write-string, write-line

write-string, write-line Function

Syntax:

write-string string &optional output-stream &key start end → string

write-line string &optional output-stream &key start end → string

Arguments and Values:

string—a string.

output-stream – an output stream designator . The default is standard output.

start, end—bounding index designators of string. The defaults for start and end are 0 and nil, respectively.

Description:

write-string writes the characters of the subsequence of string bounded by start and end to output-stream. write-line does the same thing, but then outputs a newline afterwards.

Examples:

(prog1 (write-string "books" nil :end 4) (write-string "worms")) 
▷ bookworms 
→ "books" 
(progn (write-char #\\*) 
       (write-line "test12" \*standard-output\* :end 5) 
       (write-line "\*test2") 
       (write-char #\\*) 
       nil) 
▷ \*test1 

▷ \*test2 
▷ \* 
→ NIL 

Affected By:

*standard-output*, *terminal-io*.

See Also:

read-line, write-char

Notes:

write-line and write-string return string, not the substring bounded by start and end.

(write-string string)

≡ (dotimes (i (length string)

(write-char (char string i)))

(write-line string)

≡ (prog1 (write-string string) (terpri))

Expanded Reference: write-string, write-line

Basic write-string

write-string writes characters from a string to an output stream. It returns the original string (not the substring).

(with-output-to-string (s)
  (write-string "hello world" s))
=> "hello world"

write-string with :start and :end

The :start and :end keyword arguments select a substring to write.

(with-output-to-string (s)
  (write-string "bookworms" s :end 4))
=> "book"

Basic write-line

write-line works like write-string but appends a newline after the string.

(with-output-to-string (s)
  (write-line "first" s)
  (write-line "second" s))
=> "first
second
"

Combining write-string and write-line

(with-output-to-string (s)
  (write-string "Name: " s)
  (write-line "Alice" s)
  (write-string "Age: " s)
  (write-string "30" s))
=> "Name: Alice
Age: 30"

Return Value

Both functions return the full original string, not the written substring.

(with-output-to-string (s)
  (let ((result (write-string "bookworms" s :end 4)))
    (write-char #\Space s)
    (write-string result s)))
=> "book bookworms"