From c2c88410245f5173f6ad681e16d6d61f733e6f37 Mon Sep 17 00:00:00 2001
From: AlexKnauth <alexander@knauth.org>
Date: Thu, 27 Aug 2015 21:20:31 -0400
Subject: [PATCH] add dict-ref-nested-lens

---
 unstable/lens/dict-nested.rkt | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)
 create mode 100644 unstable/lens/dict-nested.rkt

diff --git a/unstable/lens/dict-nested.rkt b/unstable/lens/dict-nested.rkt
new file mode 100644
index 0000000..c54b362
--- /dev/null
+++ b/unstable/lens/dict-nested.rkt
@@ -0,0 +1,24 @@
+#lang sweet-exp racket/base
+
+require racket/contract/base
+provide
+  contract-out
+    dict-ref-nested-lens (->* [] #:rest (listof any/c) (lens/c functional-dict? any/c))
+
+require lens/private/base/main
+        lens/private/compound/thrush
+        lens/private/dict
+        lens/private/util/functional-dict
+module+ test
+  require rackunit fancy-app
+
+(define (dict-ref-nested-lens . ks)
+  (apply lens-thrush (map dict-ref-lens ks)))
+
+module+ test
+  (define a-x (dict-ref-nested-lens 'a 'x))
+  (let-lens [val ctxt] a-x '([a . ([x . 1] [y . 2])] '[b . ([z . 3])])
+    (check-equal? val 1)
+    (check-equal? (ctxt 100) '([a . ([x . 100] [y . 2])] '[b . ([z . 3])])))
+  (check-equal? (lens-transform/list '([a . ([x . 1] [y . 2])] '[b . ([z . 3])]) a-x (* 10 _))
+                '([a . ([x . 10] [y . 2])] '[b . ([z . 3])]))