# [plt-scheme] rookie question

Hi:
I am developping a simple parser. When I run the parser by typing
(scan&parse "(* 2 6)")
I get the following error:
. parsing: at line 1: nonterminal <expression> can't begin with
literal-string25 "*"
The reason that above error occurs is that my parser tries to read
* as a symbol. But the grammar of proc-type-exp also need *, but it
treats * as a string. So scanner confuses. Now I know what causes the
error, but I do not know the solution. So can you give the solution to
me? The followings are my codes:
define the-lexical-spec
'((whitespace (whitespace)
skip)
(comment ("%" (arbno (not #\newline)))
skip)
(identifier ((or letter "_" "-" "?" "+" "-" "*") (arbno (or letter
digit "_" "-" "?" "+" "-" "*"))) symbol)
(number (digit (arbno digit))
number)))
(define the-grammar
'((program (expression) a-program)
(expression (number) lit-exp)
(expression ("true") true-exp)
(expression ("false") false-exp)
(expression (identifier) var-exp)
(expression
("if" expression "then" expression "else" expression)
if-exp)
(expression
("let" (arbno identifier "=" expression) "in" expression)
let-exp)
(expression
("proc" "(" (separated-list type-exp identifier ",") ")" expression)
proc-exp)
(expression
("(" expression (arbno expression) ")")
app-exp)
(type-exp ("int") int-type-exp)
(type-exp ("bool") bool-type-exp)
(type-exp
("(" (separated-list type-exp "*") "->" type-exp ")")
proc-type-exp)
))
(sllgen:make-define-datatypes the-lexical-spec the-grammar)
(define scan&parse
(sllgen:make-string-parser the-lexical-spec the-grammar))