression evaluators is good fun! And then you can add
specialty terms, like dice rolling.

> roll 2d6 + d6 "Electric" + 12 "Strength"
[ROLL] Rosuav rolls 2d6: 3, 6, totalling 9.
[ROLL] Rosuav rolls d6: 1 ("Electric")
[ROLL] Rosuav adds a bonus of 12 ("Strength")
[ROLL] For 2d6 + d6 "Electric" + 12 "Strength", Rosuav totals: 22

The code behind that follows a fairly similar pattern to what you
describe, only it deals with dice rolls (NdM -> roll N dice with M
sides each) instead of powers of x. (And it allows comments/tags.)

ChrisA



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