# Data.Function

- Package
- purescript-prelude
- Repository
- purescript/purescript-prelude

### #flipSource

`flip :: forall a b c. (a -> b -> c) -> b -> a -> c`

Flips the order of the arguments to a function of two arguments.

```
flip const 1 2 = const 2 1 = 2
```

### #constSource

`const :: forall a b. a -> b -> a`

Returns its first argument and ignores its second.

```
const 1 "hello" = 1
```

### #applySource

`apply :: forall a b. (a -> b) -> a -> b`

Applies a function to an argument. This is primarily used as the operator
`($)`

which allows parentheses to be omitted in some cases, or as a
natural way to apply a chain of composed functions to a value.

### #($)Source

Operator alias for Data.Function.apply *(right-associative / precedence 0)*

Applies a function to an argument: the reverse of `(#)`

.

```
length $ groupBy productCategory $ filter isInStock $ products
```

is equivalent to:

```
length (groupBy productCategory (filter isInStock products))
```

Or another alternative equivalent, applying chain of composed functions to a value:

```
length <<< groupBy productCategory <<< filter isInStock $ products
```

### #applyFlippedSource

`applyFlipped :: forall a b. a -> (a -> b) -> b`

Applies an argument to a function. This is primarily used as the `(#)`

operator, which allows parentheses to be ommitted in some cases, or as a
natural way to apply a value to a chain of composed functions.

### #(#)Source

Operator alias for Data.Function.applyFlipped *(left-associative / precedence 1)*

Applies an argument to a function: the reverse of `($)`

.

```
products # filter isInStock # groupBy productCategory # length
```

is equivalent to:

```
length (groupBy productCategory (filter isInStock products))
```

Or another alternative equivalent, applying a value to a chain of composed functions:

```
products # filter isInStock >>> groupBy productCategory >>> length
```

### #onSource

`on :: forall a b c. (b -> b -> c) -> (a -> b) -> a -> a -> c`

The `on`

function is used to change the domain of a binary operator.

For example, we can create a function which compares two records based on the values of their `x`

properties:

```
compareX :: forall r. { x :: Number | r } -> { x :: Number | r } -> Ordering
compareX = compare `on` _.x
```

## Re-exports from **Control.**Category

### #compose

`compose :: forall b c d a. Semigroupoid a => a c d -> a b c -> a b d`

- Modules
- Control.
Applicative - Control.
Apply - Control.
Bind - Control.
Category - Control.
Monad - Control.
Semigroupoid - Data.
Boolean - Data.
BooleanAlgebra - Data.
Bounded - Data.
CommutativeRing - Data.
Eq - Data.
EuclideanRing - Data.
Field - Data.
Function - Data.
Functor - Data.
HeytingAlgebra - Data.
NaturalTransformation - Data.
Ord - Data.
Ord. Unsafe - Data.
Ordering - Data.
Ring - Data.
Semigroup - Data.
Semiring - Data.
Show - Data.
Unit - Data.
Void - Prelude