[absrnd]

In a functional language (like Scheme) strings are immutable, so they are fixed size.

[kbp]

> In a functional language (like Scheme) strings are immutable, so they are fixed size.

Strings are mutable in standard Scheme (unlike, say, Java):

    #;1> (let ((string (string-copy "foo")))
           (string-set! string 0 #\b)
           string)
    "boo"

They're still a fixed length (as they are in virtually every language) because the only way to add onto them is to allocate a new string and copy everything over (this might be hidden behind a method, and you can avoid actually doing this every time by initially allocating more space than you need and using a fill pointer, but they're still fundamentally a fixed length). For example, the 4th edition of the Scheme Programming Language[0] gives this example definition of string-append:

    (define string-append
      (lambda args
        (let f ([ls args] [n 0])
          (if (null? ls)
              (make-string n)
              (let* ([s1 (car ls)]
                     [m (string-length s1)]
                     [s2 (f (cdr ls) (+ n m))])
                (do ([i 0 (+ i 1)] [j n (+ j 1)])
                    ((= i m) s2)
                  (string-set! s2 j (string-ref s1 i))))))))

Even in a language that helpfully assigned the result of this function to the first argument under the covers, this is more or less what you fundamentally have to do, as long as strings are represented by arrays (in Haskell, strings are linked lists, so this doesn't apply).

0: http://www.scheme.com/tspl4/objects.html#./objects:h8

[auggierose]

In a functional language lists are immutable, too.