From: nick_keighley_nospam@...
Date: 2009-02-25T20:24:18+09:00
Subject: Re: reading file to list

On 24 Feb, 15:00, nick_keighley_nos...@hotmail.com wrote:
> On 17 Jan, 17:16, Xah Lee <xah...@gmail.com> wrote:

> > Here's a interesting toy problem posted by Drew Krause to
> > comp.lang.lisp:
>
> > ------------------------
> > On Jan 16, 2:29 pm, Drew Krause wrote [paraphrased a bit]:
>
> > OK, I want to create a nested list in Lisp (always of only integers)
> > from a text file, such that each line in the text file would be
> > represented as a sublist in the 'imported' list.
>
> > example of a file's content
>
> > 3 10 2
> > 4 1
> > 11 18
>
> > example of programing behavior
> > (make-list-from-text "blob.txt") => ((3 10 2) (4 1) (11 18))

<snip>

> scheme:
>
> (define (read-line port)
>     (define (rec-read-line port line)
>         (define next-char (peek-char port))
>         (define number #f)
>         (cond ((eof-object? next-char) '())
>               ((char=? next-char #\newline) (read-char port) line)
>               ((char-numeric? next-char)
>                    (set! number (read port))
>                    (cons number (rec-read-line port line)))
>               ((char=? next-char #\space)
>                    (read-char port)
>                    (rec-read-line port line))
>               (else (error (string-append "bad character \""
>                               (string next-char) "\"")))
>     ))
>
>     (rec-read-line port '())
> )
>
> (define (make-int-list port)
>     (define line (read-line port))
>     (if (null? line)
>         '()
>         (cons line (make-int-list port))))
>
> (define (make-list-from-text file)
>     (make-int-list (open-input-file file)))

an assignment-free version

(define (read-line port)
    (define (rec-read-line port line)
        (let ((next-char (peek-char port)))
            (cond ((eof-object? next-char) '())
                  ((char=? next-char #\newline) (read-char port) line)
                  ((char-numeric? next-char)
                       (let ((number (read port)))
                           (cons number (rec-read-line port line))))
                  ((char=? next-char #\space)
                       (read-char port)
                       (rec-read-line port line))
                  (else (error (string-append "bad character \""
                                   (string next-char) "\""))))))

    (rec-read-line port '()))

(define (make-int-list port)
    (let ((line (read-line port)))
        (if (null? line)
            '()
            (cons line (make-int-list port)))))

(define (make-list-from-text file)
    (make-int-list (open-input-file file)))

(define (mk) (make-list-from-text "blob.txt"))

<snip>

number was originally define'd but I discovered there were
limits to where you could define things