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POUnintentional concatenation in Bison/Yacc grammar
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  1. POUnintentional concatenation in Bison/Yacc grammar
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    copied!<p>I am experimenting with lex and yacc and have run into a strange issue, but I think it would be best to show you my code before detailing the issue. This is my lexer:</p> <pre><code>%{ #include &lt;stdlib.h&gt; #include &lt;string.h&gt; #include "y.tab.h" void yyerror(char *); %} %% [a-zA-Z]+ { yylval.strV = yytext; return ID; } [0-9]+ { yylval.intV = atoi(yytext); return INTEGER; } [\n] { return *yytext; } [ \t] ; . yyerror("invalid character"); %% int yywrap(void) { return 1; } </code></pre> <p>This is my parser:</p> <pre><code>%{ #include &lt;stdio.h&gt; int yydebug=1; void prompt(); void yyerror(char *); int yylex(void); %} %union { int intV; char *strV; } %token INTEGER ID %% program: program statement EOF { prompt(); } | program EOF { prompt(); } | { prompt(); } ; args: /* empty */ | args ID { printf(":%s ", $&lt;strV&gt;2); } ; statement: ID args { printf("%s", $&lt;strV&gt;1); } | INTEGER { printf("%d", $&lt;intV&gt;1); } ; EOF: '\n' %% void yyerror(char *s) { fprintf(stderr, "%s\n", s); } void prompt() { printf("&gt; "); } int main(void) { yyparse(); return 0; } </code></pre> <p>A very simple language, consisting of no more than strings and integer and a basic REPL. Now, you'll note in the parser that <em>args</em> are output with a leading colon, the intention being that, when combined with the first pattern of the rule of the <em>statement</em> the interaction with the REPL would look something like this:</p> <pre><code>&gt; aaa aa a :aa :a aaa&gt; </code></pre> <p>However, the interaction is this:</p> <pre><code>&gt; aaa aa a :aa :a aaa aa aa &gt; </code></pre> <p>Why does the token ID in the following rule</p> <pre><code>statement: ID args { printf("%s", $&lt;strV&gt;1); } | INTEGER { printf("%d", $&lt;intV&gt;1); } ; </code></pre> <p>have the semantic value of the total input string, newline included? How can my grammar be reworked so that the interaction I intended?</p>
 

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