Merge pull request #350 from knorth55/last-optional-n

add &optional n in last

Author: k-okada

doc/jlatex/jsequences.tex

@@ -236,8 +236,8 @@ \subsection{リスト}
 \funcdesc{nthcdr}{count list}{
 {\em list}に{\bf cdr}を{\em count}回適用した後のリストを返す。}
 
-\funcdesc{last}{list}{
-{\em list}の最後の要素でなく、最後のconsを返す。}
+\funcdesc{last}{list \&optional (n 1)}{
+{\em list}の最後の要素でなく、最後の{\em n}個のconsを返す。}
 
 \funcdesc{butlast}{list \&optional (n 1)}
 {{\em list}の最後から{\em n}個の要素を削除したリストを返す。}

doc/latex/sequences.tex

@@ -237,8 +237,8 @@ \subsection{Lists}
 \funcdesc{nthcdr}{count list}{
 applies {\bf cdr} {\em count} times to {\em list}.}
 
-\funcdesc{last}{list}{
-the last cons is returned, not the last element.}
+\funcdesc{last}{list \&optional (n 1)}{
+the last {\em n} conses is returned, not the last element.}
 
 \funcdesc{butlast}{list \&optional (n 1)}
 { returns a list which does not contain the last {\em n} elements.}

lisp/l/common.l

@@ -448,9 +448,10 @@ if pos is bigger than the length of list, item is nconc'ed at the tail"
      (nconc result1 result2)))
 
 (defun rotate-list (l) (append (cdr l) (list (car l))))
-(defun last (x)
-  (while (consp (cdr x)) (setq x (cdr x)))
-  x)
+(defun last (x &optional (n 1))
+  (unless (and (integerp n) (>= n 0))
+    (error "last &optional n must be a non negative integer"))
+  (nthcdr (max (- (length x) n) 0) x))
 (defun copy-tree (x) (subst t t x))
 (defun copy-list (x) (nreverse (reverse x)))
 (defun nreconc (x y) (nconc (nreverse x) y))