scheme-字符串附加错误的类型以应用错误

Question

I have this code

(lambda (symbol)
  (let*(
        (datalist (get-list symbol))
    (desc " ")
        (html "<table border=\"1\">")
        (html (string-append html "<tr><td>" (list-ref datalist 1) "</td><t\
r><td>" (list-ref datalist  2) "</td></tr>"))
        )
    (do ((p 7 (+ 7 p)))
    ((> p (-(length datalist) 2)))
      (desc (string-append desc "<tr><td>"(list-ref datalist p) "</td><td>"\
 (list-ref datalist (+ p 1))"</td></tr>"))
      )
    (set! html (string-append html desc "</table>"))
      html
    )
  )

I'm basically taking some elements from a datalist and adding some html tags to them. However, when I run the code, I get a "wrong type to apply error" on the desc binding (line 4). What gives? Even when i change it to values such as "foo", i still get the wrong type error.

Any suggestions?

Answer 1

The error is not in the binding, is in the loop's body:

(desc (string-append desc …))

You're trying to apply desc as if it were a procedure - but it's a string. So basically that part of the code is doing something equivalent to this:

("s1" "s2")

Which will result in the reported error. Perhaps you meant to do this?

(set! desc (string-append desc …))

I'll take a guess to figure out what were you trying to implement. And do notice how properly indenting and formatting the code helps to make it clear:

(lambda (symbol)
  (let* ((desc " ")
         (datalist (get-list symbol))
         (html (string-append "<table border=\"1\">"
                              "<tr><td>"
                              (list-ref datalist 1)
                              "</td><tr><td>"
                              (list-ref datalist  2)
                              "</td></tr>")))
    (do ((p 7 (+ 7 p)))
      ((> p (- (length datalist) 2)))
      (set! desc (string-append desc 
                                "<tr><td>"
                                (list-ref datalist p) 
                                "</td><td>"
                                (list-ref datalist (+ p 1))
                                "</td></tr>")))
    (string-append html desc "</table>")))