provide and document hash-filterer-lens etc.

unstable/lens/hash-filterer.scrbl

@@ -0,0 +1,35 @@
+#lang scribble/manual
+
+@(require lens/private/doc-util/main)
+
+@title{Filtering hash-tables}
+
+@defmodule[unstable/lens/hash-filterer]
+
+@defproc[(hash-filterer-lens/key [keep? (-> any/c boolean?)])
+         (lens/c immutable-hash? immutable?)]{
+Creates a lens that filters a hash-table to keys that pass the predicate
+@racket[keep?].
+@lens-unstable-examples[
+  (lens-view (hash-filterer-lens/key symbol?) (hash 'a 1 "b" 2 'c 3))
+  (lens-set (hash-filterer-lens/key symbol?) (hash 'a 1 "b" 2 'c 3) (hash 'd 4 'e 5))
+]}
+
+@defproc[(hash-filterer-lens/value [keep? (-> any/c boolean?)])
+         (lens/c immutable-hash? immutable?)]{
+Like @racket[hash-filterer-lens/value], but filters based on values that pass
+@racket[keep?], not keys.
+@lens-unstable-examples[
+  (lens-view (hash-filterer-lens/value number?) (hash 'a 1 'b "two" 'c 3))
+  (lens-set (hash-filterer-lens/value number?) (hash 'a 1 'b "two" 'c 3) (hash 'd 4))
+]}
+
+@defproc[(hash-filterer-lens [keep? (-> any/c any/c boolean?)])
+         (lens/c immutable-hash? immutable?)]{
+Creates a lens that filters a hash-table by the predicate @racket[keep?], which
+takes the key and the value as its two arguments.
+@lens-unstable-examples[
+  (lens-view (hash-filterer-lens =) (hash 1 1.0 2 45 3 3))
+  (lens-set (hash-filterer-lens =) (hash 1 1.0 2 45 3 3) (hash 4 4.0 5.0 5))
+]}
+

unstable/lens/main.rkt

@@ -1,6 +1,7 @@
 #lang reprovide
 "arrow.rkt"
 "dict-nested.rkt"
+"hash-filterer.rkt"
 "if.rkt"
 "isomorphism.rkt"
 "join-assoc.rkt"

unstable/lens/main.scrbl

@@ -14,6 +14,7 @@ this library being backwards-compatible.
 @(include-sections
   "arrow.scrbl"
   "dict-nested.scrbl"
+  "hash-filterer.scrbl"
   "if.scrbl"
   "isomorphism.scrbl"
   "join-assoc.scrbl"