help with simple grammar please

[Bernd Prager]

Hi,

 

just starting with bison and try to understand it.

The grammar file looks like:

------ test.y ---------------------

%{
#include <stdio.h>
#define YYERROR_VERBOSE
%}

 

%token WORD

%%

 

_expression_: word
        {  printf( "_expression_: (single word >%s<)\n", $1); }
    |       sentence
        {  printf ("_expression_: (sentence >%s<)\n", $1); }
    ;

 

/* a single word */
word:       WORD
        { printf( "word: >%s<\n", $1); }
    ;

 

sentence:   '(' word _expression_ ')'
        {  printf( "sentence: (word >%s< _expression_ >%s<)\n", $1, $2); }
    ;

 

%%
int main()
{
  {
    return(yyparse());
  }
}

 

int
yyerror (char *s)
{
  fprintf (stderr, "%s\n", s);
  return 1;
}

------ test.y ---------------------

 

The input line "echo "(one two)" | ./test " returns:

-------- snip --------------------

word: >one<
word: >two<
_expression_: (single word >two<)
sentence: (word >(null)< _expression_ >one two)<)
_expression_: (sentence >(null)<)

-------- snip --------------------

 

I was expecting something like:

-------- snip --------------------

word: >one<
_expression_: (single word >one<)
word: >two<
_expression_: (single word >two<)
sentence: (word >one< _expression_ >two<)
_expression_ (sentence >(one two)<)

-------- snip --------------------

 

I don't understand this. Where is my error in reasoning?

Can anybody help me?

Thanks,

-- B.