# View Source Quark.SKI(Quark v2.3.3-doma)

The classic SKI system of combinators. `s` and `k` alone can be used to express any algorithm, though generally not efficiently.

# Link to this section Summary

## Functions

The identity combinator. Also aliased as `id`.

The constant ("Konstant") combinator. Returns the first argument unchanged, and discards the second argument.

The "substitution" combinator. Applies the last argument to the first two, and then the first two to each other.

Opposite of `first` (the `k` combinator).

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# i()

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The identity combinator. Also aliased as `id`.

``````iex> i(1)
1

iex> i("identity combinator")
"identity combinator"

iex> [1,2,3] |> id
[1,2,3]``````

# i(x)

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`@spec i(any()) :: any()`

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# k()

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The constant ("Konstant") combinator. Returns the first argument unchanged, and discards the second argument.

Can be used to repeatedly apply the same value in functions such as folds.

Aliased as `first` and `constant`.

## examples Examples

``````iex> k(1, 2)
1

"happy"

iex> Enum.reduce([1,2,3], [42], &k/2)
3

iex> Enum.reduce([1,2,3], [42], &constant/2)
3

iex> first(1,2)
1``````

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# k(x, y)

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`@spec k(any(), any()) :: any()`

# s()

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The "substitution" combinator. Applies the last argument to the first two, and then the first two to each other.

## examples Examples

``````iex> add = &(&1 + &2)
...> double = &(&1 * 2)
24``````

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# s(x, y, z)

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`@spec s((... -> any()), (... -> any()), any()) :: any()`

# second()

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Opposite of `first` (the `k` combinator).

While not strictly part of SKI, it's a common enough case.

Returns the second of two arguments. Can be used to repeatedly apply the same value in functions such as folds.

## examples Examples

``````iex> second(43, 42)
42

iex> Enum.reduce([1,2,3], [], &second/2)
[]``````
`@spec second(any(), any()) :: any()`