6.5 Lists

6.5.1 car, cdr, cons, append, reverse, length

car(list)

:: The first element of the given non-null list list.

cdr(list)

:: A list obtained by removing the first element of the given non-null list list.

cons(obj,list)

:: A list obtained by adding an element obj to the top of the given list list.

append(list1,list2)

:: A list obtained by adding all elements in the list list2 according to the order as it is to the last element in the list list1.

reverse(list)

:: reversed list of list.

length(list|vect)

:: Number of elements in a list list and a vector vect.

return

car() : arbitrary, cdr(), cons(), append(), reverse() : list, length() : non-negative integer

list list1 list2

list

obj

arbitrary

• A list is written in Asir as [obj1,obj2,…]. Here, obj1 is the first element.
• Function car() outputs the first element of a non-null list. For a null list, the result should be undefined. In the current implementation, however, it outputs a null list. This treatment for a null list may subject to change in future, and users are suggested not to use the tentative treatment for a null list for serious programming.
• Function cdr() outputs a list obtained by removing the first element from the input non-null list. For a null list, the result should be undefined. In the current implementation, however, it outputs a null list. This treatment for a null list may subject to change in future, and users are suggested not to use the tentative treatment for a null list for serious programming.
• Function cons() composes a new list from the input list list and an arbitrary object obj by adding obj to the top of list.
• Function append() composes a new list, which has all elements of list1 in the same ordering followed by all elements of list2 in the same ordering.
• Function reverse() returns a reversed list of list.
• Function length() returns a non-negative integer which is the number of elements in the input list list and the input vector vect. Note that function size should be used for counting elements of matrix.
• Lists are read-only objects in Asir. There elements cannot be modified.
• The n-th element in a list can be referred to by applying the function cdr() n times repeatedly and cdr() at last. A more convenient way to access to the n-th element is the use of bracket notation, that is, to attach an index [n] like vectors and matrices. The system, however, follow the n pointers to access the desired element. Subsequently, much time is spent for an element located far from the top of the list.
• Function cdr() does not create a new cell (a memory quantity). Function append(), as a matter of fact, repeats cons() for as many as the length of list1 the first argument. Subsequently, append() consumes much memory space if its first argument is long. Similar argument applies to function reverse().

[0] L = [[1,2,3],4,[5,6]];
[[1,2,3],4,[5,6]]
[1] car(L);
[1,2,3]
[2] cdr(L);
[4,[5,6]]
[3] cons(x*y,L);
[y*x,[1,2,3],4,[5,6]]
[4] append([a,b,c],[d]);
[a,b,c,d]
[5] reverse([a,b,c,d]);
[d,c,b,a]
[6] length(L);
3
[7] length(ltov(L));
3
[8] L[2][0];
5

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