Create compose-functions.md

snippets/compose-functions.md

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+### Compose functions
+
+Use the `...rest` operator to gather all function arguments into an array. Return a function which takes
+a single argument and uses `Array.reduceRight()` to return the result of applying each function.
+
+```js
+const compose = (...fns) => n => fns.reduceRight((acc, fn) => fn(acc), n);
+/*
+const addOne = n => n + 1;
+const square = n => n * n;
+const double = n => n * 2;
+compose(addOne, square, double)(2) -> 17
+equivalent to: addOne(square(double(2)))
+*/
+```