解析器和编译器的傻瓜。从哪里开始？ [英] Parsers and Compilers for Dummies. Where to start?
问题描述
这是一个很好的列表，但最好的一个在这个领域的一个完整的新手。一个来自较高级别背景的人（VB6，C＃，Java，Python） - 不熟悉C或C ++。我在这个阶段对手写解析和Lex / Yacc更感兴趣。
This is a good listing, but what is the best one for a complete newb in this area. One for someone coming from a higher level background (VB6,C#,Java,Python) - not to familiar with C or C++. I'm much more interested in hand-written parsing versus Lex/Yacc at this stage.
如果我只是主修计算机科学而不是心理学，我可能已经采取了类在这在大学。
If I had just majored in Computer Science instead of Psychology I might have taken a class on this in college. Oh well.
推荐答案
请查看：学习编写编译器
也很有趣：
- 如何编写程式设计语言
- 解析我在哪里可以了解it
- 学习资源解析器和编译器（确定你已经提到过这个。
- how to write a programming language
- parsing where can i learn about it
- learning resources on parsers interpreters and compilers (ok you already mentioned this one.
可以给出简短的介绍：
第一步是词法分析。字符流被翻译成令牌流，令牌可以是简单的，如==< = + - （etc），它们可以像标识符和数字一样复杂。如果你喜欢，我可以详细说明这一点。
The first step is the lexical analysis. A stream of characters is translated into a stream of tokens. Tokens can be simple like == <= + - (etc) and they can be complex like identifiers and numbers. If you like I can elaborate on this.
下一步是将令牌流翻译成语法树或其他表示。这被称为解析步骤。
The next step is to translate the tokenstream into a syntaxtree or an other representation. This is called the parsing step.
在创建解析器之前，您需要编写语法。例如，我们创建一个表达式解析器：
Before you can create a parser, you need to write the grammar. For example we create an expression parser:
令牌
addOp = '+' | '-';
mulOp = '*' | '/';
parLeft = '(';
parRight = ')';
number = digit, {digit};
digit = '0'..'9';
Each token can have different representations: + and = are both addOp and
23 6643 and 223322 are all numbers.
语言
exp = term | exp, addOp, term;
// an expression is a series of terms separated by addOps.
term = factor | term, mulOp, factor;
// a term is a series of factors separated by mulOps
factor = addOp, factor | parLeft, exp, parRight | number;
// a factor can be an addOp followed by another factor,
// an expression enclosed in parentheses or a number.
词典
我们创建一个状态引擎，遍历char流，创建一个令牌。
We create a state engine that walks through the char stream, creating a token
s00
'+', '-' -> s01 // if a + or - is found, read it and go to state s01.
'*', '/' -> s02
'(' -> s03
')' -> s04
'0'..'9' -> s05
whitespace -> ignore and retry // if a whitespace is found ignore it
else ERROR // sorry but we don't recognize this character in this state.
s01
found TOKEN addOp // ok we have found an addOp, stop reading and return token
s02
found TOKEN mulOp
s03
found TOKEN parLeft
s04
found TOKEN parRight
s05
'0'..'9' -> s05 // as long as we find digits, keep collecting them
else found number // last digit read, we have a number
解析器
现在是创建简单解析器/评估器的时候了。这是完整的代码。通常，它们是使用表创建的。但我们保持简单。读取标记并计算结果。
It is now time to create a simple parser/evaluator. This is complete in code. Normally they are created using tables. But we keep it simple. Read the tokens and calculate the result.
ParseExp
temp = ParseTerm // start by reading a term
while token = addOp do
// as long as we read an addop keep reading terms
if token('+') then temp = temp + ParseTerm // + so we add the term
if token('-') then temp = temp - ParseTerm // - so we subtract the term
od
return temp // we are done with the expression
ParseTerm
temp = ParseFactor
while token = mulOp do
if token('*') then temp = temp * ParseFactor
if token('/') then temp = temp / ParseFactor
od
return temp
ParseFactor
if token = addOp then
if token('-') then return - ParseFactor // yes we can have a lot of these
if token('+') then return ParseFactor
else if token = parLeft then
return ParseExpression
if not token = parRight then ERROR
else if token = number then
return EvaluateNumber // use magic to translate a string into a number
这是一个简单的例子。在实际示例中，您将看到错误处理是解析器的一个重要部分。
This was a simple example. In real examples you will see that error handling is a big part of the parser.
我希望这个澄清一点; - ）。
I hope this clarified a bit ;-).
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