read words from a file into nested list in common lisp programming language - lisp

Question

I have a file named test.txt, it contains
"hello this is a test file"
I want to read it from the file so that every word represents lists of character and every paragraph represents lists of words means that I want to store them into a nested list like:
(list(list (h e l l o)) (list(t h i s))(list(i s)) (list(a)) (list(t e s t)) (list(f i l e))))
I am totally new in lisp and have a lot of confusion about this problem.

Answer 1

Solution without any dependencies
(defun split (l &key (separators '(#\Space #\Tab #\Newline)) (acc '()) (tmp '()))
(cond ((null l) (nreverse (if tmp (cons (nreverse tmp) acc) acc)))
((member (car l) separators)
(split (cdr l) :separators separators
:acc (if tmp (cons (nreverse tmp) acc) acc)
:tmp '()))
(t
(split (cdr l) :separators separators
:acc acc
:tmp (cons (car l) tmp)))))
(defun read-file-lines (file-path)
(with-open-file (f file-path :direction :input)
(loop for line = (read-line f nil)
while line
collect line)))
(defun read-file-to-word-characters (file-path)
(mapcan (lambda (s) (split (coerce s 'list)))
(read-file-lines file-path)))
(read-file-to-word-characters "~/test.lisp.txt")
;; ((#\h #\e #\l #\l #\o) (#\t #\h #\i #\s) (#\i #\s) (#\a) (#\t #\e #\s #\t)
;; (#\f #\i #\l #\e))
Convert the characters to one-letter strings:
;; apply to elements of nested list (= a tree) the conversion function `string`
(defun map-tree (fn tree)
(cond ((null tree) '())
((atom tree) (funcall fn tree))
(t (mapcar (lambda (branch) (map-tree fn branch)) tree))))
(map-tree #'string (read-file-to-word-characters "~/test.lisp.txt"))
;; (("h" "e" "l" "l" "o") ("t" "h" "i" "s") ("i" "s") ("a") ("t" "e" "s" "t")
;; ("f" "i" "l" "e"))
Content of "~/test.lisp.txt":
hello this
is a test file
Solution using cl-ppcre (Edi Weitz's congenial regex package)
;; look here in an answer how to use cl-ppcre:split
;; https://stackoverflow.com/questions/15393797/lisp-splitting-input-into-separate-strings
(ql:quickload :cl-ppcre)
(defun read-file-lines (file-path)
(with-open-file (f file-path :direction :input)
(loop for line = (read-line f nil)
while line
collect line)))
(defun string-to-words (s) (cl-ppcre:split "\\s+" s))
(defun to-single-characters (s) (coerce s 'list))
(defun read-file-to-character-lists (file-path)
(mapcan (lambda (s)
(mapcar #'to-single-characters
(string-to-words s)))
(read-file-lines file-path)))
(read-file-to-character-lists "~/test.lisp.txt")
;; ((#\h #\e #\l #\l #\o) (#\t #\h #\i #\s) (#\i #\s) (#\a) (#\t #\e #\s #\t)
;; (#\f #\i #\l #\e))
;; or use above's function:
(map-tree #'string (read-file-to-character-lists "~/test.lisp.txt"))
;; (("h" "e" "l" "l" "o") ("t" "h" "i" "s") ("i" "s") ("a") ("t" "e" "s" "t")
;; ("f" "i" "l" "e"))
;; or:
(defun to-single-letter-strings (s) (cl-ppcre:split "\\s*" s))
(defun read-file-to-letter-lists (file-path)
(mapcan (lambda (s)
(mapcar #'to-single-letter-strings
(string-to-words s)))
(read-file-lines file-path)))
(read-file-to-letter-lists "~/test.lisp.txt")
;; (("h" "e" "l" "l" "o") ("t" "h" "i" "s") ("i" "s") ("a") ("t" "e" "s" "t")
;; ("f" "i" "l" "e"))