The Perl Toolchain Summit needs more sponsors. If your company depends on Perl, please support this very important event.
%token NUM =/([0-9]+(?:\.[0-9]+)?)/ 
%token VAR =/([A-Za-z][A-Za-z0-9_]*)/ 
%right '=' 
%left '-' '+' 
%left '*' '/' 
%left NEG 
%tree

%%

line:
      exp  
;
exp:
      %name NUM
      NUM
    | %name VAR
      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 ')'  
;

%%