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File input/output: Difference between revisions
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In this task, the job is to create a file called "output.txt", and place in it the contents of the file "input.txt", ''via an intermediate variable.'' In other words, your program will demonstrate: (1) how to read from a file into a variable, and (2) how to write a variable's contents into a file. Oneliners that skip the intermediate variable are of secondary interest — operating systems have copy commands for that.
=={{header|ACL2}}==
<lang lisp>:set-state-ok t
(defun read-channel (channel limit state)
(mv-let (ch state)
(read-char$ channel state)
(if (or (null ch)
(zp limit))
(let ((state (close-input-channel channel state)))
(mv nil state))
(mv-let (so-far state)
(read-channel channel (1- limit) state)
(mv (cons ch so-far) state)))))
(defun read-from-file (filename limit state)
(mv-let (channel state)
(open-input-channel filename :character state)
(mv-let (contents state)
(read-channel channel limit state)
(mv (coerce contents 'string) state))))
(defun write-channel (channel cs state)
(if (endp cs)
(close-output-channel channel state)
(let ((state (write-byte$ (char-code (first cs))
channel state)))
(let ((state (write-channel channel
(rest cs)
state)))
state))))
(defun write-to-file (filename str state)
(mv-let (channel state)
(open-output-channel filename :byte state)
(write-channel channel (coerce str 'list) state)))
(defun copy-file (in out state)
(mv-let (contents state)
(read-from-file in (expt 2 40) state)
(write-to-file out contents state)))</lang>
=={{header|Ada}}==
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