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wisent: Wisent Overview

 
 1 Wisent Overview
 *****************
 
 “Wisent” (the European Bison) is an implementation in Emacs Lisp of the
 GNU Compiler Compiler Bison.  Its code is a port of the C code of GNU
 Bison 1.28 & 1.31.
 
    For more details on the basic concepts for understanding Wisent, it
 is worthwhile to read the Bison Manual (bison)Top.
 
    Wisent can generate compilers compatible with the Semantic tool set.
 See the Semantic Manual (semantic)Top.
 
    It benefits from these Bison features:
 
    • It uses a fast but not so space-efficient encoding for the parse
      tables, described in Corbett’s PhD thesis from Berkeley:
           ‘Static Semantics in Compiler Error Recovery’
           June 1985, Report No.  UCB/CSD 85/251.
 
    • For generating the lookahead sets, Wisent uses the well-known
      technique of F. DeRemer and T. Pennello described in:
           ‘Efficient Computation of LALR(1) Look-Ahead Sets’
           October 1982, ACM TOPLAS Vol 4 No 4, 615–49,
           <http://dx.doi.org/10.1145/69622.357187>.
 
    • Wisent resolves shift/reduce conflicts using operator precedence
      and associativity.
 
    • Parser error recovery is accomplished using rules which match the
      special token ‘error’.
 
    Nevertheless there are some fundamental differences between Bison and
 Wisent.
 
    • Wisent is intended to be used in Emacs.  It reads and produces
      Emacs Lisp data structures.  All the additional code used in
      grammars is Emacs Lisp code.
 
    • Contrary to Bison, Wisent does not generate a parser which combines
      Emacs Lisp code and grammar constructs.  They exist separately.
      Wisent reads the grammar from a Lisp data structure and then
      generates grammar constructs as tables.  Afterward, the derived
      tables can be included and byte-compiled in separate Emacs Lisp
      files, and be used at a later time by the Wisent’s parser engine.
 
    • Wisent allows multiple start nonterminals and allows a call to the
      parsing function to be made for a particular start nonterminal.
      For example, this is particularly useful to parse a region of an
      Emacs buffer.  Semantic heavily depends on the availability of this
      feature.
 

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