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POHow to write flex and bison file parsing this language?
 

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  1. POHow to write flex and bison file parsing this language?
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    <p>Let's define a language:</p> <pre><code>VAR := [0-9A-Za-z_]+ Exp := VAR | VAR,'=',VAR | '(', Exp, ')' | Exp, '&amp;', Exp | Exp ,'|', Exp </code></pre> <p>eg: "( a = b ) &amp; ( c | (d=e) ) "is legal</p> <p>I've read the YASS &amp; Lex manual, but I'm totally confused , I just want the compiler that can parse this language <br/> Can you tell me how to write the flex&amp;bison configure file for this language?</p> <p>I've done so far:</p> <p>file a.l:</p> <pre><code>%{ #include &lt;string.h&gt; #include "stdlib.h" #include "stdio.h" #include "y.tab.h" %} %% ("&amp;"|"and"|"AND") { return AND; } ("|"|"or"|"OR") { return OR; } ("="|"eq"|"EQ") { return EQ; } ([A-Za-z0-9_]+) { return VAR;} ("(") { return LB ;} (")") { return RB ;} ("\n") { return LN ;} %% int main(void) { yyparse(); return 0; } int yywrap(void) { return 0; } int yyerror(void) { printf("Error\n"); exit(1); } </code></pre> <p>file a.y</p> <pre><code>%{ #include &lt;stdio.h&gt; %} %token AND OR EQ VAR LB RB LN %left AND OR %left EQ %% line : | exp LN{ printf("LN: %s",$1);} ; exp: VAR { printf("var:%s",$1);} | VAR EQ VAR { printf("var=:%s %s %s",$1,$2,$3);} | exp AND exp { printf("and :%s %s %s",$1,$2,$3);} | exp OR exp { printf("or :%s %s %s",$1,$2,$3);} | LB exp RB { printf("abstract :%s %s %s",$1,$2,$3);} ; </code></pre> <p>Now I edited file as Chris Dodd guided,it seems much better(at least the lex worked fine),but I get output like this:</p> <pre><code>disk_path&gt;myprogram a=b var=:(null) (null) (null)LN: (null)ab=b Error </code></pre> <p>So, why the function printf output null? and after input the second ,it prompt Error and exit the program?</p>
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    1. COShow us what you tried. I'll give a few hints in a response, but you really should show what you tried first
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      1. POHow to write flex and bison file parsing this language?
      1. USFoo Bah
 

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