From 42f3325d88c1f3c1f5c70cad4e93a26bb9e81c6c Mon Sep 17 00:00:00 2001
From: AlexKnauth <alexander@knauth.org>
Date: Fri, 28 Aug 2015 00:33:58 -0400
Subject: [PATCH 1/7] add lens-join/assoc

---
 unstable/lens/join-assoc.rkt | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)
 create mode 100644 unstable/lens/join-assoc.rkt

diff --git a/unstable/lens/join-assoc.rkt b/unstable/lens/join-assoc.rkt
new file mode 100644
index 0000000..7ae1cf3
--- /dev/null
+++ b/unstable/lens/join-assoc.rkt
@@ -0,0 +1,32 @@
+#lang sweet-exp racket/base
+
+provide lens-join/assoc
+
+require lens/private/base/main
+        lens/private/compound/join-list
+        lens/private/list/assoc
+        racket/match
+        unstable/sequence
+module+ test
+  require rackunit lens/private/list/main
+
+(define (lens-join/assoc . ks/lenses)
+  (match-define (list (list keys lenses) ...)
+    (for/list ([k/lens (in-slice 2 ks/lenses)])
+      k/lens))
+  (define key-lenses (map assoc-lens keys))
+  (define list-lens (apply lens-join/list lenses))
+  (make-lens
+   (λ (tgt)
+     (for/list ([k (in-list keys)] [lens (in-list lenses)])
+       (cons k (lens-view lens tgt))))
+   (λ (tgt nvw)
+     (lens-set list-lens tgt (apply lens-view/list nvw key-lenses)))))
+
+module+ test
+  (define a-b-lens (lens-join/assoc 'a first-lens
+                                    'b third-lens))
+  (check-equal? (lens-view a-b-lens '(1 2 3))
+                '((a . 1) (b . 3)))
+  (check-equal? (lens-set a-b-lens '(1 2 3) '((a . 100) (b . 200)))
+                '(100 2 200))

From 59a1b7473a0f7a174e898404736af8f24e2d69cf Mon Sep 17 00:00:00 2001
From: AlexKnauth <alexander@knauth.org>
Date: Fri, 28 Aug 2015 09:42:12 -0400
Subject: [PATCH 2/7] add alternating->assoc-list etc.

---
 lens/private/compound/join-hash.rkt    | 22 +++-------
 lens/private/compound/join-list.rkt    | 26 +++++------
 lens/private/util/alternating-list.rkt | 61 ++++++++++++++++++++++++++
 unstable/lens/isomorphism/data.rkt     |  3 ++
 unstable/lens/join-assoc.rkt           |  9 ++--
 5 files changed, 85 insertions(+), 36 deletions(-)
 create mode 100644 lens/private/util/alternating-list.rkt

diff --git a/lens/private/compound/join-hash.rkt b/lens/private/compound/join-hash.rkt
index a393e69..c4d1050 100644
--- a/lens/private/compound/join-hash.rkt
+++ b/lens/private/compound/join-hash.rkt
@@ -5,6 +5,7 @@
          unstable/sequence
          fancy-app
          "../base/main.rkt"
+         "../util/alternating-list.rkt"
          "../util/immutable.rkt"
          "../util/list-pair-contract.rkt"
          "join-list.rkt")
@@ -18,27 +19,14 @@
   [lens-join/hash (->* () #:rest (listof2 any/c lens?) (lens/c any/c immutable-hash?))]))
 
 
-(define (value-list->hash keys vs)
-  (make-immutable-hash (map cons keys vs)))
-
-(define (split-slice n vs)
-  (define grouped
-    (for/list ([group (in-slice n vs)])
-      group))
-  (define (get-ith i)
-    (map (list-ref _ i) grouped))
-  (build-list n get-ith))
-
-(module+ test
-  (check-equal? (split-slice 3 '(a 1 FOO b 2 BAR c 3 BAZ))
-                '((a b c) (1 2 3) (FOO BAR BAZ))))
-
+(define (keys+values->hash keys vs)
+  (make-immutable-hash (keys+values->assoc-list keys vs)))
 
 (define (lens-join/hash . keys/lenses)
-  (match-define (list keys lenses) (split-slice 2 keys/lenses))
+  (define-values [keys lenses] (alternating-list->keys+values keys/lenses))
   (define list-lens (apply lens-join/list lenses))
   (define (get target)
-    (value-list->hash keys (lens-view list-lens target)))
+    (keys+values->hash keys (lens-view list-lens target)))
   (define (set target new-view-hash)
     (lens-set list-lens target (map (hash-ref new-view-hash _) keys)))
   (make-lens get set))
diff --git a/lens/private/compound/join-list.rkt b/lens/private/compound/join-list.rkt
index 08f9ebc..55c970a 100644
--- a/lens/private/compound/join-list.rkt
+++ b/lens/private/compound/join-list.rkt
@@ -1,26 +1,24 @@
-#lang racket/base
+#lang sweet-exp racket/base
 
