Operators

Operators

Combinator(s)	w/ Result	Stateful	w/ Result	Notes
Control.Lens (Getting)
view / ^.		use		View single target, or fold multiple monoidal targets. view (to snd) ("hello","world") == "world" -- convert prelude.snd function into lens view _2 ("hello","world") == "world" -- same thing view _2 ("hello","world","yeeha") == "world" -- but also works on triples! ("hello","world") ^. _2 == "world" [Sum 3, Sum 4] ^. each == Sum 7 use works just like view except in a MonadState instead of a MonadReader.
views		uses		View/fold after applying a function. views _2 (map toUpper) ("hello","world") == "WORLD" views each (Sum . succ . getSum) [Sum 1, Sum 2] == Sum 5
Control.Lens (Setting)
set / .~	<.~	assign / .=	<.=	Replace target(s) with value. set _2 "pluto" ("hello","world") == ("hello","pluto") set each 0 [1,2] == [0,0] set (setting Control.Arrow.second) 3 (1,2) == (1,3) ( set (upon snd) 3 $ (1,2) ) == (1,3) -- warning, here be dragons, see docu for upon <a href="http://ekmett.github.com/lens/Control-Lens-Lens.html#v:-60--60-.-126-"> <code> &lt;&lt;.~</code> </a> and <a href="http://ekmett.github.com/lens/Control-Lens-Lens.html#v:-60--60-.-61-"> <code> &lt;&lt;.= </code></a> return the old value.
over / %~	<%~	%=	<%=	Replace target(s) by applying function. over _2 (map toUpper) ("hello","world") over each (map toUpper) ["hello","world"] <<%~ and <<%= return the old value
id / %%~ / traverseOf		%%=		Update target(s) with an Applicative or auxiliary result ( (%%~) each $ \x -> if even x then Just . succ $ x else Nothing ) [2,4,6] ( (%%~) _2 $ \x -> if even x then Just . succ $ x else Nothing ) (2,4,6) traverseOf can replace (%%~) above but is less general. traverseOf applies to Over type, whereas (%%~) applies to Optical type. Over p is equivalent to Optical p (->)
Control.Lens.Fold / Control.Lens.Prism
review				Choose a branch of a sum type ( review _Right $ 1 ) == Right 1
preview / ^? / firstOf				Attempt to extract branch of a sum type. ( preview _Right . review _Right $ 1 ) == Just 1 works with view if a monoid... ( view _Right . Right $ [1,2,3] ) == [1,2,3] ( view _Right . Left $ [1,2,3] ) == ()
previews				preview after applying a function ( previews _Right (+1) . Right $ 1 ) == Just 2
toListOf / ^..				Return a list of the target(s) toListOf traverse ('a','b') == "b" toListOf each ('a','b') == "ab"
Control.Lens.Action (has everything here been removed from lens package??)
perform, performs ^!				Perform monadic action(s)
Control.Lens (Getting Indexed)
iview / ^@.		iuse		View the index and value of an IndexedGetter or IndexedLens. let mapHW = Data.Map.fromList [(1,"hello"),(2,"world")] mapHW ^@. iat 2 == (2,Just "world")
iviews		iuses		View a function of the index and value of an IndexedGetter into the current environment.
Control.Lens (Setting Indexed)
iset / .@~		.@=		Set target(s) with access to the index.
iover / %@~	<%@~	%@=	<%@=	Update target(s) with access to the index.
withIndex, itraverseOf, %%@~		%%@=		Update target(s) with an Applicative or auxiliary result with access to the index.
Control.Lens (math)
+~	<+~	+=	<+=	Add to target(s)
-~	<-~	-=	<-=	Subtract from target(s)
*~	<*~	*=	<*=	Multiply target(s)
//~	<//~	//=	<//=	Divide target(s)
^~	<^~	^=	<^=	Raise target(s) to a non-negative Integral power
^^~	<^^~	^^=	<^^=	Raise target(s) to an Integral power
**~	<**~	**=	<**=	Raise target(s) to an arbitrary power
Control.Lens (logic)
||~	<||~	||=	<||=	Logically or target(s)
&&~	<&&~	&&=	<&&=	Logically and target(s)
<>~	<<>~	<>=	<<>=	mappend to the target monoidal value(s)
Data.Bits.Lens
.|.~	<.|.~	.|.=	<.|.=	Bitwise or target(s)
.&.~	<.&.~	.&.=	<.&.=	Bitwise and target(s)
System.FilePath.Lens
</>~	<</>~	</>=	<</>=	Append a relative path to a FilePath
<.>~	<<.>~	<.>=	<<.>=	Append a file extension to a FilePath