boost::spirit, abstract syntax tree question

This is a discussion on boost::spirit, abstract syntax tree question within the C++ Programming forums, part of the General Programming Boards category; is there some trick to have an epsilon_p as a root_node? (using ast_parse) so id like this grammar to work: ...

  1. #1
    Registered User
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    Aug 2001
    Posts
    244

    boost::spirit, abstract syntax tree question

    is there some trick to have an epsilon_p as a root_node?

    (using ast_parse)

    so id like this grammar to work:
    Code:
    expression_0
    = expression_1 >> *(root_node_d[epsilon_p] >> expression_2) //!!! doesnt work
    ;
    
    expression_1
    = expression_2 >> *(
        (root_node_d[ch_p('+')] >> expression_2) // works perfectly
        (root_node_d[ch_p('-')] >> expression_2)
    );
    
    expression_2
    = identifier
    | value
    | inner_node_d['(' >> expression_0 >> ')']
    ;
    
    
    expression
    = expression_0
    ;


    unfortunately, there is no root node created for the rule expression_0.
    so instead of building the abstract syntax tree for
    "a b c d"
    as
    Code:
            []
           /  \d
          []
         /  \
       []    c
      /  \
    a   b
    the tree is built as:
    Code:
           []
    /    |     |     \
    a   b    c      d
    signature under construction

  2. #2
    l2u
    l2u is offline
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    May 2006
    Posts
    630
    Did you post on boost spirit newsgroup?

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