-(require racket/list
-         racket/contract
-         "../base/main.rkt")
+require racket/list
+        racket/contract
+        "../base/main.rkt"
+        "../util/alternating-list.rkt"
 
-(module+ test
-  (require rackunit
-           "../list/list-ref-take-drop.rkt"))
+module+ test
+  require rackunit
+          "../list/list-ref-take-drop.rkt"
 
-(provide
- (contract-out
-  [lens-join/list (->* () #:rest (listof lens?) (lens/c any/c list?))]))
+provide
+  contract-out
+    lens-join/list (->* () #:rest (listof lens?) (lens/c any/c list?))
 
 
-(define (zip xs ys)
-  (append-map list xs ys))
-
 (define (lens-join/list . lenses)
   (define (get target)
     (apply lens-view/list target lenses))
   (define (set target new-views)
-    (apply lens-set/list target (zip lenses new-views)))
+    (apply lens-set/list target (keys+values->alternating-list lenses new-views)))
   (make-lens get set))
 
 
diff --git a/lens/private/util/alternating-list.rkt b/lens/private/util/alternating-list.rkt
new file mode 100644
index 0000000..b57d5b4
--- /dev/null
+++ b/lens/private/util/alternating-list.rkt
@@ -0,0 +1,61 @@
+#lang sweet-exp racket/base
+
+provide alternating->assoc-list
+        assoc->alternating-list
+        keys+values->assoc-list
+        assoc-list->keys+values
+        keys+values->alternating-list
+        alternating-list->keys+values
+
+require racket/list
+        racket/match
+        unstable/sequence
+module+ test
+  require rackunit
+
+(define (alternating->assoc-list alternating-list)
+  (for/list ([lst (in-slice 2 alternating-list)])
+    (match-define (list a b) lst)
+    (cons a b)))
+
+(define (assoc->alternating-list alist)
+  (append*
+   (for/list ([(k v) (in-pairs alist)])
+     (list k v))))
+
+(define (keys+values->assoc-list keys values)
+  (map cons keys values))
+
+(define (assoc-list->keys+values alist)
+  (values (map car alist)
+          (map cdr alist)))
+
+(define (keys+values->alternating-list keys values)
+  (append-map list keys values))
+
+(define (alternating-list->keys+values alternating-list)
+  (for/lists (ks vv) ([lst (in-slice 2 alternating-list)])
+    (match-define (list k v) lst)
+    (values k v)))
+
+module+ test
+  (check-equal? (alternating->assoc-list '(a 1 b 2)) '((a . 1) (b . 2)))
+  (check-equal? (alternating->assoc-list '(b 2 a 1)) '((b . 2) (a . 1)))
+  (check-equal? (assoc->alternating-list '((a . 1) (b . 2))) '(a 1 b 2))
+  (check-equal? (assoc->alternating-list '((b . 2) (a . 1))) '(b 2 a 1))
+  (check-equal? (keys+values->assoc-list '(a b) '(1 2)) '((a . 1) (b . 2)))
+  (check-equal? (keys+values->assoc-list '(b a) '(2 1)) '((b . 2) (a . 1)))
+  (check-equal? (keys+values->alternating-list '(a b) '(1 2)) '(a 1 b 2))
+  (check-equal? (keys+values->alternating-list '(b a) '(2 1)) '(b 2 a 1))
+  (let-values ([(ks vs) (assoc-list->keys+values '((a . 1) (b . 2)))])
+    (check-equal? ks '(a b))
+    (check-equal? vs '(1 2)))
+  (let-values ([(ks vs) (assoc-list->keys+values '((b . 2) (a . 1)))])
+    (check-equal? ks '(b a))
+    (check-equal? vs '(2 1)))
+  (let-values ([(ks vs) (alternating-list->keys+values '(a 1 b 2))])
+    (check-equal? ks '(a b))
+    (check-equal? vs '(1 2)))
+  (let-values ([(ks vs) (alternating-list->keys+values '(b 2 a 1))])
+    (check-equal? ks '(b a))
+    (check-equal? vs '(2 1)))
diff --git a/unstable/lens/isomorphism/data.rkt b/unstable/lens/isomorphism/data.rkt
index e7ea405..1187443 100644
--- a/unstable/lens/isomorphism/data.rkt
+++ b/unstable/lens/isomorphism/data.rkt
@@ -10,6 +10,7 @@ provide string->symbol-lens
         string->list-lens
 
 require lens/private/base/main
+        lens/private/util/alternating-list
         "base.rkt"
 
 module+ test
@@ -24,6 +25,8 @@ module+ test
   (make-isomorphism-lenses list->vector vector->list))
 (define-values [list->string-lens string->list-lens]
   (make-isomorphism-lenses list->string string->list))
+(define-values [alternating->assoc-list-lens assoc->alternating-list-lens]
+  (make-isomorphism-lenses alternating->assoc-list assoc->alternating-list))
 
