Added last-pair and tests

svn: r9422

original commit: 13c5e3812d252bab985f29210862308ae8623396

collects/mzlib/list.ss

@@ -1,10 +1,9 @@
+#lang mzscheme
 
-(module list mzscheme
+;; The `first', etc. operations in this library
+;;  work on pairs, not lists.
 
-  ;; The `first', etc. operations in this library
-  ;;  work on pairs, not lists.
-
-  (require (only scheme/base
+(require (only scheme/base
                foldl
                foldr
 
@@ -25,9 +24,10 @@
          (only scheme/list
                cons?
                empty?
-                 empty))
+               empty
+               last-pair))
 
-  (provide first
+(provide first
          second
          third
          fourth
@@ -65,8 +65,8 @@
          sort
          merge-sorted-lists)
 
-  ;; a non-destructive version for symmetry with merge-sorted-lists!
-  (define (merge-sorted-lists a b less?)
+;; a non-destructive version for symmetry with merge-sorted-lists!
+(define (merge-sorted-lists a b less?)
   (cond [(null? a) b]
         [(null? b) a]
         [else (let loop ([x (car a)] [a (cdr a)] [y (car b)] [b (cdr b)])
@@ -81,14 +81,14 @@
                     (list* x y b)
                     (cons x (loop (car a) (cdr a) y b)))))]))
 
-  ;; deprecated!
-  (define quicksort sort)
-  (define mergesort sort)
+;; deprecated!
+(define quicksort sort)
+(define mergesort sort)
 
-  (define (first x)
+(define (first x)
   (unless (pair? x) (raise-type-error 'first "non-empty list" x))
   (car x))
-  (define-syntax define-lgetter
+(define-syntax define-lgetter
   (syntax-rules ()
     [(_ name npos)
      (define (name l0)
@@ -97,24 +97,15 @@
            (if (eq? pos 1) (car l) (loop (cdr l) (sub1 pos)))
            (raise-type-error
             'name (format "list with ~a or more items" npos) l0))))]))
-  (define-lgetter second  2)
-  (define-lgetter third   3)
-  (define-lgetter fourth  4)
-  (define-lgetter fifth   5)
-  (define-lgetter sixth   6)
-  (define-lgetter seventh 7)
-  (define-lgetter eighth  8)
+(define-lgetter second  2)
+(define-lgetter third   3)
+(define-lgetter fourth  4)
+(define-lgetter fifth   5)
+(define-lgetter sixth   6)
+(define-lgetter seventh 7)
+(define-lgetter eighth  8)
 
-  (define (rest x)
+(define (rest x)
   (unless (pair? x)
     (raise-type-error 'rest "non-empty list" x))
   (cdr x))
-
-  (define (last-pair l)
-    (if (pair? l)
-      (let loop ([l l] [x (cdr l)])
-        (if (pair? x)
-          (loop x (cdr x))
-          l))
-      (raise-type-error 'last-pair "pair" l))))
-