fb1-5.y

%{
# include <stdio.h>
%}

%token NUMBER
%token ADD SUB MUL DIV ABS
%token OP CP
%token EOL

%%

calclist:
 | calclist exp EOL { printf("= %d\n> ", $2); }
 | calclist EOL { printf("> "); }
 ;

exp: factor
 | exp ADD exp { $$ = $1 + $3; }
 | exp SUB factor { $$ = $1 - $3; }
 | exp ABS factor { $$ = $1 | $3; }
 ;

factor: term
 | factor MUL term { $$ = $1 * $3; }
 | factor DIV term { $$ = $1 / $3; }
 ;

term: NUMBER
 | ABS term { $$ = $2 >= 0? $2 : - $2; }
 | OP exp CP { $$ = $2; }
 ;

%%

main()
{
	printf("> ");
	yyparse();
}
yyerror(char *s)
{
	fprintf(stderr, "error: %s\n", s);
}