%whites =/([ \t]*(?:#.*)?)/ 
%token NUM =/([0-9]+(?:\.[0-9]+)?)/ 
%token VAR =/([A-Za-z][A-Za-z0-9_]*)/ 
%right '=' 
%left '-' '+' 
%left '*' '/' 
%left NEG 
%right '^' 

%%

start:
      input 
;
input:
      line * 
;
line:
      '\n'
    | exp '\n'
    | error '\n' 
;
exp:
      NUM
    | VAR
    | VAR '=' exp
    | exp '+' exp
    | exp '-' exp
    | exp '*' exp
    | exp '/' exp
    | '-' exp %prec NEG
    | exp '^' exp
    | '(' exp ')' 
;

%%