# Lampiran C: Utilitas Pointfree

Dalam lampiran ini, Anda akan menemukan beberapa implementasi JavaScript dasar dari berbagai fungsi yang dijelaskan dalam buku ini.

Ingatlah bahwa implementasi ini mungkin bukan implementasi tercepat atau paling efisien di luar sana; mereka dibuat *hanya untuk tujuan pendidikan*.

Untuk menemukan fungsi yang lebih siap produksi, lihat [ramda](https://ramdajs.com/), [lodash](https://lodash.com/), atau [folktale](http://folktale.origamitower.com/).

Perhatikan bahwa fungsi mengacu pada `curry` & `compose` fungsi yang didefinisikan dalam [Lampiran A](/belajar-functional-programming-javascript/appendix_a-id.md).

## add

```javascript
// add :: Number -> Number -> Number
const add = curry((a, b) => a + b);
```

## append

```javascript
// append :: String -> String -> String
const append = flip(concat);
```

## chain

```javascript
// chain :: Monad m => (a -> m b) -> m a -> m b
const chain = curry((fn, m) => m.chain(fn));
```

## concat

```javascript
// concat :: String -> String -> String
const concat = curry((a, b) => a.concat(b));
```

## eq

```javascript
// eq :: Eq a => a -> a -> Boolean
const eq = curry((a, b) => a === b);
```

## filter

```javascript
// filter :: (a -> Boolean) -> [a] -> [a]
const filter = curry((fn, xs) => xs.filter(fn));
```

## flip

```javascript
// flip :: (a -> b -> c) -> b -> a -> c
const flip = curry((fn, a, b) => fn(b, a));
```

## forEach

```javascript
// forEach :: (a -> ()) -> [a] -> ()
const forEach = curry((fn, xs) => xs.forEach(fn));
```

## head

```javascript
// head :: [a] -> a
const head = (xs) => xs[0];
```

## intercalate

```javascript
// intercalate :: String -> [String] -> String
const intercalate = curry((str, xs) => xs.join(str));
```

## join

```javascript
// join :: Monad m => m (m a) -> m a
const join = (m) => m.join();
```

## last

```javascript
// last :: [a] -> a
const last = (xs) => xs[xs.length - 1];
```

## map

```javascript
// map :: Functor f => (a -> b) -> f a -> f b
const map = curry((fn, f) => f.map(fn));
```

## match

```javascript
// match :: RegExp -> String -> Boolean
const match = curry((re, str) => re.test(str));
```

## prop

```javascript
// prop :: String -> Object -> a
const prop = curry((p, obj) => obj[p]);
```

## reduce

```javascript
// reduce :: (b -> a -> b) -> b -> [a] -> b
const reduce = curry((fn, zero, xs) => xs.reduce(fn, zero));
```

## replace

```javascript
// replace :: RegExp -> String -> String -> String
const replace = curry((re, rpl, str) => str.replace(re, rpl));
```

## reverse

```javascript
// reverse :: [a] -> [a]
const reverse = (x) =>
  Array.isArray(x) ? x.reverse() : x.split("").reverse().join("");
```

## safeHead

```javascript
// safeHead :: [a] -> Maybe a
const safeHead = compose(Maybe.of, head);
```

## safeLast

```javascript
// safeLast :: [a] -> Maybe a
const safeLast = compose(Maybe.of, last);
```

## safeProp

```javascript
// safeProp :: String -> Object -> Maybe a
const safeProp = curry((p, obj) => compose(Maybe.of, prop(p))(obj));
```

## sequence

```javascript
// sequence :: (Applicative f, Traversable t) => (a -> f a) -> t (f a) -> f (t a)
const sequence = curry((of, f) => f.sequence(of));
```

## sortBy

```javascript
// sortBy :: Ord b => (a -> b) -> [a] -> [a]
const sortBy = curry((fn, xs) =>
  xs.sort((a, b) => {
    if (fn(a) === fn(b)) {
      return 0;
    }

    return fn(a) > fn(b) ? 1 : -1;
  })
);
```

## split

```javascript
// split :: String -> String -> [String]
const split = curry((sep, str) => str.split(sep));
```

## take

```javascript
// take :: Number -> [a] -> [a]
const take = curry((n, xs) => xs.slice(0, n));
```

## toLowerCase

```javascript
// toLowerCase :: String -> String
const toLowerCase = (s) => s.toLowerCase();
```

## toString

```javascript
// toString :: a -> String
const toString = String;
```

## toUpperCase

```javascript
// toUpperCase :: String -> String
const toUpperCase = (s) => s.toUpperCase();
```

## traverse

```javascript
// traverse :: (Applicative f, Traversable t) => (a -> f a) -> (a -> f b) -> t a -> f (t b)
const traverse = curry((of, fn, f) => f.traverse(of, fn));
```

## unsafePerformIO

```javascript
// unsafePerformIO :: IO a -> a
const unsafePerformIO = (io) => io.unsafePerformIO();
```


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