feat(curry): add curry function with tests (#194)

I have added a new utility function that allows for the creation of a curried version of a function provided. I also added a basic test to verify that the function behaves as expected.

Resolves #193

Author: ericArbour

src/curry.js

@@ -0,0 +1,25 @@
+export default curry
+
+/*
+ * Original Source: https://stackoverflow.com/a/14045565/6121634
+ * Updated to ES6 format to meet style guides via:
+ * https://github.com/getify/Functional-Light-JS/blob/master/manuscript/ch3.md/#some-now-some-later
+ *
+ * This utility function takes a function as a parameter and returns a curried version of the function.
+ *
+ * @param {Function} func - The function to be curried
+ * @return {Function} - The curried version of the initially provided function
+ */
+function curry(fn, arity = fn.length) {
+  return (function nextCurried(prevArgs) {
+    return function curried(nextArg) {
+      const args = [...prevArgs, nextArg]
+
+      if (args.length >= arity) {
+        return fn(...args)
+      } else {
+        return nextCurried(args)
+      }
+    }
+  })([])
+}

src/index.js

@@ -70,6 +70,7 @@ import lcm from './lcm'
 import occurrences from './occurrences'
 import getMiddle from './getMiddle'
 import debounce from './debounce'
+import curry from './curry'
 
 export {
   reverseArrayInPlace,
@@ -144,4 +145,5 @@ export {
   occurrences,
   getMiddle,
   debounce,
+  curry,
 }

test/curry.test.js

@@ -0,0 +1,14 @@
+import test from 'ava'
+import {curry} from '../src'
+
+test('Returns a curried version of the provided function', t => {
+  function addOrConcat(one, two, three) {
+    return one + two + three
+  }
+  const expected = addOrConcat('foo', 'bar', 'baz')
+  const curried = curry(addOrConcat)
+  const withFirstArg = curried('foo')
+  const withSecondArg = withFirstArg('bar')
+  const actual = withSecondArg('baz')
+  t.deepEqual(actual, expected)
+})