 
 (module+ test
diff --git a/unstable/lens/join-assoc.rkt b/unstable/lens/join-assoc.rkt
index 7ae1cf3..c398a53 100644
--- a/unstable/lens/join-assoc.rkt
+++ b/unstable/lens/join-assoc.rkt
@@ -5,21 +5,20 @@ provide lens-join/assoc
 require lens/private/base/main
         lens/private/compound/join-list
         lens/private/list/assoc
+        lens/private/util/alternating-list
         racket/match
         unstable/sequence
 module+ test
   require rackunit lens/private/list/main
 
 (define (lens-join/assoc . ks/lenses)
-  (match-define (list (list keys lenses) ...)
-    (for/list ([k/lens (in-slice 2 ks/lenses)])
-      k/lens))
+  (define-values [keys lenses]
+    (alternating-list->keys+values ks/lenses))
   (define key-lenses (map assoc-lens keys))
   (define list-lens (apply lens-join/list lenses))
   (make-lens
    (λ (tgt)
-     (for/list ([k (in-list keys)] [lens (in-list lenses)])
-       (cons k (lens-view lens tgt))))
+     (keys+values->assoc-list keys (lens-view list-lens tgt)))
    (λ (tgt nvw)
      (lens-set list-lens tgt (apply lens-view/list nvw key-lenses)))))
 

From d13145e6eaced25e6f4e0ad61156eaf3fd2bc1e0 Mon Sep 17 00:00:00 2001
From: AlexKnauth <alexander@knauth.org>
Date: Sun, 30 Aug 2015 17:27:46 -0400
Subject: [PATCH 3/7] provide and document lens-join/assoc

---
 unstable/lens/join-assoc.scrbl | 18 ++++++++++++++++++
 unstable/lens/main.rkt         |  1 +
 unstable/lens/main.scrbl       |  1 +
 3 files changed, 20 insertions(+)
 create mode 100644 unstable/lens/join-assoc.scrbl

diff --git a/unstable/lens/join-assoc.scrbl b/unstable/lens/join-assoc.scrbl
new file mode 100644
index 0000000..3b69d1e
--- /dev/null
+++ b/unstable/lens/join-assoc.scrbl
@@ -0,0 +1,18 @@
+#lang scribble/manual
+
+@(require lens/private/doc-util/main)
+
+@title{Joining lenses with an association list}
+
+@defmodule[unstable/lens/join-assoc]
+
+@defproc[(lens-join/assoc [key key/c] [lens (lens/c target/c value/c)] ... ...)
+         (lens/c target/c (listof (cons/c key/c value/c)))]{
+Like @racket[lens-join/hash], except joins the keys and values into an
+association list instead of a hash-table.
+@lens-unstable-examples[
+  (define a-b-lens (lens-join/assoc 'a first-lens
+                                    'b third-lens))
+  (lens-view a-b-lens '(1 2 3))
+  (lens-set a-b-lens '(1 2 3) '((a . 100) (b . 200)))
+]}
diff --git a/unstable/lens/main.rkt b/unstable/lens/main.rkt
index faa51dd..4393467 100644
--- a/unstable/lens/main.rkt
+++ b/unstable/lens/main.rkt
@@ -3,6 +3,7 @@
 "dict-nested.rkt"
 "if.rkt"
 "isomorphism.rkt"
+"join-assoc.rkt"
 "mapper.rkt"
 "match.rkt"
 "set-filterer.rkt"
diff --git a/unstable/lens/main.scrbl b/unstable/lens/main.scrbl
index dd30ab7..10d51a5 100644
--- a/unstable/lens/main.scrbl
+++ b/unstable/lens/main.scrbl
@@ -16,6 +16,7 @@ this library being backwards-compatible.
   "dict-nested.scrbl"
   "if.scrbl"
   "isomorphism.scrbl"
+  "join-assoc.scrbl"
   "mapper.scrbl"
   "match.scrbl"
   "set-filterer.scrbl"

