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/**************************************************************************/
/* */
/* The Why platform for program certification */
/* Copyright (C) 2002-2008 */
/* Romain BARDOU */
/* Jean-Franois COUCHOT */
/* Mehdi DOGGUY */
/* Jean-Christophe FILLITRE */
/* Thierry HUBERT */
/* Claude MARCH */
/* Yannick MOY */
/* Christine PAULIN */
/* Yann RGIS-GIANAS */
/* Nicolas ROUSSET */
/* Xavier URBAIN */
/* */
/* This software is free software; you can redistribute it and/or */
/* modify it under the terms of the GNU General Public */
/* License version 2, as published by the Free Software Foundation. */
/* */
/* This software is distributed in the hope that it will be useful, */
/* but WITHOUT ANY WARRANTY; without even the implied warranty of */
/* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. */
/* */
/* See the GNU General Public License version 2 for more details */
/* (enclosed in the file GPL). */
/* */
/**************************************************************************/
/* LL parser */
/* grammar for arithmetic expressions:
E ::= T | T "+" E
E ::= F | F "*" T
F ::= "id" | "(" E ")"
*/
enum T { PLUS, MULT, LPAR, RPAR, ID, EOF };
typedef enum T token;
token *text; // should be ghost?
//@ ensures \result == *text
token next_token();
//@ ensures text == text+1
void advance();
/*@ requires 1 // TODO
@ ensures 0 // never returns
@*/
void parse_error();
/*@ requires 1 // TODO
@ ensures 0 // never returns
@*/
void success();
void parse_S();
void parse_E();
void parse_T();
void parse_F();
void parse_S() {
parse_E();
if (next_token() == EOF)
success();
else
parse_error();
}
void parse_E() {
parse_T();
switch (next_token()) {
case PLUS:
advance();
parse_E();
return;
default:
return;
}
}
void parse_T() {
parse_F();
switch (next_token()) {
case MULT:
advance();
parse_T();
return;
default:
return;
}
}
void parse_F() {
switch (next_token ()) {
case ID:
advance();
return;
case LPAR:
advance();
parse_E();
switch (next_token()) {
case RPAR:
advance();
return;
default:
parse_error();
}
default:
parse_error();
}
}
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