< -package:ghc-lib-parser package:hledger-web

Replace all locations in the input with the same value. The default definition is fmap . const, but this may be overridden with a more efficient version.

Strict version of <$>.

An infix synonym for fmap. The name of this operator is an allusion to $. Note the similarities between their types:

($)  ::              (a -> b) ->   a ->   b
(<$>) :: Functor f => (a -> b) -> f a -> f b

Whereas $ is function application, <$> is function application lifted over a Functor.

Examples

Convert from a Maybe Int to a Maybe String using show:

>>> show <$> Nothing
Nothing

>>> show <$> Just 3
Just "3"

Convert from an Either Int Int to an Either Int String using show:

>>> show <$> Left 17
Left 17

>>> show <$> Right 17
Right "17"

Double each element of a list:

>>> (*2) <$> [1,2,3]
[2,4,6]

Apply even to the second element of a pair:

>>> even <$> (2,2)
(2,True)

Sequence actions, discarding the value of the second argument.

Sequential application. A few functors support an implementation of <*> that is more efficient than the default one.

Example

Used in combination with (<$>), (<*>) can be used to build a record.

>>> data MyState = MyState {arg1 :: Foo, arg2 :: Bar, arg3 :: Baz}

>>> produceFoo :: Applicative f => f Foo

>>> produceBar :: Applicative f => f Bar

>>> produceBaz :: Applicative f => f Baz

>>> mkState :: Applicative f => f MyState

>>> mkState = MyState <$> produceFoo <*> produceBar <*> produceBaz

Check if value is in given list.

Examples

selectUsers :: MonadIO m => ReaderT SqlBackend m [Entity User]
selectUsers = selectList [UserAge <-. [40, 41]] []

The above query when applied on dataset-1, will produce this:

+-----+-----+-----+
|id   |name |age  |
+-----+-----+-----+
|1    |SPJ  |40   |
+-----+-----+-----+
|2    |Simon|41   |
+-----+-----+-----+

selectSPJ :: MonadIO m => ReaderT SqlBackend m [Entity User]
selectSPJ = selectList [UserAge <-. [40]] []

The above query when applied on dataset-1, will produce this:

+-----+-----+-----+
|id   |name |age  |
+-----+-----+-----+
|1    |SPJ  |40   |
+-----+-----+-----+

Less-than check.

Examples

selectLessAge :: MonadIO m => ReaderT SqlBackend m [Entity User]
selectLessAge = selectList [UserAge <. 41 ] []

The above query when applied on dataset-1, will produce this:

+-----+-----+-----+
|id   |name |age  |
+-----+-----+-----+
|1    |SPJ  |40   |
+-----+-----+-----+

Less-than or equal check.

Examples

selectLessEqualAge :: MonadIO m => ReaderT SqlBackend m [Entity User]
selectLessEqualAge = selectList [UserAge <=. 40 ] []

The above query when applied on dataset-1, will produce this:

+-----+-----+-----+
|id   |name |age  |
+-----+-----+-----+
|1    |SPJ  |40   |
+-----+-----+-----+

Right-to-left composition of Kleisli arrows. (>=>), with the arguments flipped. Note how this operator resembles function composition (.):

(.)   ::            (b ->   c) -> (a ->   b) -> a ->   c
(<=<) :: Monad m => (b -> m c) -> (a -> m b) -> a -> m c

An associative operation.

>>> [1,2,3] <> [4,5,6]
[1,2,3,4,5,6]

Check if value is not in given list.

Examples

selectSimon :: MonadIO m => ReaderT SqlBackend m [Entity User]
selectSimon = selectList [UserAge /<-. [40]] []

The above query when applied on dataset-1, will produce this:

+-----+-----+-----+
|id   |name |age  |
+-----+-----+-----+
|2    |Simon|41   |
+-----+-----+-----+

Same as >>=, but with the arguments interchanged.