code.delx.au - gnu-emacs-elpa/blob - packages/wisi/wisi-compile.el

   1 ;; wisi-compile.el --- Grammar compiler for the wisi parser, integrating Wisi OpenToken output.  -*- lexical-binding:t -*-
   2 ;;
   3 ;; Copyright (C) 2012, 2013, 2015, 2016 Free Software Foundation, Inc.
   4 ;;
   5 ;; Author: Stephen Leake <stephen_leake@member.fsf.org>
   6 ;;
   7 ;; This file is part of GNU Emacs.
   8 ;;
   9 ;; GNU Emacs is free software: you can redistribute it and/or modify
  10 ;; it under the terms of the GNU General Public License as published by
  11 ;; the Free Software Foundation, either version 3 of the License, or
  12 ;; (at your option) any later version.
  13 ;;
  14 ;; GNU Emacs is distributed in the hope that it will be useful,
  15 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  16 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17 ;; GNU General Public License for more details.
  18 ;;
  19 ;; You should have received a copy of the GNU General Public License
  20 ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
  21 ;;
  22 ;;; History: first experimental version Jan 2013
  23 ;;
  24 ;;; Context
  25 ;;
  26 ;; Semantic (info "(semantic)Top") provides an LALR(1) parser
  27 ;; wisent-parse. The grammar used is defined by the functions
  28 ;; semantic-grammar-create-package, which reads a bison-like source
  29 ;; file and produces corresponding elisp source, and
  30 ;; wisent-compile-grammar, which generates a parser table.
  31 ;;
  32 ;; However, the algorithm used in wisent-compile-grammar cannot cope
  33 ;; with the grammar for the Ada language, because it is not
  34 ;; LALR(1). So we provide a generalized LALR parser, which spawns
  35 ;; parallel LALR parsers at each conflict. Instead of also rewriting
  36 ;; the entire semantic grammar compiler, we use the OpenToken LALR
  37 ;; parser generator, which is easier to modify (it is written in Ada,
  38 ;; not Lisp).
  39 ;;
  40 ;; The Ada function Wisi.Generate reads the bison-like input and
  41 ;; produces corresponding elisp source code, similar to that
  42 ;; produced by semantic-grammar-create-package.
  43 ;;
  44 ;; wisi-compile-grammar (provided here) generates the automaton
  45 ;; structure required by wisi-parse
  46 ;;
  47 ;;;;
  48
  49 (defun wisi-compose-action (value symbol-obarray nonterms)
  50   (let* ((nonterm (car value))
  51         (index   (cdr value))
  52         (symbol (intern-soft (format "%s:%d" nonterm index) symbol-obarray))
  53         (rhs (car (nth index (cdr (assoc nonterm nonterms))))))
  54     (list nonterm symbol (length rhs))
  55     ))
  56
  57 (defun wisi-replace-actions (action symbol-obarray nonterms)
  58   "Replace semantic action symbol names in ACTION with list as defined in `wisi-compile-grammar'.
  59 ACTION is the alist for one state from the grammar, with the form:
  60   ((default . error) ITEM ... )
  61 ITEM is one of:
  62 reduction  (TOKEN . (NONTERM . INDEX)) where NONTERM . INDEX gives the action symbol name.
  63 shift (TOKEN . STATE)
  64 shift/reduce conflict (STATE (NONTERM . INDEX))
  65 reduce/shift conflict ((NONTERM . INDEX) (NONTERM . INDEX))
  66
  67 SYMBOL-OBARRAY contains the action symbols.
  68 NONTERMS is from the grammar.
  69 Return the new action alist."
  70   ;; result is list of (nonterm index action-symbol token-count)
  71   (let (result item)
  72     (while action
  73      (setq item (pop action))
  74      (cond
  75       ((or
  76         (memq (cdr item) '(error accept))
  77         (numberp (cdr item))) ;; shift
  78        (push item result))
  79
  80       ((listp (cdr item))
  81        (let ((value (cdr item)))
  82          (cond
  83           ((symbolp (car value))
  84            ;; reduction
  85            (push (cons (car item)
  86                        (wisi-compose-action value symbol-obarray nonterms))
  87                  result))
  88
  89           ((integerp (car value))
  90            ;; shift/reduce conflict
  91            (push (cons (car item)
  92                        (list (car value)
  93                              (wisi-compose-action (cadr value) symbol-obarray nonterms)))
  94                  result))
  95
  96           (t ;; reduce/reduce conflict
  97            (push (cons (car item)
  98                        (list (wisi-compose-action (car value) symbol-obarray nonterms)
  99                              (wisi-compose-action (cadr value) symbol-obarray nonterms)))
 100                  result))
 101           )))
 102
 103       (t
 104        (error "unexpected '%s'; expected 'error, 'accept, numberp, stringp, listp" (cdr item)))
 105       ));; while/cond
 106
 107    (reverse result)))
 108
 109 (defun wisi-semantic-action (form nonterm iactn symbol-obarray)
 110   "Define an Elisp semantic action function for a production, interned in SYMBOL-OBARRAY.
