Topic: GetX With Default

[Lee Mac]

This code is from a little while ago, written as a generic function to get user input with a 'remembered' default.

I would like to share it here and open the floor to suggestions for improvement or perhaps alternatives that you guys use for the same purpose 

Code: [Select]

(defun LM:GetXWithDefault ( _function _prompt _symbol _default / _toString )
  ;; © Lee Mac 2010
 
  (setq _toString
    (lambda ( x )
      (cond
        ( (eq getangle _function) (angtos x) )
        ( (eq 'REAL (type x))       (rtos x) )
        ( (eq 'INT  (type x))       (itoa x) )
        ( x )
      )
    )
  )
 
  (set _symbol
    (
      (lambda ( input ) (if (or (not input) (eq "" input)) (eval _symbol) input))
      (_function (strcat _prompt "<" (_toString (set _symbol (cond ( (eval _symbol) ) ( _default )))) "> : "))
    )
  )
)

Example:

Code: [Select]

(defun c:test nil
  (LM:GetXWithDefault getreal "\nEnter Number " '*num* 1.0)
)

[JohnK]

Practical application: Not the greatest idea (I thought about it myself). Off the top of my head; You will have a problem with name spaces i would imagine.

Academically, I agree with the principle.

[Lee Mac]

Thanks for your input Se7en - I considered it for use when multiple prompts are issued in a program, each perhaps using different functions/prompts.

When you speak about problems with namespaces, would this take effect if the application were to be compiled with a separate namespace, or were you talking in general?

[JohnK]

Compiled. but i never researched it. You will have to do that yourself.

As always, I am always cautious but this is how i would/did it (this is in my notes on the subject, however i never applied or used it).

Code: [Select]

(defun aif ( var expr iffalse )
    ;; anaphoric-if
    ;;
    ;; ported to AutoLisp from ?comonLisp?
    ;; I dont know the whole extents of the CL`aif' function, im only
    ;; working from one small definition.
    ;;
    ;; EX:
    ;;     (aif 'a (getint "\nEnter new value [1]: ") 1)
    ;;
    ;; OR (if you want to recall `a'...)
    ;; (aif 'a
    ;;      (getint
    ;;        (strcat
    ;;         "\nEnter new value [" (if a (rtos a 2 0) (rtos 1 2 0)) "]: "))
    ;;      (if a a 1) )
    ;;
    (set var (cond (expr) (iffalse))) )

[JohnK]

Sorry I am am still a bit busy but I wanted to tell you to check the way your procedure evaluates. -i.e. Try to initiate a call and cancel it in the mid of the prompt. ...You may end up with a nasty (hard to track down) bug.

Command: (LM:GetXWithDefault getreal "\nEnter Number " '*num* 1.0)

Enter Number <1.0000> : *Cancel*
; error: Function cancelled

Command: !*num*
1.0

Command: (aif 'a (getint "\nEnter new value [1]: ") 1)

Enter new value [1]: *Cancel*
; error: Function cancelled

Command: !a
nil

[Kerry]

It's really interesting to see your evolution Lee.
Reminds be of the phases I went through 15 or 20 years ago ; and similar growth by several others here and elsewhere over the years.

and those phases ARE a good thing, 'cause they provide a solid conceptual base to work from.

You'll probably change your mind about do-all getx functions in favour of purpose specific bomb-proof methods for each type.

case in point : adding initget and keyword options to each oh the get options.

I recall a couple of conversations between CAB and myself that were particularly productive in that regard.

[CAB]

Ah yes, good times they were. I learned a lot from those conversations. 

http://www.theswamp.org/index.php?topic=6992.0

[alanjt]

A limit would be any additional arguments (basepoint for getdist, T to allow strings with spaces for getstring, etc.).
Granted, this could easily be avoided by appending a list with the message and eval'ing it.

eg.

