Why does SBCL print Sublis like this?

Question

So the function:

(defun royal-we ()
  (sublis '((i  .  we))
      '(if I learn lisp I will be pleased)))

The output in SBCL is printed this way:

(IF WE
    LEARN
    LISP
    WE
    WILL
    BE
    PLEASED)

Yet the example one:

(sublis '((roses . violets)  (red . blue))
        '(roses are red))

gives the output

(VIOLETS ARE BLUE)

Why is SBCL printing the atoms of the list on different lines, unlikeo other distributions like Clisp?

There are no newlines in the resulting list, it's just how SBCL prints it. CCL and CLISP for example print the list on a single line. — uselpa
O, thanks :) I appreciate the quick answer. Do you know why it prints that way? — Floofk
Sorry no I don't use SBCL I had a quick look at the documentation and I didn't find any parameter that would lead to this. Somebody more knowledgeable in SBCL might be able to explain this. — uselpa
It might have something to do with Common Lisp indendation for certain symbols when found in code, such as for the special operator if. — acelent

BRPocock BRPocock · Accepted Answer · 2015-12-02T19:46:09

The (if …) list is being handled by the pretty-printer under the assumption that it's (potentially) an actual Lisp form.

CL-USER> (setf *print-pretty* nil)
NIL
CL-USER> '(if 1 2 3)
(IF 1 2 3)
CL-USER> (setf *print-pretty* t)
T
CL-USER> '(if 1 2 3)
(IF 1
    2
    3)

You'll find that, among other things, let forms will also be indented similarly, and certain loop symbols will start new lines. There are a few other effects.

CL-USER> '(loop for thing in stuff with boo = 4 count mice)
(LOOP FOR THING IN STUFF
      WITH BOO = 4
      COUNT MICE)
CL-USER> '(let 1 2 3)
(LET 1
  2
  3)
CL-USER> '(defun 1 nil 2 3)
(DEFUN 1 () 2 3)
CL-USER> (setf *print-pretty* nil)
NIL
CL-USER> '(defun 1 nil 2 3)
(DEFUN 1 NIL 2 3)

BTW, the relevant standards are found … http://www.lispworks.com/documentation/lw60/CLHS/Body/22_b.htm … if you were to, say, want to reprogram it for your purposes.

For just printing data lists, I'd suspect disabling pretty-printing or using FORMAT would probably suffice, though.

eg,

 (format t "~&~@(~{~a~^ ~}~)" '(violets are blue))
 Violets are blue

Why does SBCL print Sublis like this?

1 Answers