String processing

[Robert L.]

Pierre Mai wrote:

> > We've had this discussion before. Perl was designed to make file scanning
> > and pattern matching easy. The programs we've been designing in this
> > thread are precisely the kind of application that Perl is intended for.
> > I'm well-enough versed in Lisp to know that the equivalent of:
> >
> > while (<>) { # Loop over input lines
> > counter++ if /^\s*\(/; # if first non-white character is open-paren, count i
> t
> > }
> >
> > would be much more verbose without being significantly more expressive.
> -------------
>
> If it weren't for the regexp, which needs a comment of 10 words to
> explain what it does, and which is easy to get wrong (either comment,
> or regexp that is), I could believe that statement, but so I have to
> humbly disagree ;)
>
> Anyways, this is Common Lisp:
>
> (loop for line = (read-line *standard-input* nil nil)
> while line
> count (starts-with (left-trim-whitespace line) "("))
>
> This uses two trivial string functions which are probably part of
> every working CL user[1]. With an extensible LOOP facility, this could
> even be clarified further...
....
> Footnotes:
> [1] Here are some very simple, inefficient sample implementations:
> (defun starts-with (string substring)
> "Detect whether the `string' starts with `substring'."
> (eql 0 (search substring string)))
>
> (defun left-trim-whitespace (string &optional (ws-bag '(#\Space #\Tab)))
> "Trims any whitespace characters (i.e. characters in `ws-bag') from
> the left side of `string'."
> (string-left-trim ws-bag string))

Gauche Scheme or Racket.

(use srfi-13) ; string functions for Gauche
(use srfi-42) ; sum-ec for Gauche
or
(require srfi/13) ; string functions for Racket
(require srfi/42) ; sum-ec for Racket

(sum-ec (:port line (current-input-port) read-line)
(if (string-prefix? "(" (string-trim line)))
1)