扩展数学表达式(扩展括号) [英] Expanding math expression (expanding parentheses)

问题描述

我有一个像这样的表达式a*(b+c)，并且我已经成功解析为AST，所以它最终变成了:

I have a expression like this a*(b+c) and I have successfully parsed into an AST so it finally becomes:

我正在尝试扩展它最终变成的表达式 a*b + a*c，但没有运气.

I'm trying to expand the expression it finally becomes a*b + a*c, but with no luck.

我想知道一种扩展表达式的算法，或者也许是一个库来实现，最好是.NET.

I would like to know an algorithm to expand the expression, or maybe a library to do it, preferably for .NET.

推荐答案

这是prolog中的单行程序. 作为奖励，它可以双向工作. 也就是说，您将其设计为展开"，即可免费获得展开".这是一个使用yap prolog的交互式REPL的示例.都是大写字母的标识符是变量.

This is a one-line program in prolog . And as a bonus , it works both ways . i.e. you design it to "expand" , you get "unexpand" for free . Here is an example that uses the interactive REPL of yap prolog . The identifiers that are all capital letters are the variables .

$ yap
YAP 6.2.2 (x86_64-linux): Sat Sep 17 13:59:03 UTC 2016

?- [user].

/* consulting user_input... */

rewrite(A * (B + C), (A * B + A * C)) .

end_of_file .

/* example usage from the REPL */

?- rewrite(3 * (4 + 5), REWRITTEN) .

REWRITTEN = 3*4+3*5

?- rewrite(a * (b + c), REWRITTEN) .

REWRITTEN = a*b+a*c

/* example usage showing it work the opposite way */

?- rewrite(REWRITABLE,(3*4+3*5)) .

REWRITABLE = 3*(4+5)

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