How to write simple parser for if and while statements?

Question

I need to write a simple parser that will convert the tokens to parser tree. I've already wrote LexicalAnalyzer that returns the tokens. Now, I want to write rules for "if and while" statements(for the beginning), so I could pass this rules to parser and it will create a tree. So i need to write the parser in the way, so I could write new rules.

Can you advise me how I can implement it in C#? Can you give me some example?

I read all kind pseudo, but have no idea how to start implement this. I saw the definition like a:b | c, c: terminal. If i understood this correctly, this means rules, but how to implement or maybe i am in wrong way — theateist, Sep 03 '11 at 16:22

score 4 · Accepted Answer · answered Sep 03 '11 at 16:14

4

In a recursive descent parser it's easy to implement these statements if you have the normal block and expression parsers. In pseudo-code, they are basically:

void ParseIf()
{
  Match("if");
  Match("(");
  ParseExpression();
  Match(")");
  ParseBlock();
}

and

void ParseWhile()
{
  Parse("while");
  Parse("(");
  ParseExpression();
  Parse(")");
  ParseBlock();
}

answered Sep 03 '11 at 16:14

Blindy

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Can you please specify what Match, MatchExpression,Parse, ParseBlock mean? – theateist Sep 03 '11 at 16:25
`Match` basically reads the token you give it and ignores it, it's to make sure it's there. The other two parse expressions and blocks respectively. – Blindy Sep 03 '11 at 16:25

How to write simple parser for if and while statements?

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