provide and document lens-join/assoc

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)))
+]}

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"

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"