PRINT function does not display anything prior to a READ function call

[A.S. Dhillon]

Possible Issue: PRINT function does not display anything prior to a READ function call and variable assignment

Environment: 64-bit SBCL 1.3.15 running under 64-bit Windows 10 (version 1607) on my Dell XPS laptop (Intel Core i7-2720QM CPU, 8GB Ram).

I pass the following source file to SBCL using either --script or --load at the command line, and the PRINT function does not display anything prior to a read function call and variable assignment.

However, if I type something and press enter, then the PRINT function displays the missing text string on the same line as the hello-you function output.

--------------------------------------------------------
;;; Source file: lisp-tutorial_v1.cl

(print "What's your name?") ;; Does not work under SBCL! Works under Clozure CL.

(defvar *name* (read))

(defun hello-you (*name*)
  (format t "Hello ~a! ~%" *name*))

(setq *print-case* :capitalize)

(hello-you *name*)

(quit)
---------------------------------------------------------

Example1: There's a blank line where I would expect the text "What's your name?" printed before entering John.

C:\src\00.lisp>sbcl --script "lisp-tutorial_v1.cl"

John
"What's your name?" Hello John!

C:\src\00.lisp>

---------------------------------------------------------

Example2: The same issue occurs when using --load rather than --script.

C:\src\00.lisp>sbcl --noinform --load "lisp-tutorial_v1.cl"

Jane
"What's your name?" Hello Jane!

C:\src\00.lisp>

-----------------------------------------------------------

Example3: The PRINT function works under Clozure CL without any issue.

C:\src\00.lisp>wx86cl64 -l "lisp-tutorial_v1.cl"

"What's your name?" John
Hello John!

C:\src\00.lisp>

-------------------------------------------------------------

[Stas Boukarev (stassats)]

Use FINISH-OUTPUT.

[A.S. Dhillon (ninejaguar)]

Thank you for clarifying. I had not realized that SBCL on Windows always requires an extra step to flush the buffered output stream with the FINISH-OUTPUT function or FORCE-OUTPUT function when printing to the command line/shell. Whereas, Clozure CL and CLISP work as commonly expected when printing to a command line/shell, and do not require an extra step to flush the buffer.

This works as a workaround in SBCL on Windows per your suggestion, and it works with Clozure CL as well although it is not required:

;;; Source file: lisp-tutorial_v1.cl
(setq *print-case* :capitalize)

;; Print does not work in SBCL without flushing the buffered output stream.
;; Print does work in Clozure CL and CLISP without explicitly flushing the output stream buffer.
(print "What's your name?")

(FINISH-OUTPUT) ;; explicitly flushes the buffered output stream, even if empty.

(defvar *name* (read))

(defun hello-you (newName)
  (format t "Hello ~a! ~%" newName))

(hello-you *name*)

(quit)

-------------------------------------------

Example1: Using FINISH-OUTPUT after PRINT flushes the SBCL's buffered output stream.

C:\src\00.lisp>sbcl --script lisp-tutorial_v1.cl

"What's your name?" John
Hello John!

C:\src\00.lisp>

--------------------------------------------

Example2: Using FINISH-OUTPUT after PRINT to flush an empty output stream buffer does not cause an error in Clozure CL, although it is redundant.

C:\src\00.lisp>wx86cl64 -l lisp-tutorial_v1.cl

"What's your name?" Jane
Hello Jane!

C:\src\00.lisp>

[Attila Lendvai (attila-lendvai)]

it's not a workaround, you cannot expect unbuffered output, not even if sometimes, somewhere, it works without finish-output.