view -package:heap

View the value pointed to by a Getter, Iso or Lens or the result of folding over all the results of a Fold or Traversal that points at a monoidal value.

view . to ≡ id

>>> view (to f) a
f a

>>> view _2 (1,"hello")
"hello"

>>> view (to succ) 5
6

>>> view (_2._1) ("hello",("world","!!!"))
"world"

As view is commonly used to access the target of a Getter or obtain a monoidal summary of the targets of a Fold, It may be useful to think of it as having one of these more restricted signatures:

view ::             Getter s a     -> s -> a
view :: Monoid m => Fold s m       -> s -> m
view ::             Iso' s a       -> s -> a
view ::             Lens' s a      -> s -> a
view :: Monoid m => Traversal' s m -> s -> m

In a more general setting, such as when working with a Monad transformer stack you can use:

view :: MonadReader s m             => Getter s a     -> m a
view :: (MonadReader s m, Monoid a) => Fold s a       -> m a
view :: MonadReader s m             => Iso' s a       -> m a
view :: MonadReader s m             => Lens' s a      -> m a
view :: (MonadReader s m, Monoid a) => Traversal' s a -> m a

view is a synonym for (^.):

>>> view _1 (1, 2)
1

The reason it's not in Lens.Micro is that view in lens has a more general signature:

view :: MonadReader s m => Getting a s a -> m a

So, you would be able to use this view with functions, but not in various reader monads. For most people this shouldn't be an issue; if it is for you, use view from microlens-mtl.

create a view on a given bytearray This function update the offset and the size in order to guarantee:

• offset >= 0
• size >= 0
• offset < length
• size =< length - offset

Gets a value out of a structure using a getter.

view is a synonym for (^.), generalised for MonadReader (we are able to use it instead of (^.) since functions are instances of the MonadReader class):

>>> view _1 (1, 2)
1

When you're using Reader for config and your config type has lenses generated for it, most of the time you'll be using view instead of asks:

doSomething :: (MonadReader Config m) => m Int
doSomething = do
thingy        <- view setting1  -- same as “asks (^. setting1)”
anotherThingy <- view setting2
...

View the value pointed to by a getter. If you want to view a type-modifying optic that is insufficiently polymorphic to be type-preserving, use getting.

Run a Shell to completion, printing any unused values

view :: Getter s t a b -> s -> a

Demote a lens or getter to a projection function.

view :: Monoid a => Fold s t a b -> s -> a

Returns the monoidal summary of a traversal or a fold.

View function for inspecting the first instruction.

A convenient function for using view patterns when dispatching variants. For example:

myShow :: Var ("y" '::= String :| "x" '::= Int :| Empty) -> String
myShow (view x -> Just n) = "Int of "++show n
myShow (view y -> Just s) = "String of "++s

Set parameters of viewing a surface graph. See info:gnuplot/view

Deprecated: Use viewAssign or the Empty and :> patterns instead.

Combinator for the <view /> element.

Ask for part of read-only state.

O(w). Set focus to the workspace with index 'i'. If the index is out of range, return the original StackSet. Xinerama: If the workspace is not visible on any Xinerama screen, it becomes the current screen. If it is in the visible list, it becomes current.

Explicitly set a diagram's bounding box, by giving the coordinates of the upper left and lower right corners (keeping in mind that the positive y-axis points downwards). Particularly useful for applying to the top-level diagram in order to only view a portion of it in the rendered output.

A version of W.view that tracks the need to refresh.

Function to draw View