Code: [Select]

(eval (append (list getstring T) (list (strcat _prompt "blah blah"))))

[JohnK]

@alanjt
I'm not sure i follow what you mean. Are you referring to this structure of function call?
As in: "(LM:GetXWithDefault getreal "\nEnter Number " '*num* 1.0)"

If so, i highly recommend using my method (where the "procedure call" is its own entity in itself).
(aif 'a (getint "\nEnter new value [1]: ") 1)

[alanjt]

I'm not disagreeing with you.
I was just pointing out a hole in Lee's routine.

eg.

Code: [Select]

(LM:GetXWithDefault getstring "\nSpecify string " '*string* "something")With the above, one could only type wordswithoutspaces. Any option for hidden arguments is removed.

[JohnK]

Yes, okay. I understood you then.

[alanjt]

Yes, okay. I understood you then.

I like your method, very interesting approach.

[JohnK]

Yes, okay. I understood you then.

I like your method, very interesting approach.

*lol* you would be the first (Thank you).

If you like that, then you may like this (?related?).

Code: [Select]

(defun let ( bindings body / replace )
  ;; let
  ;; evaluate process with localized variables.
  ;;
  ;; Ported to AutoLisp By: John (7)
  ;;
  ;; Explination of Let:
  ;; [ http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-12.html#%_sec_1.3.2 ]
  ;;
  ;;
  ;; Synopsis: let <bindings> <body>
  ;;
  ;;  (let '((a (+ 1 (* x y)))
  ;;         (b (- 1 y)))
  ;;     '(+ (* x (square a))
  ;;         (* y b)
  ;;         (* a b)))
  ;;  ~~>
  ;;  ((LAMBDA nil (+ (* X (SQUARE (+ 1 (* X Y))))
  ;;  (* Y (- 1 Y))
  ;;  (* (+ 1 (* X Y)) (- 1 Y)))))
  ;;
  ;;  ==> Evaluated value
  ;;
  ;; EX1:
  ;;  (setq x 5)
  ;;  (+ (let '((x 3))
  ;;          '(+ x (* x 10)))
  ;;   x)
  ;; 
  ;;  ==> 38
  ;; 
  ;; EX2:
  ;;  (setq x 2 y 4)
  ;;  (let '((x 3)
  ;;         (y (+ x 2)))
  ;;       '(* x y))
  ;; 
  ;;  ==> 12
  ;;
  ;; EX3:
  ;;
  ;;  ( (lambda ( / let )
  ;;    (defun let (bindings body)
  ;;      (eval
  ;;        (cons (append (list 'lambda (mapcar 'car bindings)) body)
  ;;              (mapcar 'cadr bindings))) )
  ;;
  ;;    (let
  ;;      '((ss-vp
  ;;          (ssget "x"
  ;;                 (list '(0 . "VIEWPORT")
  ;;                       '(-4 . "/=")
  ;;                       '(68 . 1)
  ;;                       (cons 410 (getvar "ctab"))))))
  ;;      '((if (null ss-vp)
  ;;          (progn
  ;;            (alert "\n No VIEWPORTS in current layout")
  ;;            (princ) )
  ;;          ss-vp))
  ;;      )
  ;;    )
  ;; )
  ;;
  ;; ==>
    (eval
        (cons (append (list 'lambda (mapcar 'car bindings)) body)
              (mapcar 'cadr bindings))) )

[JohnK]

I should mention that these are purely academic and not really practical.

[Lee Mac]

Sorry I am am still a bit busy but I wanted to tell you to check the way your procedure evaluates. -i.e. Try to initiate a call and cancel it in the mid of the prompt. ...You may end up with a nasty (hard to track down) bug.

Command: (LM:GetXWithDefault getreal "\nEnter Number " '*num* 1.0)

Enter Number <1.0000> : *Cancel*
; error: Function cancelled

Command: !*num*
1.0

Command: (aif 'a (getint "\nEnter new value [1]: ") 1)

Enter new value [1]: *Cancel*
; error: Function cancelled

Command: !a
nil

True, the default symbol is set to the first-time default upon evaluation, but, I don't believe this is an issue as the default symbol will have some value whatever the user presses, (other than Esc). But thanks for pointing it out.