How to write the Visitor Pattern for Abstract Syntax Tree in Python?

Posted by bodacydo on Stack Overflow See other posts from Stack Overflow or by bodacydo
Published on 2010-03-26T18:14:07Z Indexed on 2010/03/26 18:23 UTC
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Filed under:

abstract-syntax-tree

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parsing

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visitor-pattern

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compiler

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python

My collegue suggested me to write a visitor pattern to navigate the AST. Can anyone tell me more how would I start writing it?

As far as I understand, each Node in AST would have visit() method (?) that would somehow get called (from where?). That about concludes my understanding.

To simplify everything, suppose I have nodes Root, Expression, Number, Op and the tree looks like this:

       Root
        |
       Op(+)
      /   \
     /     \
 Number(5)  \
             Op(*)
             /   \
            /     \
           /       \
       Number(2)   Number(444)

Can anyone think of how the visitor pattern would visit this tree to produce output:

 5 + 2 * 444

Thanks, Boda Cydo.

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