Allow fn passed to Async.fromPromise to be partially applied (#475)

* Allow fn passed to Async.fromPromise to be partially applied

* Update docs to reflect changes to Async.fromPromise currying its input

* Update contributors

.all-contributorsrc

@@ -280,6 +280,15 @@
       "contributions": [
         "doc"
       ]
+    },
+    {
+      "login": "JamieDixon",
+      "name": "Jamie Dixon",
+      "avatar_url": "https://avatars2.githubusercontent.com/u/1519443?v=4",
+      "profile": "https://twitter.com/jamiedixon",
+      "contributions": [
+        "code"
+      ]
     }
   ],
   "repoType": "github",

README.md

@@ -236,6 +236,10 @@ Thanks goes to these wonderful people ([emoji key][emojis]):
     <td align="center"><a href="https://github.com/RichardForrester"><img src="https://avatars0.githubusercontent.com/u/12902182?v=4" width="100px;" alt=""/><br /><sub><b>RichardForrester</b></sub></a><br /><a href="https://github.com/evilsoft/crocks/commits?author=RichardForrester" title="Code">💻</a> <a href="https://github.com/evilsoft/crocks/commits?author=RichardForrester" title="Documentation">📖</a> <a href="https://github.com/evilsoft/crocks/commits?author=RichardForrester" title="Tests">⚠️</a></td>
     <td align="center"><a href="http://furkantunali.com"><img src="https://avatars2.githubusercontent.com/u/68406?v=4" width="100px;" alt=""/><br /><sub><b>Furkan Tunalı</b></sub></a><br /><a href="https://github.com/evilsoft/crocks/commits?author=JacopKane" title="Documentation">📖</a> <a href="#example-JacopKane" title="Examples">💡</a></td>
     <td align="center"><a href="https://github.com/sunwukonga"><img src="https://avatars3.githubusercontent.com/u/12194690?v=4" width="100px;" alt=""/><br /><sub><b>Paul Desmond Parker</b></sub></a><br /><a href="https://github.com/evilsoft/crocks/commits?author=sunwukonga" title="Documentation">📖</a></td>
+    <td align="center"><a href="https://github.com/area73"><img src="https://avatars3.githubusercontent.com/u/2030605?v=4" width="100px;" alt=""/><br /><sub><b>Rodrigo Erades</b></sub></a><br /><a href="https://github.com/evilsoft/crocks/commits?author=area73" title="Documentation">📖</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="http://jamie-dixon.co.uk"><img src="https://avatars2.githubusercontent.com/u/1519443?v=4" width="100px;" alt=""/><br /><sub><b>Jamie Dixon</b></sub></a><br /><a href="https://github.com/evilsoft/crocks/commits?author=JamieDixon" title="Code">💻</a></td>
   </tr>
 </table>
 

docs/src/pages/docs/crocks/Async.md

@@ -296,12 +296,12 @@ n.fork(log('rej'), log('res'))
 Async.fromPromise :: (* -> Promise a e) -> (* -> Async e a)
 ```
 
-Used to turn an "eager" `Promise` returning function, into a function that takes
-the same arguments but returns a "lazy" `Async` instance instead. Due to the
-lazy nature of `Async`, any curried interface will not be respected on the
-provided function. This can be solved by wrapping the resulting function
-with [`nAry`][nary], which will provide a curried function that will return the
-desired `Async`.
+Used to turn an "eager" `Promise` returning function into a function that takes
+the same arguments, but returns a "lazy" `Async` instance instead.
+
+The `Promise` returning function given to `fromPromise` is automatically curried,
+allowing you to partially apply the resulting function to its parameters until
+an `Async` type is returned.
 
 <!-- eslint-disable no-console -->
 <!-- eslint-disable no-sequences -->
@@ -311,7 +311,6 @@ import Async from 'crocks/Async'
 
 import ifElse from 'crocks/logic/ifElse'
 import isNumber from 'crocks/predicates/isNumber'
-import nAry from 'crocks/helpers/nAry'
 
 const { fromPromise } = Async
 
@@ -334,7 +333,7 @@ safeProm(isNumber, '34')
 
 // safeAsync :: (a -> Boolean) -> a -> Async a a
 const safeAsync =
-  nAry(2, fromPromise(safeProm))
+  fromPromise(safeProm)
 
 // numAsync :: a -> Async a Number
 const numAsync =
@@ -380,8 +379,8 @@ As such, the need for binding may arise. `fromNode` provides a second, optional
 argument that takes the context that will be used to bind the function being
 wrapped.
 
-Like [`fromPromise`](#frompromise), any curried interface will not be respected.
-If a curried interface is needed then [`nAry`][nary] can be used.
+Any curried interface will not be respected and if a curried interface is needed 
+then [`nAry`][nary] can be used.
 
 <!-- eslint-disable no-console -->
 <!-- eslint-disable no-sequences -->

src/Async/Async.spec.js

@@ -150,7 +150,6 @@ test('Async fromPromise', t => {
   t.throws(fork(true), err, 'throws when true is returned from promise function')
   t.throws(fork([]), err, 'throws when an array is returned from promise function')
   t.throws(fork({}), err, 'throws when an object is returned from promise function')
-  t.throws(fork(unit), err, 'throws when an object is returned from promise function')
 
   t.end()
 })
@@ -170,6 +169,24 @@ test('Async fromPromise resolution', t => {
   Async.fromPromise(resProm)(val).fork(rej(val), res(val))
 })
 
+test('Async fromPromise resolution with partially applied function', t => {
+  t.plan(2)
+
+  const val1 = 1
+  const val2 = 2
+
+  const val = val1 + val2
+
+  const rejProm = x => y => new Promise((_, rej) => rej(x + y))
+  const resProm = x => y => new Promise((res) => res(x + y))
+
+  const rej = y => x => t.equal(x, y, 'rejects a rejected Promise')
+  const res = y => x => t.equal(x, y, 'resolves a resolved Promise')
+
+  Async.fromPromise(rejProm)(val1)(val2).fork(rej(val), res(val))
+  Async.fromPromise(resProm)(val1)(val2).fork(rej(val), res(val))
+})
+
 test('Async fromNode', t => {
   const resCPS = (x, cf) => cf(null, x)
 

src/Async/index.js

@@ -11,6 +11,7 @@ const fl = require('../core/flNames')
 
 const array = require('../core/array')
 const compose = require('../core/compose')
+const curry = require('../core/curry')
 const once = require('../core/once')
 const unit = require('../core/_unit')
 
@@ -62,11 +63,18 @@ function fromPromise(fn) {
     throw new TypeError('Async.fromPromise: Promise returning function required')
   }
 
+  const _fn = curry(fn)
+
   return function() {
     const promiseArgs = arguments
 
+    const promise = _fn.apply(null, promiseArgs)
+
+    if (isFunction(promise)) {
+      return fromPromise(promise)
+    }
+
     return Async(function(reject, resolve) {
-      const promise = fn.apply(null, promiseArgs)
 
       if(!isPromise(promise)) {
         throw new TypeError('Async.fromPromise: Promise returning function required')