Info Catalog wisent: Grammar styles wisent: Bison style

wisent: Iterative style

 
 4.1.1 Iterative style
 ---------------------
 
 The “iterative style” is the preferred style to use with Semantic.  It
 relies on an iterative parser back-end mechanism which parses start
 nonterminals one at a time and automagically skips unexpected lexical
 tokens in input.
 
    Compared to rule-based iterative functions (Bison style),
 iterative parsers are better in that they can handle obscure errors more
 cleanly.
 
    Each start nonterminal must produces a “raw tag” by calling a
 ‘TAG’-like grammar macro with appropriate parameters.  See also 
 Start nonterminals.
 
    Then, each parsing iteration automatically translates a raw tag into
 “expanded tags”, updating the raw tag structure with internal properties
 and buffer related data.
 
    After parsing completes, it results in a tree of expanded tags.
 
    The following example is a snippet of the iterative style Java
 grammar provided in the Semantic distribution in the file
 ‘semantic/wisent/java-tags.wy’.
 
      ...
      ;; Alternate entry points
      ;;    - Needed by partial re-parse
      %start formal_parameter
      ...
      ;;    - Needed by EXPANDFULL clauses
      %start formal_parameters
      ...
 
      formal_parameter_list
        : PAREN_BLOCK
          (EXPANDFULL $1 formal_parameters)
        ;
 
      formal_parameters
        : LPAREN
          ()
        | RPAREN
          ()
        | formal_parameter COMMA
        | formal_parameter RPAREN
        ;
 
      formal_parameter
        : formal_parameter_modifier_opt type variable_declarator_id
          (VARIABLE-TAG $3 $2 nil :typemodifiers $1)
        ;
 
    It shows the use of the ‘EXPANDFULL’ grammar macro to parse a
 ‘PAREN_BLOCK’ which contains a ‘formal_parameter_list’.  ‘EXPANDFULL’
 tells to recursively parse ‘formal_parameters’ inside ‘PAREN_BLOCK’.
 The parser iterates until it digested all available input data inside
 the ‘PAREN_BLOCK’, trying to match any of the ‘formal_parameters’ rules:
 
    • ‘LPAREN’
 
    • ‘RPAREN’
 
    • ‘formal_parameter COMMA’
 
    • ‘formal_parameter RPAREN’
 
    At each iteration it will return a ‘formal_parameter’ raw tag, or
 ‘nil’ to skip unwanted (single ‘LPAREN’ or ‘RPAREN’ for example) or
 unexpected input data.  Those raw tags will be automatically expanded by
 the iterative back-end parser.
 

Info Catalog wisent: Grammar styles wisent: Bison style