@comment $OpenXM: OpenXM/src/asir-doc/parts/builtin/list.texi,v 1.4 2003/12/18 10:26:20 ohara Exp $
\BJP
@node リストの演算,,, 組み込み函数
@section リストの演算
\E
\BEG
@node Lists,,, Built-in Function
@section Lists
\E

@menu
* car cdr cons append reverse length::
@end menu

\JP @node car cdr cons append reverse length,,, リストの演算
\EG @node car cdr cons append reverse length,,, Lists
@subsection @code{car}, @code{cdr}, @code{cons}, @code{append}, @code{reverse}, @code{length}
@findex car
@findex cdr
@findex cons
@findex append
@findex reverse
@findex length

@table @t
@item car(@var{list})
\JP :: 空でない @var{list} の先頭要素. 
\EG :: The first element of the given non-null list @var{list}.
@item cdr(@var{list})
\JP :: 空でない @var{list} から先頭要素を取り除いたリスト. 
\EG :: A list obtained by removing the first element of the given non-null list @var{list}.
@item cons(@var{obj},@var{list})
\JP :: @var{list} の先頭に @var{obj} を付け加えたリスト. 
\EG :: A list obtained by adding an element @var{obj} to the top of the given list @var{list}.
@item @t{append}(@var{list1},@var{list2})
\JP :: @var{list1} と @var{list2} をこの順に 1 つにしたリスト. 
\EG :: A list obtained by adding all elements in the list @var{list2} according to the order as it is to the last element in the list @var{list1}.
@item @t{reverse}(@var{list})
\JP :: @var{list} を逆順にしたリスト. 
\EG :: reversed list of @var{list}.
@item length(@var{list}|@var{vect})
\JP :: @var{list} の長さ, または @var{vect} の長さ. 
\EG :: Number of elements in a list @var{list} and a vector @var{vect}.
@end table

@table @var
@item return
\JP @code{car()} : 任意, @code{cdr()}, @code{cons()}, @code{append()}, @code{reverse()} : リスト,  @code{length()} : 自然数
\EG @code{car()} : arbitrary, @code{cdr()}, @code{cons()}, @code{append()}, @code{reverse()} : list,  @code{length()} : non-negative integer
@item list list1 list2
\JP リスト
\EG list
@item obj
\JP 任意
\EG arbitrary
@end table

@itemize @bullet
\BJP
@item
リストは @t{[}@var{obj1},@var{obj2},...@t{]} と表される. @var{obj1} が
先頭要素である. 
@item
@code{car()} は, 空でない @var{list} の先頭要素を出力する. 空リストが入力された場合は, 空リストが出力される. 
@item 
@code{cdr()} は, 空でない @var{list} から先頭要素を取り除いたリストを出力する. 空リストが入力された場合は, 空リストが出力される. 
@item 
@code{cons()} は,  @var{list} の先頭に @var{obj} を付け加えたリストを出力する. 
@item
@code{append()} は, @var{list1} の要素と @var{list2} のすべての要素を結合させたリスト [@var{list1} の要素の並び,@var{list2} の要素の並び] を出力する. 
@item
@code{reverse()} は, @var{list} を逆順にしたリストを出力する. 
@item
@code{length()} は, @var{list} または @var{vect} の長さを出力する. 行列の要素の個数は, @code{size()} を用いる. 
@item
リストは読み出し専用で, 要素の入れ替えはできない. 
@item
リストの @var{n} 番目の要素の取り出しは, @code{cdr()} を @var{n} 回適用
した後 @code{car()} を適用することにより可能であるが, 便法として, 
ベクトル, 行列などの配列と同様, インデックス @code{[@var{n}]} を後ろに
付けることにより取り出すことができる. ただし, システム内部では, 
実際にポインタを @var{n} 回たどるので, 後ろの要素ほど取り出しに時間がかかる. 
@item
@code{cdr()} は新しいセルを生成しないが, @code{append()} は, 実際には
第 1 引数のリストの長さだけの @code{cons()} の繰り返しとなるため, 
第 1 引数のリストが長い場合には多くのメモリを消費することになる. 
@code{reverse()} に関しても同様である. 
\E
\BEG
@item
A list is written in @b{Asir} as @t{[}@var{obj1},@var{obj2},@dots{}@t{]}.
Here, @var{obj1} is the first element.
@item
Function @code{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.
@item
Function @code{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.
@item
Function @code{cons()} composes a new list from the input list @var{list}
and an arbitrary object @var{obj} by adding @var{obj} to the top of
@var{list}.
@item
Function @code{append()} composes a new list, which has all elements of
@var{list1} in the same ordering followed by all elements of @var{list2}
in the same ordering.
@item
Function @code{reverse()} returns a reversed list of @var{list}.
@item
Function @code{length()} returns a non-negative integer which is the
number of elements in the input list @var{list} and the input vector @var{vect}.
Note that function @code{size} should be used for counting elements
of @var{matrix}.
@item
Lists are read-only objects in @b{Asir}.  There elements cannot be
modified.
@item
The @var{n}-th element in a list can be referred to by applying the
function @code{cdr()} @var{n} times repeatedly and @code{cdr()} at last.
A more convenient way to access to the @var{n}-th element is the use
of bracket notation, that is, to attach an index @code{[@var{n}]}
like vectors and matrices.  The system, however, follow the
@var{n} pointers to access the desired element. Subsequently, much
time is spent for an element located far from the top of the list.
@item
Function @code{cdr()} does not create a new cell (a memory quantity).
Function @code{append()}, as a matter of fact, repeats @code{cons()}
for as many as the length of @var{list1} the first argument.
Subsequently, @code{append()} consumes much memory space if its
first argument is long.
Similar argument applies to function @code{reverse()}.
\E
@end itemize

@example
[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
@end example