CODEWITHSUNDEEP
lispcommon-lispclisp
userX
userX

Reputation: 23

How to write two values on one line in LISP?

I'm new to LISP and just started self learning. I want to print the value of p side by side using write-line. What I want to see is p=x:

(setq p 10987)

(write-line "p=")
(write p)

the result looks like this:

p=
10987

I want to achieve p=10987 in the same line.

Upvotes: 0

Views: 673

Answers (2)

ad absurdum
ad absurdum

Reputation: 21359

There is no need to use write-line with format; just use format alone.

Note that setq and setf are intended for mutation of existing variables; they are not intended to establish new bindings, and the Common Lisp specification does not define any behavior for the posted code. Typically implementations do what you would expect, but don't attempt to define new variables using setq or setf in code that matters. Some implementations, e.g., SBCL, issue warnings in such cases.

Common ways to establish new bindings include defvar, defparameter, or let:

CL-USER> (defparameter *p* 10987)
*P*
CL-USER> (format t "*p*=~A~%" *p*)
*p*=10987
NIL

Here defparameter establishes a binding to *p*; setf or setq could be used to update this binding now. Note that *p* has earmuffs, which are conventionally used in Common Lisp to indicate dynamically scoped variables.

The first argument to format specifies the output destination. If it is t, then the output is to *standard-output*; if nil then format returns a string result. You can also specify a particular stream, or an existing string with a fill pointer as destinations. The ~A in the call to format is the aesthetic directive, which usually does what you want when your goal is to print a value for a person to read. The ~% directive causes format to emit a newline; with this there is no need for write-line to be used at all.

Another (more awkward) approach would be to use princ and terpri:

CL-USER> (let ((p 10987))
           (princ "p=")
           (princ p)
           (terpri))
p=10987
NIL

Here p is a locally scoped variable, hence no earmuffs. princ is used to print an object in human-readable form, but it does not emit a newline. The arcanely-named terpri emits a newline.

Upvotes: 3

Martin Půda
Martin Půda

Reputation: 7576

(setq p 10987)
(write-line (format nil "p=~a" p))

Upvotes: 0

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