minor code improvements, added ninth and tenth

svn: r8364

collects/scheme/list.ss

@@ -1,61 +1,53 @@
+#lang scheme/base
 
-(module list scheme/base
+(provide first second third fourth fifth sixth seventh eighth ninth tenth
+         last
 
-  (provide first
-           second
-           third
-           fourth
-           fifth
-           sixth
-           seventh
-           eighth
-           last
+         rest
 
-           rest
+         cons?
+         empty
+         empty?)
 
-           cons?
-           empty
-           empty?)
+(define (first x)
+  (if (and (pair? x) (list? x))
+    (car x)
+    (raise-type-error 'first "non-empty list" x)))
 
-  (define (first x)
-    (unless (and (pair? x) 
-                 (list? x))
-      (raise-type-error 'first "non-empty list" x))
-    (car x))
+(define-syntax define-lgetter
+  (syntax-rules ()
+    [(_ name npos)
+     (define (name l0)
+       (if (list? l0)
+         (let loop ([l l0] [pos npos])
+           (if (pair? l)
+             (if (eq? pos 1) (car l) (loop (cdr l) (sub1 pos)))
+             (raise-type-error
+              'name (format "list with ~a or more items" npos) l0)))
+         (raise-type-error 'name "list" 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 ninth   9)
+(define-lgetter tenth   10)
 
-  (define-syntax define-lgetter
-    (syntax-rules ()
-      [(_ name npos)
-       (define (name l0)
-         (if (list? l0)
-             (let loop ([l l0] [pos npos])
-               (if (pair? l)
-                   (if (eq? pos 1) (car l) (loop (cdr l) (sub1 pos)))
-                   (raise-type-error 'name (format "list with ~a or more items" npos) l0)))
-             (raise-type-error 'name "list" 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 (last l)
+  (if (and (pair? l) (list? l))
+    (let loop ([l l])
+      (if (pair? (cdr l))
+        (loop (cdr l))
+        (car l)))
+    (raise-type-error 'last "non-empty list" l)))
 
-  (define (last x)
-    (unless (and (pair? x)
-                 (list? x))
-      (raise-type-error 'last "non-empty list" x))
-    (let loop ([x x])
-      (if (pair? (cdr x))
-          (loop (cdr x))
-          (car x))))
+(define (rest l)
+  (if (and (pair? l) (list? l))
+    (cdr l)
+    (raise-type-error 'rest "non-empty list" l)))
 
-  (define (rest x)
-    (unless (and (pair? x)
-                 (list? x))
-      (raise-type-error 'rest "non-empty list" x))
-    (cdr x))
-
-  (define cons? (lambda (x) (pair? x)))
-  (define empty? (lambda (x) (null? x)))
-  (define empty '()))
+(define cons? (lambda (l) (pair? l)))
+(define empty? (lambda (l) (null? l)))
+(define empty '())

collects/scribblings/reference/pairs.scrbl

@@ -461,6 +461,10 @@ Like @scheme[assoc], but finds an element using the predicate
 
 @defproc[(eighth [lst list?]) any]{Returns the eighth element of the list.}
 
+@defproc[(ninth [lst list?]) any]{Returns the ninth element of the list.}
+
+@defproc[(tenth [lst list?]) any]{Returns the tenth element of the list.}
+
 @defproc[(last [lst list?]) any]{Returns the last element of the list.}
 
 @; ----------------------------------------