When trying to parse the simple input file

dog cat
one two

I want to be able to read (dog,cat) (one,two) and thought that I could do
that in the line: rule of my grammar. However for some reason $1 is
concatentated with $2:

scan: |dog|
scan: |cat|
gram: |dog cat| !cat!
scan: |one|
scan: |two|
gram: |one two| !two!

This probably has something to do with the fact that my yylval's are char *
not int, but I thought I had to actively $$=$1+' '+$2 for the behaviour I'm
seeing. Is this a bug, or my misunderstanding?

Cheers,

Patrick

To try it at home:

Makefile:

PROG=lexprob
SRCS=lexprob.c gram.y scan.l
NOMAN=noman
CFLAGS+=-g
LDADD+=-ll
YHEADER=yes
.include <bsd.prog.mk>

scan.l:

%{
#include "gram.h"
char *yylval;
%}
%%
[a-zA-Z]{3}	{
		  yylval=yytext;
		  printf("scan: |%s|\n",yylval);
		  return TLA;
		}
[ \t\n\r]	/* eat up whitespace */
%%
void yyerror(const char *errmsg)
{ 
  errx(1,"parser: %s at or near \"%s\"",errmsg,yytext);
}

gram.y:

%{
#include <stdio.h>
#define YYSTYPE char *
void yyerror(const char *);
%}
%token TLA
%%
input:	/* empty */
	| input line
	;
line:	TLA TLA	{printf("gram: |%s| !%s!\n",$1,$2);}
	;

lexprob.c:

#include <err.h>
#include <stdio.h>
#include <stdlib.h>

FILE *yyin;
int yyparse(void);

int main()
{
  if(yyin=fopen("lex.in","r"),yyin==(FILE *)NULL)
    errx(1,"Cannot open file \"lex.in\" for reading\n");
  yyparse();

  return 0;
}

lex.in:

dog cat
one two