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diff --git a/share/doc/psd/15.yacc/ssa b/share/doc/psd/15.yacc/ssa new file mode 100644 index 000000000000..17e815edfcb1 --- /dev/null +++ b/share/doc/psd/15.yacc/ssa @@ -0,0 +1,150 @@ +.\" Copyright (C) Caldera International Inc. 2001-2002. All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions are +.\" met: +.\" +.\" Redistributions of source code and documentation must retain the above +.\" copyright notice, this list of conditions and the following +.\" disclaimer. +.\" +.\" Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" +.\" All advertising materials mentioning features or use of this software +.\" must display the following acknowledgement: +.\" +.\" This product includes software developed or owned by Caldera +.\" International, Inc. Neither the name of Caldera International, Inc. +.\" nor the names of other contributors may be used to endorse or promote +.\" products derived from this software without specific prior written +.\" permission. +.\" +.\" USE OF THE SOFTWARE PROVIDED FOR UNDER THIS LICENSE BY CALDERA +.\" INTERNATIONAL, INC. AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR +.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED +.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE +.\" DISCLAIMED. IN NO EVENT SHALL CALDERA INTERNATIONAL, INC. BE LIABLE +.\" FOR ANY DIRECT, INDIRECT INCIDENTAL, SPECIAL, EXEMPLARY, OR +.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF +.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR +.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, +.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE +.\" OR OTHERWISE) RISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN +.\" IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. +.\" +.\" @(#)ssa 8.1 (Berkeley) 6/8/93 +.\" +.\" $FreeBSD$ +.SH +Appendix A: A Simple Example +.PP +This example gives the complete Yacc specification for a small desk calculator; +the desk calculator has 26 registers, labeled ``a'' through ``z'', and accepts +arithmetic expressions made up of the operators +, \-, *, /, +% (mod operator), & (bitwise and), | (bitwise or), and assignment. +If an expression at the top level is an assignment, the value is not +printed; otherwise it is. +As in C, an integer that begins with 0 (zero) is assumed to be octal; +otherwise, it is assumed to be decimal. +.PP +As an example of a Yacc specification, the desk calculator +does a reasonable job of showing how precedences and ambiguities +are used, and demonstrating simple error recovery. +The major oversimplifications are that the +lexical analysis phase is much simpler than for most applications, and the +output is produced immediately, line by line. +Note the way that decimal and octal integers are read in by the grammar rules; +This job is probably better done by the lexical analyzer. +.sp +.nf +.ta .5i 1i 1.5i 2i 2.5i + +%{ +# include <stdio.h> +# include <ctype.h> + +int regs[26]; +int base; + +%} + +%start list + +%token DIGIT LETTER + +%left \'|\' +%left \'&\' +%left \'+\' \'\-\' +%left \'*\' \'/\' \'%\' +%left UMINUS /* supplies precedence for unary minus */ + +%% /* beginning of rules section */ + +list : /* empty */ + | list stat \'\en\' + | list error \'\en\' + { yyerrok; } + ; + +stat : expr + { printf( "%d\en", $1 ); } + | LETTER \'=\' expr + { regs[$1] = $3; } + ; + +expr : \'(\' expr \')\' + { $$ = $2; } + | expr \'+\' expr + { $$ = $1 + $3; } + | expr \'\-\' expr + { $$ = $1 \- $3; } + | expr \'*\' expr + { $$ = $1 * $3; } + | expr \'/\' expr + { $$ = $1 / $3; } + | expr \'%\' expr + { $$ = $1 % $3; } + | expr \'&\' expr + { $$ = $1 & $3; } + | expr \'|\' expr + { $$ = $1 | $3; } + | \'\-\' expr %prec UMINUS + { $$ = \- $2; } + | LETTER + { $$ = regs[$1]; } + | number + ; + +number : DIGIT + { $$ = $1; base = ($1==0) ? 8 : 10; } + | number DIGIT + { $$ = base * $1 + $2; } + ; + +%% /* start of programs */ + +yylex() { /* lexical analysis routine */ + /* returns LETTER for a lower case letter, yylval = 0 through 25 */ + /* return DIGIT for a digit, yylval = 0 through 9 */ + /* all other characters are returned immediately */ + + int c; + + while( (c=getchar()) == \' \' ) { /* skip blanks */ } + + /* c is now nonblank */ + + if( islower( c ) ) { + yylval = c \- \'a\'; + return ( LETTER ); + } + if( isdigit( c ) ) { + yylval = c \- \'0\'; + return( DIGIT ); + } + return( c ); + } +.fi +.bp |