From 730363fbfd0b681e45ffd6781688d01c2ee307ff Mon Sep 17 00:00:00 2001
From: AlexKnauth <alexander@knauth.org>
Date: Sun, 30 Aug 2015 17:35:57 -0400
Subject: [PATCH 4/7] Use lens/c contracts in docs for other lens-join forms

---
 lens/private/compound/join-hash.scrbl   | 3 ++-
 lens/private/compound/join-list.scrbl   | 2 +-
 lens/private/compound/join-string.scrbl | 2 +-
 lens/private/compound/join-vector.scrbl | 3 ++-
 4 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/lens/private/compound/join-hash.scrbl b/lens/private/compound/join-hash.scrbl
index f11dcf7..5fe63ab 100644
--- a/lens/private/compound/join-hash.scrbl
+++ b/lens/private/compound/join-hash.scrbl
@@ -3,7 +3,8 @@
 @(require "../doc-util/main.rkt")
 
 
-@defproc[(lens-join/hash [key any/c] [lens lens?] ... ...) lens?]{
+@defproc[(lens-join/hash [key key/c] [lens (lens/c target/c value/c)] ... ...)
+         (lens/c target/c (hash/c key/c value/c #:immutable #t))]{
   Constructs a lens that combines the view of each
   @racket[lens] into a hash of views with @racket[key]s
   as the hash keys. In the same manner as @racket[lens-join/list],
diff --git a/lens/private/compound/join-list.scrbl b/lens/private/compound/join-list.scrbl
index e9f9cd1..e835b1c 100644
--- a/lens/private/compound/join-list.scrbl
+++ b/lens/private/compound/join-list.scrbl
@@ -2,7 +2,7 @@
 
 @(require "../doc-util/main.rkt")
 
-@defproc[(lens-join/list [lens lens?] ...) lens?]{
+@defproc[(lens-join/list [lens (lens/c target/c item/c)] ...) (lens/c target/c (listof item/c))]{
   Constructs a lens that combines the view of each
   @racket[lens] into a list of views. This lens can
   be used to view and set a list of values in a single
diff --git a/lens/private/compound/join-string.scrbl b/lens/private/compound/join-string.scrbl
index 8db5482..7d958fe 100644
--- a/lens/private/compound/join-string.scrbl
+++ b/lens/private/compound/join-string.scrbl
@@ -3,7 +3,7 @@
 @(require "../doc-util/main.rkt")
 
 
-@defproc[(lens-join/string [lens lens?] ...) lens?]{
+@defproc[(lens-join/string [lens (lens/c target/c char?)] ...) (lens/c target/c immutable-string?)]{
   Like @racket[lens-join/list], except the view is a string, not a list.
   Each @racket[lens] argument must return a @racket[char?] as a view.
   @lens-examples[
diff --git a/lens/private/compound/join-vector.scrbl b/lens/private/compound/join-vector.scrbl
index d8ea98f..66bda68 100644
--- a/lens/private/compound/join-vector.scrbl
+++ b/lens/private/compound/join-vector.scrbl
@@ -3,7 +3,8 @@
 @(require "../doc-util/main.rkt")
 
 
-@defproc[(lens-join/vector [lens lens?] ...) lens?]{
+@defproc[(lens-join/vector [lens (lens/c target/c item/c)] ...)
+         (lens/c target/c (vector-immutableof item/c))]{
   Like @racket[lens-join/list], except the view is a vector, not a list.
   @lens-examples[
     (define vector-first-third-fifth-lens

From 1bcf4fb74e5bfe5c4be6ff171f4c4bb41c8e87db Mon Sep 17 00:00:00 2001
From: AlexKnauth <alexander@knauth.org>
Date: Sun, 30 Aug 2015 19:42:12 -0400
Subject: [PATCH 5/7] use rest-> contract for lens-join/list

---
 lens/private/compound/join-list.rkt | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lens/private/compound/join-list.rkt b/lens/private/compound/join-list.rkt
index 55c970a..14a0ba7 100644
--- a/lens/private/compound/join-list.rkt
+++ b/lens/private/compound/join-list.rkt
@@ -4,6 +4,7 @@ require racket/list
         racket/contract
         "../base/main.rkt"
         "../util/alternating-list.rkt"
+        "../util/rest-contract.rkt"
 
 module+ test
   require rackunit
@@ -11,7 +12,7 @@ module+ test
 
 provide
   contract-out
-    lens-join/list (->* () #:rest (listof lens?) (lens/c any/c list?))
+    lens-join/list (rest-> lens? (lens/c any/c list?))
 
