You say: "SPUR also used these tags together with a small number of special LISP instructions to speed up the fundamental LISP list operations like car and cdr (car takes the first item of a list and cdr creates a new list with all except the first item):...". Note that cdr doesn't actually create (allocate) anything; it just returns the contents of the "cdr" ("next") field in the cons cell that is its argument. So at the implementation level, car and cdr are almost identical.
Thanks Paul' LISP isn't my specialist subject as you can probably tell. Better to say 'returns a list with all except the first item' Am I right that the original list remains intact?
You say: "SPUR also used these tags together with a small number of special LISP instructions to speed up the fundamental LISP list operations like car and cdr (car takes the first item of a list and cdr creates a new list with all except the first item):...". Note that cdr doesn't actually create (allocate) anything; it just returns the contents of the "cdr" ("next") field in the cons cell that is its argument. So at the implementation level, car and cdr are almost identical.
Thanks Paul' LISP isn't my specialist subject as you can probably tell. Better to say 'returns a list with all except the first item' Am I right that the original list remains intact?
That is correct.