%right '=' 
%left '-' '+' 
%left '*' '/' 
%left NEG 
%token NUM =
%token VAR =

%%

input:
    | input line  
;
line:
      '\n'
    | exp '\n'
    | exp ''  
;
exp:
      NUM
    | VAR
    | %name ASSIGN
      VAR '=' exp
    | %name PLUS
      exp '+' exp
    | %name MINUS
      exp '-' exp
    | %name TIMES
      exp '*' exp
    | %name DIV
      exp '/' exp
    | %name UMINUS
      '-' exp %prec NEG
    | '(' exp ')' 
;

%%