Merge pull request #132 from calmm-js/feature/drop-removal-of-empty-t…

…hings-by-default

Drop dy default removal of empty arrays, objects, and strings

CHANGELOG.md

@@ -1,12 +1,28 @@
-# Changelog
+# Partial Lenses Changelog
 
-## 12.0.0
+## 13.0.0
+
+As discussed in issue
+[#131](https://github.com/calmm-js/partial.lenses/issues/131), optics working on
+arrays, objects, and strings, no longer remove empty values by default.  It
+appears that by default removal, on average, makes optics compositions more
+complex.  In most cases this change means that uses of `L.define` or
+`L.required` with an empty value `{}`, `[]`, or `""`, can simply be removed.
+`L.define` and `L.required` now give a warning in case they are used with an
+empty value and a matching empty value passes through them redundantly.  In
+cases where removal of empty values is desired, one can e.g. compose with
+`L.defaults`.
+
+Removed previously obsoleted `L.findHint`.
 
 The current plan is to change Partial Lenses to support so called naked or
 prototypeless objects with `null` prototype (i.e. `Object.create(null)`) in the
 next major version.  This is a breaking change although it is likely that it
 will not affect most users.  Usefully warning for this change of behaviour by
-adding diagnostics to optics seems somewhat difficult.
+adding diagnostics to optics seems somewhat difficult.  *This note was moved
+from 12.0.0.*
+
+## 12.0.0
 
 As documented in 11.21.0:
 * Support for lazy algebras with the `delay` function was removed.
@@ -114,7 +130,7 @@ bug fix as the behaviour wasn't previously strictly specified.
 ## 10.0.0
 
 As discussed in issue
-[50](https://github.com/calmm-js/partial.lenses/issues/50), to strongly guide
+[#50](https://github.com/calmm-js/partial.lenses/issues/50), to strongly guide
 away from mutating data structures, optics now
 [`Object.freeze`](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/freeze)
 any new objects they create when `NODE_ENV` is not `production`.  Note that

EXERCISES.md

@@ -86,8 +86,6 @@ test('rem', L.remove(lens,           nested), undefined)
     search for an object with the given key.</span>
 * Support removal.
   * <span class="hint">Use [`L.removable`](/#L-valueOr).</span>
-* Make it so that the array does not become `undefined` once empty.
-  * <span class="hint">Use [`L.define`](/#L-define).</span>
 * Support insertion and make it so that keys remain ordered.
   * <span class="hint">Use [`L.valueOr`](/#L-valueOr) to add the `key`
     property in case there is no matching object.</span>
@@ -148,10 +146,8 @@ test('set_ext', L.set(end, 4, {start: 1, num: 2, xtra: 'field'}), {start: 1, num
 * Define a traversal that targets the `x` properties of the coordinate pairs.
   * <span class="hint">Compose [`L.elems`](/#L-elems) and
     [`'x'`](/#L-prop).</span>
-* Support removal so that the whole coordinate pair is removed and removing the
-  last one produces an empty array.
+* Support removal so that the whole coordinate pair is removed.
   * <span class="hint">Use [`L.removable`](/#L-removable).</span>
-  * <span class="hint">Use [`L.define`](/#L-define).</span>
 
 ```js
 const xs = '???'