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nil IS a list...

tweeks 
ddGetObjChildren( 
b_objId 
) 
=> l_children | nil

When you say l_children, isn't it already implied that the list could be empty?  After all, if the object has no children, then you get nil, which is just a zero-length list of children.  So shouldn't the return type be simply l_children, like this:

ddGetObjChildren( 
b_objId 
) 
=> l_children

Just sayin'....

Parents
  • tweeks

    skillUser said:
    Well, yes, but it is clear enough to say that the return value is nil otherwise some folks might expect (nil) to indicate no children, so it doesn't hurt to be redundant in this case I think...


    That's a good point. 

    Curiously, I haven't encountered many SKILL functions that return a (nil) so as to distinguish the result from nil.  In fact, the only one that comes to mind is errset, so that you can distinguish a function that returns nil successfully from one that throws an error.

    It just so happens that today I thought about writing a macro exists1 that is just like exists except it takes the car of whatever exists returns, since I'm usually searching for the first thing matching the predicate, not the rest of the list starting with the first thing matching the predicate....  However, if I were searching for nil, I wouldn't know whether (exists1 x myList (p x)) => nil means nil is present in myList, or nil is not present!  (This is one disadvantage to not having a separate boolean type like Scheme.  Of course, even then I'd have the same issue if I were searching for a Scheme boolean false #f object... which is one disadvantage to not having a Maybe type like Haskell....)

    I could have exists1 return a wrapped result, so that I'd get (nil) if nil was in there, and nil if it wasn't, but that's what exists does... :)

    For me, it seems more convenient to live with the ambiguity and just return nil in either case, since I never search for nil using exists anyway -- I would use something like (apply (and ...)) or andmap for that.

Reply
  • tweeks

    skillUser said:
    Well, yes, but it is clear enough to say that the return value is nil otherwise some folks might expect (nil) to indicate no children, so it doesn't hurt to be redundant in this case I think...


    That's a good point. 

    Curiously, I haven't encountered many SKILL functions that return a (nil) so as to distinguish the result from nil.  In fact, the only one that comes to mind is errset, so that you can distinguish a function that returns nil successfully from one that throws an error.

    It just so happens that today I thought about writing a macro exists1 that is just like exists except it takes the car of whatever exists returns, since I'm usually searching for the first thing matching the predicate, not the rest of the list starting with the first thing matching the predicate....  However, if I were searching for nil, I wouldn't know whether (exists1 x myList (p x)) => nil means nil is present in myList, or nil is not present!  (This is one disadvantage to not having a separate boolean type like Scheme.  Of course, even then I'd have the same issue if I were searching for a Scheme boolean false #f object... which is one disadvantage to not having a Maybe type like Haskell....)

    I could have exists1 return a wrapped result, so that I'd get (nil) if nil was in there, and nil if it wasn't, but that's what exists does... :)

    For me, it seems more convenient to live with the ambiguity and just return nil in either case, since I never search for nil using exists anyway -- I would use something like (apply (and ...)) or andmap for that.

Children
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