Let's say I have the following list: (A B . D) How I would reproduce this only by using list function ? (list 'A 'B '. 'D) is not working

CodePudding user response：

You cannot. The constructor to create lists are cons. Proper lists are just the empty list or a chain of one or more cons where the last one has the empty list as the cdr. list only creates proper lists. Eg. (list 'a 'b 'c) is a function that does (cons 'a (cons 'b (cons c '()))).

(a b . d) is created with (cons 'a (cons 'b 'd)). It is not a proper list since it is terminated by d and not nil. Thus it is impossible to create this structure with list.

CodePudding user response：

I'm not sure what you are really trying to do here, but this seems to be exactly what

It is then easy to see that there is no value of b which will result in the cdr of the last cons in such a chain being other than nil (aka ()). Therefore lst, and hence list, cannot construct a chain of conses in which cdr of the last cons is other than nil, which means it cannot construct a dotted list, since that is the definition of a dotted list.

CodePudding user response：

We can almost do this with list, but not quite. The point is that list insists on putting a nil at the end of the list, yet we want to have a non-nil value at the end.

We can therefore have a dotted term anywhere but at the end of the list.

I can offer you:

(list 'a '(b . c) 'd) ; has a normal list end of 'd -> 'nil
(list 'a '(b . c))    ; looks like b . c is at the end, but actually 'a is