38e505c3e5
Add Caldera license. Approved by: David Taylor <davidt@caldera.com> Make roughly buildable under FreeBSD. The results are not perfect: the original Makefile referred to a refer file papers/Ind, which doesn't seem to have been kept, so the references to other publications are missing. In addition, the pagination is not correct, with the result that some .DS/.DE blocks leave large amounts of white space empty before them. Possibly this could be fixed by putting the (blank) footnotes at the end. PR: 35345 Requested by: Tony Finch <fanf@dotat.at>
151 lines
4.6 KiB
Plaintext
151 lines
4.6 KiB
Plaintext
.\" Copyright (C) Caldera International Inc. 2001-2002. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions are
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.\" met:
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.\"
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.\" Redistributions of source code and documentation must retain the above
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.\" copyright notice, this list of conditions and the following
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.\" disclaimer.
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.\"
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.\" Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\"
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.\" This product includes software developed or owned by Caldera
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.\" International, Inc. Neither the name of Caldera International, Inc.
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.\" nor the names of other contributors may be used to endorse or promote
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.\" products derived from this software without specific prior written
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.\" permission.
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.\"
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.\" USE OF THE SOFTWARE PROVIDED FOR UNDER THIS LICENSE BY CALDERA
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.\" INTERNATIONAL, INC. AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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.\" DISCLAIMED. IN NO EVENT SHALL CALDERA INTERNATIONAL, INC. BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
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.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
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.\" OR OTHERWISE) RISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
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.\" IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" @(#)ssa 8.1 (Berkeley) 6/8/93
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.\"
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.\" $FreeBSD$
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.SH
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Appendix A: A Simple Example
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.PP
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This example gives the complete Yacc specification for a small desk calculator;
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the desk calculator has 26 registers, labeled ``a'' through ``z'', and accepts
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arithmetic expressions made up of the operators +, \-, *, /,
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% (mod operator), & (bitwise and), | (bitwise or), and assignment.
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If an expression at the top level is an assignment, the value is not
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printed; otherwise it is.
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As in C, an integer that begins with 0 (zero) is assumed to be octal;
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otherwise, it is assumed to be decimal.
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.PP
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As an example of a Yacc specification, the desk calculator
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does a reasonable job of showing how precedences and ambiguities
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are used, and demonstrating simple error recovery.
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The major oversimplifications are that the
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lexical analysis phase is much simpler than for most applications, and the
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output is produced immediately, line by line.
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Note the way that decimal and octal integers are read in by the grammar rules;
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This job is probably better done by the lexical analyzer.
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.sp
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.nf
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.ta .5i 1i 1.5i 2i 2.5i
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%{
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# include <stdio.h>
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# include <ctype.h>
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int regs[26];
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int base;
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%}
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%start list
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%token DIGIT LETTER
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%left \'|\'
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%left \'&\'
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%left \'+\' \'\-\'
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%left \'*\' \'/\' \'%\'
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%left UMINUS /* supplies precedence for unary minus */
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%% /* beginning of rules section */
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list : /* empty */
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| list stat \'\en\'
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| list error \'\en\'
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{ yyerrok; }
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;
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stat : expr
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{ printf( "%d\en", $1 ); }
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| LETTER \'=\' expr
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{ regs[$1] = $3; }
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;
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expr : \'(\' expr \')\'
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{ $$ = $2; }
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| expr \'+\' expr
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{ $$ = $1 + $3; }
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| expr \'\-\' expr
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{ $$ = $1 \- $3; }
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| expr \'*\' expr
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{ $$ = $1 * $3; }
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| expr \'/\' expr
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{ $$ = $1 / $3; }
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| expr \'%\' expr
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{ $$ = $1 % $3; }
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| expr \'&\' expr
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{ $$ = $1 & $3; }
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| expr \'|\' expr
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{ $$ = $1 | $3; }
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| \'\-\' expr %prec UMINUS
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{ $$ = \- $2; }
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| LETTER
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{ $$ = regs[$1]; }
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| number
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;
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number : DIGIT
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{ $$ = $1; base = ($1==0) ? 8 : 10; }
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| number DIGIT
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{ $$ = base * $1 + $2; }
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;
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%% /* start of programs */
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yylex() { /* lexical analysis routine */
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/* returns LETTER for a lower case letter, yylval = 0 through 25 */
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/* return DIGIT for a digit, yylval = 0 through 9 */
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/* all other characters are returned immediately */
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int c;
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while( (c=getchar()) == \' \' ) { /* skip blanks */ }
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/* c is now nonblank */
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if( islower( c ) ) {
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yylval = c \- \'a\';
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return ( LETTER );
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}
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if( isdigit( c ) ) {
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yylval = c \- \'0\';
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return( DIGIT );
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}
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return( c );
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}
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.fi
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.bp
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