 
 (define (lens-join/list . lenses)

From c6c15305b21459889be7cd9811343c2afb4d9170 Mon Sep 17 00:00:00 2001
From: AlexKnauth <alexander@knauth.org>
Date: Sun, 30 Aug 2015 19:45:33 -0400
Subject: [PATCH 6/7] add contract for lens-join/assoc

---
 unstable/lens/join-assoc.rkt | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/unstable/lens/join-assoc.rkt b/unstable/lens/join-assoc.rkt
index c398a53..32e76ae 100644
--- a/unstable/lens/join-assoc.rkt
+++ b/unstable/lens/join-assoc.rkt
@@ -1,11 +1,15 @@
 #lang sweet-exp racket/base
 
-provide lens-join/assoc
+require racket/contract/base
+provide
+  contract-out
+    lens-join/assoc (->* [] #:rest (listof2 any/c lens?) (lens/c any/c (listof pair?)))
 
 require lens/private/base/main
         lens/private/compound/join-list
         lens/private/list/assoc
         lens/private/util/alternating-list
+        lens/private/util/list-pair-contract
         racket/match
         unstable/sequence
 module+ test

From 3babd97c4c018eb888ed25e832ea8b06f6c83091 Mon Sep 17 00:00:00 2001
From: AlexKnauth <alexander@knauth.org>
Date: Sun, 30 Aug 2015 19:47:45 -0400
Subject: [PATCH 7/7] Revert "Use lens/c contracts in docs for other lens-join
 forms"

This reverts commit 730363fbfd0b681e45ffd6781688d01c2ee307ff.
---
 lens/private/compound/join-hash.scrbl   | 3 +--
 lens/private/compound/join-list.scrbl   | 2 +-
 lens/private/compound/join-string.scrbl | 2 +-
 lens/private/compound/join-vector.scrbl | 3 +--
 4 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/lens/private/compound/join-hash.scrbl b/lens/private/compound/join-hash.scrbl
index 5fe63ab..f11dcf7 100644
--- a/lens/private/compound/join-hash.scrbl
+++ b/lens/private/compound/join-hash.scrbl
@@ -3,8 +3,7 @@
 @(require "../doc-util/main.rkt")
 
 
-@defproc[(lens-join/hash [key key/c] [lens (lens/c target/c value/c)] ... ...)
-         (lens/c target/c (hash/c key/c value/c #:immutable #t))]{
+@defproc[(lens-join/hash [key any/c] [lens lens?] ... ...) lens?]{
   Constructs a lens that combines the view of each
   @racket[lens] into a hash of views with @racket[key]s
   as the hash keys. In the same manner as @racket[lens-join/list],
diff --git a/lens/private/compound/join-list.scrbl b/lens/private/compound/join-list.scrbl
index e835b1c..e9f9cd1 100644
--- a/lens/private/compound/join-list.scrbl
+++ b/lens/private/compound/join-list.scrbl
@@ -2,7 +2,7 @@
 
 @(require "../doc-util/main.rkt")
 
-@defproc[(lens-join/list [lens (lens/c target/c item/c)] ...) (lens/c target/c (listof item/c))]{
+@defproc[(lens-join/list [lens lens?] ...) lens?]{
   Constructs a lens that combines the view of each
   @racket[lens] into a list of views. This lens can
   be used to view and set a list of values in a single
diff --git a/lens/private/compound/join-string.scrbl b/lens/private/compound/join-string.scrbl
index 7d958fe..8db5482 100644
--- a/lens/private/compound/join-string.scrbl
+++ b/lens/private/compound/join-string.scrbl
@@ -3,7 +3,7 @@
 @(require "../doc-util/main.rkt")
 
 
-@defproc[(lens-join/string [lens (lens/c target/c char?)] ...) (lens/c target/c immutable-string?)]{
+@defproc[(lens-join/string [lens lens?] ...) lens?]{
   Like @racket[lens-join/list], except the view is a string, not a list.
   Each @racket[lens] argument must return a @racket[char?] as a view.
   @lens-examples[
diff --git a/lens/private/compound/join-vector.scrbl b/lens/private/compound/join-vector.scrbl
index 66bda68..d8ea98f 100644
--- a/lens/private/compound/join-vector.scrbl
+++ b/lens/private/compound/join-vector.scrbl
@@ -3,8 +3,7 @@
 @(require "../doc-util/main.rkt")
 
 
-@defproc[(lens-join/vector [lens (lens/c target/c item/c)] ...)
-         (lens/c target/c (vector-immutableof item/c))]{
+@defproc[(lens-join/vector [lens lens?] ...) lens?]{
   Like @racket[lens-join/list], except the view is a vector, not a list.
   @lens-examples[
     (define vector-first-third-fifth-lens