如何在 Squeak4.1 中解析文件中的字符？
朋友，假设我有一个文件test.txt，文件内容是“1+2*3”，如果直接在Squeak的工作区中表达公式，打印出来会结果9，我想要什么得到的是7 然后我从文件中读取文件内容1+2*3。像这样的代码，效果很好，
ReadFrom
"read the equation from ./formular.txt"
| fileContents |
fileContents := FileStream
readOnlyFileNamed: 'test.txt'
do: [:f | f contents ].
^fileContents.
但是如何将字符串“1+2*3”的5个字符存储到集合中，进一步我可以使用二叉树来计算方程？有人可以给我一些提示吗？首先谢谢:)
friend, suppose I have a file test.txt, the content of file is "1+2*3", if the fomular directly expressed in Squeak's Workspace, print it will result 9, What I want to get is 7
then I read the file content 1+2*3 from a file. code like this and it works well
ReadFrom
"read the equation from ./formular.txt"
| fileContents |
fileContents := FileStream
readOnlyFileNamed: 'test.txt'
do: [:f | f contents ].
^fileContents.
but how can I store the 5 caracters of string "1+2*3" into a collection , further I can use binary tree to calculate the equation? Do somebody can give me some hints? thanks first :)
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SmaCC 教程最终构建了几乎您想要的内容。
引用上述教程：
SmaCC 是一个成熟的 Smalltalk 解析器生成器，根据您的需要，它可能有点过头了。
如果您只想构建一个简单的计算器，您可以使用 Shunting-yard 算法 进行转换将数学表达式中缀到 RPN 中并轻松对其求值。
The SmaCC tutorial ends up building pretty much what you want.
Quote from said tutorial:
SmaCC is a full-blown parser generator for Smalltalk which may be overkill depending on your needs.
If you just want to build a simple calculator you can use the Shunting-yard algorithm to convert an infix mathematical expression into RPN and evaluate it easily.
也许在顶部添加运算符的优先级：
Maybe adding the precedence of the operators at the top: