# Quark.SKI (Quark v2.3.2) View Source

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

See `Quark.SKI.k/2`

.

The identity combinator. Also aliased as `id`

.

See `Quark.SKI.i/1`

.

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).

# Link to this section Functions

See `Quark.SKI.k/2`

.

See `Quark.SKI.k/2`

.

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]
```

## Specs

See `Quark.SKI.i/1`

.

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

```
iex> k(1, 2)
1
iex> k("happy", "sad")
"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
```

## Specs

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

## Examples

```
iex> add = &(&1 + &2)
...> double = &(&1 * 2)
...> s(add, double, 8)
24
```

## Specs

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

```
iex> second(43, 42)
42
iex> Enum.reduce([1,2,3], [], &second/2)
[]
```