suzanne.soy/racket
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

part of the previous commit (rev10555)

Browse Source 
svn: r10556
This commit is contained in:
Eli Barzilay 2008-07-02 10:05:19 +00:00
parent 1002366103
commit f820f00e66
1 changed files with 6 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
collects/srfi/1/selector.ss
View File

@ -35,7 +35,7 @@
#lang scheme/base
(require srfi/optional
(only-in scheme/list take drop))
(only-in scheme/list take drop take-right drop-right))
(provide first second
third fourth
@ -90,6 +90,7 @@
;; off by K, then chasing down the list until the lead pointer falls off
;; the end.
#; ; provided by scheme/list
(define (take-right lis k)
(check-arg integer? k 'take-right)
(let lp ((lag lis) (lead (drop lis k)))
@ -97,6 +98,7 @@
(lp (cdr lag) (cdr lead))
lag)))
#; ; provided by scheme/list
(define (drop-right lis k)
(check-arg integer? k 'drop-right)
(let recur ((lag lis) (lead (drop lis k)))
@ -134,6 +136,9 @@
(set-cdr! prev '())
(values x suffix))))
;; these could be reprovided from scheme/base, but they don't raise an
;; error on improper lists
(define (last lis) (car (last-pair lis)))
(define (last-pair lis)