Merge pull request #149 from AlexKnauth/reverse-last

add reverse-lens and last-lens

unstable/lens/list.rkt

@@ -0,0 +1,31 @@
+#lang racket/base
+
+(require racket/contract/base)
+(provide (contract-out
+          [reverse-lens
+           (lens/c list? list?)]
+          [last-lens
+           (lens/c list? any/c)]
+          ))
+
+(require lens/base/main
+         lens/list/main
+         lens/compound/main
+         "isomorphism/base.rkt"
+         )
+
+(module+ test
+  (require rackunit fancy-app))
+
+(define reverse-lens
+  (isomorphism-lens reverse reverse))
+
+(define last-lens
+  (lens-thrush reverse-lens first-lens))
+
+(module+ test
+  (check-equal? (lens-view reverse-lens '(1 2 3)) '(3 2 1))
+  (check-equal? (lens-transform reverse-lens '(1 2 3) (cons 4 _)) '(1 2 3 4))
+  (check-equal? (lens-view last-lens '(1 2 3)) 3)
+  (check-equal? (lens-set last-lens '(1 2 3) 'a) '(1 2 a))
+  )