How to read input until EOF in Lisp

lisp common-lisp eof
Fredrick Pennachi picture Fredrick Pennachi · Aug 21, 2009 · Viewed 8.9k times · Source

How do I read an input stream until EOF in Lisp? In C, you might do it like this:

while ((c = getchar()) != EOF)
{
  // Loop body...
}

I would like to be able to pipe data to my Lisp programs without having to specify the data size in advance. Here's an example from something I'm doing now:

(dotimes (i *n*)
  (setf *t* (parse-integer (read-line) :junk-allowed T))
  (if (= (mod *t* *k*) 0) (incf *count*)))

In this loop, the variable *n* specifies the number of lines I'm piping to the program (the value is read from the first line of input), but I would like to just process an arbitrary and unknown number of lines, stopping when it reaches the end of the stream.

Answer

Rainer Joswig picture Rainer Joswig · Aug 21, 2009

See the HyperSpec for READ-LINE

(loop for line = (read-line stream nil :eof) ; stream, no error, :eof value
      until (eq line :eof)
      do ... )

or sometimes with nil

(loop for line = (read-line stream nil nil)
      while line
      do ... )

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