topic Re: "and", no not the function. Help with evaluating 2 expressions in Visual LISP, AutoLISP and General Customization Forum

"and", no not the function. Help with evaluating 2 expressions

Anonymous — Thu, 01 Sep 2016 16:36:37 GMT

Hi all.

Need to call on your expertise again.

I find many times where I want to say "and" in my routines, For example in "plain" English:

"If Angle1 is less than 0 and Angle2 is greater than 0, then SETQ....blah blah blah

Is there a function or expression that lets you do this?

Ultimately find a work around with multiple if statements or cond. It always seems to get messy and convoluted.

Is there a simpler way to evaluate/compare to arguments like that?

Any help is appreciated.

Thank you

Re: "and", no not the function. Help with evaluating 2 expressions

Shneuph — Thu, 01 Sep 2016 16:53:49 GMT

You're saying you're looking for an alternative to the AND function?

(If (and

(< Angle1 0)

(> Angle2 0)

);and

(setq .....)

);if

Re: "and", no not the function. Help with evaluating 2 expressions

ВeekeeCZ — Thu, 01 Sep 2016 17:01:34 GMT

And actually IS the function.

Your example.

(if (and (< angle1 0)
	 (> angle2 0)
	 )
  (setq blah "blah"))

It could even be used in following syntax. The result is the same.

(and (< angle1 0)
     (> angle2 0)
     (setq blah "blah")
     )

Re: "and", no not the function. Help with evaluating 2 expressions

Anonymous — Thu, 01 Sep 2016 16:59:59 GMT

Thank You! Your examples were quite helpful

I was confused by the cryptic definition of AND I was looking at.

"...Arguments
expr Any expression.
Return Values
Nil, if any of the expressions evaluate to nil; otherwise T. If and is issued
without arguments, it returns T.
Examples
Command: (setq a 103 b nil c "string")
"string"
Command: (and 1.4 a c)
T
Command: (and 1.4 a b c)
nil"

your examples make perfect sense.

Thanks Again.

Re: "and", no not the function. Help with evaluating 2 expressions

ВeekeeCZ — Thu, 01 Sep 2016 17:09:26 GMT

@Anonymous wrote:

Thank You! Your examples were quite helpful

I was confused by the cryptic definition of AND I was looking at.

"...Arguments
expr Any expression.
Return Values
Nil, if any of the expressions evaluate to nil; otherwise T. If and is issued
without arguments, it returns T.
Examples
Command: (setq a 103 b nil c "string")
"string"
Command: (and 1.4 a c)
T
Command: (and 1.4 a b c)
nil"

your examples make perfect sense.

Thanks Again.

The number 1.4 inside of and does not make much sence. It's always T. But testing variables (and a b c) for not nil, that makes the sence.

BTW an empty string variable (setq a "") is True.

Re: "and", no not the function. Help with evaluating 2 expressions

steve_carson — Thu, 01 Sep 2016 17:24:18 GMT

Thanks for the info regarding an empty string, BeekeeCZ.

I think it's weird that an empty string is T, but an empty list is nil...

Command: (and "")
T

Command: (and '())
nil

Command: (= '() nil)
T

Steve

Re: "and", no not the function. Help with evaluating 2 expressions

Kent1Cooper — Thu, 01 Sep 2016 17:38:15 GMT

@steve_carson wrote:

....

I think it's weird that an empty string is T, but an empty list is nil...

....

Just to add another to that list of empty things that may or may not be nil:

The result of (ssget), if nothing is selected or found, is nil, not an empty selection set. But empty selection sets can "exist" -- if you remove everything from a selection set with (ssdel) functions, or start an empty one via (ssadd) with no items-do-add argument, it may be empty and have an (sslength) of 0, but it still "exists" and is not nil.

Re: "and", no not the function. Help with evaluating 2 expressions

john.uhden — Thu, 01 Sep 2016 22:43:37 GMT

Kudos to you!
Do you remember Stephan Koster too?
He's the one that got me hooked on anding.
Technically, it stops further evaluations if any returns nil.

Re: "and", no not the function. Help with evaluating 2 expressions

ВeekeeCZ — Fri, 02 Sep 2016 07:59:24 GMT

@john.uhden wrote:
Kudos to you!
Do you remember Stephan Koster too?
He's the one that got me hooked on anding.
Technically, it stops further evaluations if any returns nil.

Thanks! Unfortunately I have no idea how this guy is, although I know you've noticed him before. But I remember were I saw this 'odd' usage of and function for the first time - it made me a little thinking about it. It was @Kent1Cooper 's ReportAngle routine HERE.

Another interesting constructions using similar principle are...

(or dst
    (initget 5)
    (setq dst (getdist "\nSet distance: "))
    )

;;;;;

(setq dst (cond ((getdist "\nSet distance <10>: "))
		(10)))

Re: "and", no not the function. Help with evaluating 2 expressions

martti.halminen — Fri, 02 Sep 2016 08:28:15 GMT

The rules about truth values in the Lisp language family (except Scheme) can be expressed quite simply:

1. The symbol NIL and the empty list are the same object, there is no way to distinguish between them.

2. NIL is the only thing that is considered false in a boolean context (IF, COND, AND, OR etc.)

3. Anything else whatsoever is considered as true.

Re: "and", no not the function. Help with evaluating 2 expressions

martti.halminen — Fri, 02 Sep 2016 08:39:11 GMT

I'd write the last one slightly differently:

(setq dst (cond ((getdist "\nSet distance <10>: "))
		(T 10)))

but that is just a style preference.

This is a little contrived construction, usually only seen in AutoLISP.

That would be legal also in other Lisps, but there this can be done in a simpler way, because in other Lisps OR returns the value of the last thing it evaluated, instead of T:

(setq dst (or (getdist "\nSet distance <10>: ")
              10))