From f763204514af7fdeefbe48bd34b39ed361a27bd7 Mon Sep 17 00:00:00 2001
From: AlexKnauth <alexander@knauth.org>
Date: Tue, 7 Jul 2015 22:54:41 -0400
Subject: [PATCH] add dict-ref-lens

---
 lens/dict.rkt   | 16 ++++++++++++++++
 lens/dict.scrbl | 22 ++++++++++++++++++++++
 lens/main.scrbl |  1 +
 3 files changed, 39 insertions(+)
 create mode 100644 lens/dict.rkt
 create mode 100644 lens/dict.scrbl

diff --git a/lens/dict.rkt b/lens/dict.rkt
new file mode 100644
index 0000000..6d4e04c
--- /dev/null
+++ b/lens/dict.rkt
@@ -0,0 +1,16 @@
+#lang racket/base
+
+(provide dict-ref-lens)
+
+(require racket/dict fancy-app "base/main.rkt")
+(module+ test
+  (require rackunit))
+
+(define (dict-ref-lens key)
+  (make-lens (dict-ref _ key)
+             (dict-set _ key _)))
+
+(module+ test
+  (check-equal? (lens-transform* '((a . 1) (b . 2) (c . 3)) (dict-ref-lens 'a) (* 100 _))
+                '((a . 100) (b . 2) (c . 3)))
+  )
diff --git a/lens/dict.scrbl b/lens/dict.scrbl
new file mode 100644
index 0000000..b39a28c
--- /dev/null
+++ b/lens/dict.scrbl
@@ -0,0 +1,22 @@
+#lang scribble/manual
+
+@(require scribble/eval
+          "lenses-examples.rkt"
+          (for-label lens
+                     lens/dict
+                     racket/base
+                     racket/contract))
+
+
+@title{Dict lenses}
+
+@defmodule[lens/dict]
+
+@defproc[(dict-ref-lens [key any/c]) lens?]{
+  Returns a lens for viewing the value mapped to @racket[key] in a dict.
+  @lenses-examples[
+    (require lens/dict)
+    (define dict '((a . 1) (b . 2) (c . 3)))
+    (lens-view (dict-ref-lens 'a) dict)
+    (lens-set (dict-ref-lens 'a) dict 100)
+]}
diff --git a/lens/main.scrbl b/lens/main.scrbl
index c3662a1..d417977 100644
--- a/lens/main.scrbl
+++ b/lens/main.scrbl
@@ -16,4 +16,5 @@ source code: @url["https://github.com/jackfirth/lens"]
 @include-section["base/main.scrbl"]
 @include-section["list/main.scrbl"]
 @include-section["struct.scrbl"]
+@include-section["dict.scrbl"]
 @include-section["applicable.scrbl"]