[erlang-questions] Strings as Lists

Matthias Lang matthias@REDACTED
Fri Feb 15 21:54:00 CET 2008

David Mercer writes:
 > Out of curiosity, besides as an academic exercise and a point of debate,
 > what is the practical use of reversing a string?  I've been programming for
 > a quarter century and am having trouble remembering when I last needed to
 > reverse a string.  Search? yes; compare? yes; substitute? yes; modify? yes.
 > Just can't think of when I've needed to reverse a string.  Is there some
 > common protocol that requires you to send Unicode strings in reverse order
 > or something?

Many tail-recursive algorithms produce reversed lists, so you need
lists:reverse/1 to put them back again at the end. Typical example:

  to_upper(List) ->
    Rev = to_upper(List, []),

  to_upper([H|T], Acc) ->
    to_upper(T, [H band bnot 16#20|Acc]);
  to_upper([], Acc) ->

Yes, there are other ways of writing to_upper/1.
Yes, I could have put a guard on it.
Yes, I can hear the non-ASCII people grinding their teeth over the band bnot
No, the lists:reverse/1 does not change the big O 


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