 111 FORM is the body of the semantic action.
 112 NONTERM is the nonterminal left hand side.
 113 IACTN is the index of the production in the NTERM rule.
 114
 115 The semantic action function accepts two arguments;
 116 - $nterm      : the nonterminal
 117 - wisi-tokens : the list of tokens to be reduced.
 118
 119 It returns nil; it is called for the semantic side-effects only."
 120   ;; based on comp.el wisent-semantic-action
 121   (let* ((name (format "%s:%d" nonterm iactn))
 122          (action-symbol (intern name symbol-obarray)))
 123
 124     (fset action-symbol
 125           `(lambda ($nterm wisi-tokens)
 126              ,form
 127              nil))))
 128
 129 (defun wisi-compile-grammar (grammar)
 130   "Compile the LALR(1) GRAMMAR; return the automaton for wisi-parse.
 131 GRAMMAR is a list TERMINALS NONTERMS ACTIONS GOTOS, where:
 132
 133 TERMINALS is a list of terminal token symbols.
 134
 135 NONTERMS is a list of productions; each production is a
 136 list (nonterm (tokens semantic-action) ...) where `semantic-action' is
 137 any lisp form. The set of (tokens semantic-action) are the right hand
 138 sides; nonterm is the left hand side.
 139
 140 ACTIONS is an array indexed by parser state, of alists indexed by
 141 terminal tokens. The value of each item in the alists is one of:
 142
 143 'error
 144
 145 'accept
 146
 147 integer - shift; gives new state
 148
 149 '(nonterm . index) - reduce by nonterm production index.
 150
 151 '(integer (nonterm . index)) - a shift/reduce conflict
 152 '((nonterm . index) (nonterm . index)) - a reduce/reduce conflict
 153
 154 The first item in the alist must have the key 'default (not a
 155 terminal token); it is used when no other item matches the
 156 current token.
 157
 158 GOTOS is an array indexed by parser state, of alists giving the
 159 new state after a reduce for each nonterminal legal in that
 160 state.
 161
 162 The automaton is an array [parser-actions gotos symbol-obarray]:
 163
 164 - parser-actions is a copy of the input ACTIONS, with semantic
 165 actions replaced by a list (nonterm action-symbol token-count),
 166 where:
 167
 168 -- nonterm is a symbol from NONTERMS, and is the non-terminal to
 169 reduce to
 170
 171 -- token-count is the number of tokens in the reduction,
 172
 173 -- action-symbol is nil if there is no semantic action, or a
 174 symbol interned in symbol-obarray
 175
 176 - gotos is a copy of GOTOS.
 177
 178 - symbol-obarray is an obarray containing functions that
 179 implement the semantic action for each nonterminal; the function
 180 names have the format nonterm:index."
 181   ;; We store named symbols for semantic actions, not just lambda
 182   ;; functions, so we have a name for debug trace.
 183   ;;
 184   ;; FIXME: TERMINALS is not used. Eliminating it requires decoupling
 185   ;; from OpenToken; we'll do that in the move to FastToken.
 186   ;;
 187   ;; FIXME: eliminate use of semantic-lex-* in *-wy.el. Similarly
 188   ;; requires decoupling from OpenToken
 189   ;;
 190   ;; FIXME: can eliminate obarray? We don't need the obarray to
 191   ;; avoid garbage collection of the symbols; they are all referenced in the compiled grammar.
 192   ;; But each semantic action function has to be defined (and byte-compiled?) somewhere?
 193   ;;     currently actions are _not_ byte-compiled; wisi-compile-grammar is run at load time
 194   ;;     need 'eval-when-compile' to byte-compile them?
 195   ;;     can't byte-compile obarray?
 196
 197   (let ((defs (nth 1 grammar))
 198         (symbol-obarray (make-vector 13 0));; for parse actions
 199         def nonterm rhs-list rule
 200         semantic-action index)
 201
 202     (while defs
 203       (setq def      (car defs)
 204             defs     (cdr defs)
 205             nonterm  (car def)
 206             rhs-list (cdr def)
 207             index    0)
 208       (while rhs-list
 209         (setq rule            (car rhs-list)
 210               rhs-list        (cdr rhs-list)
 211               semantic-action (cadr rule))
 212
 213         (when semantic-action
 214           (wisi-semantic-action semantic-action nonterm index symbol-obarray))
 215
 216         (setq index (1+ index))
 217         ))
 218
 219     ;; replace semantic actions in ACTIONS with symbols from symbol-obarray
 220     (let ((nactions (length (nth 2 grammar)))
 221           (actions (nth 2 grammar))
 222           (i 0))
 223       (while (< i nactions)
 224         (aset actions i
 225               (wisi-replace-actions (aref actions i) symbol-obarray (nth 1 grammar)))
 226         (setq i (1+ i)))
 227       (vector
 228        actions
 229        (nth 3 grammar)
 230        symbol-obarray)
 231       )))
 232
 233 (provide 'wisi-compile)
 234
 235 ;;;; end of file