Add functional API.

README.md

@@ -228,6 +228,28 @@ Closed channels always return `undefined` immediately.
 
 #### slice(start, end) -> Channel
 
+### Functional API
+
+There is a parallel API to support functional-style programming.  Every channel
+method is also available as an independent function in the `Channel` namespace
+that takes a channel as the final argument.  For example, `slice` can be called
+in either of the following two ways:
+
+```JavaScript
+// method
+channel.slice(10)
+
+// function
+Channel.slice(10, Infinity, channel)
+```
+
+You can also use partial application to pass the channel in later:
+
+```JavaScript
+const skipTen = Channel.slice(10, Infinity)
+skipTen(channel)
+```
+
 # Contributing
 
 Please [submit an issue](https://github.com/NodeGuy/channel/issues/new) if you

lib/index.js

@@ -311,4 +311,28 @@ Channel.select = (...methodPromises) => {
   return promise
 }
 
+// functional interface allowing full or partial application
+//
+// Channel.slice(10, Infinity, channel)
+//
+// or
+//
+// const skipTen = Channel.slice(10, Infinity)
+// skipTen(channel)
+
+const channel = Channel()
+const methods = Object.keys(channel).concat(Object.keys(channel.readOnly()))
+
+methods.forEach((method) => {
+  Channel[method] = (...args) => {
+    const arity = method === `slice`
+      ? 3
+      : channel[method].length
+
+    return args.length >= arity
+      ? args[arity - 1][method](...args.slice(0, arity - 1))
+      : (channel) => channel[method](...args)
+  }
+})
+
 module.exports = Object.freeze(Channel)

test/index.js

@@ -99,6 +99,45 @@ describe(`Channel`, function () {
         break
     }
   })
+
+  describe(`functional interface`, async function () {
+    describe(`map`, function () {
+      it(`full application`, async function () {
+        assert.deepEqual(
+          await toArray(Channel.map(
+            (value) => value.toUpperCase(),
+            Channel.of(`a`, `b`, `c`)
+          )),
+          [`A`, `B`, `C`]
+        )
+      })
+
+      it(`partial application`, async function () {
+        assert.deepEqual(
+          await toArray(Channel.map((value) =>
+            value.toUpperCase())(Channel.of(`a`, `b`, `c`))
+          ),
+          [`A`, `B`, `C`]
+        )
+      })
+    })
+
+    describe(`slice`, function () {
+      it(`full application`, async function () {
+        assert.deepEqual(
+          await toArray(Channel.slice(1, 4, Channel.of(0, 1, 2, 3, 4))),
+          [1, 2, 3]
+        )
+      })
+
+      it(`partial application`, async function () {
+        assert.deepEqual(
+          await toArray(Channel.slice(1, 4)(Channel.of(0, 1, 2, 3, 4))),
+          [1, 2, 3]
+        )
+      })
+    })
+  })
 })
 
 describe(`Channel object`, function () {
@@ -143,7 +182,9 @@ describe(`Channel object`, function () {
 
   it(`filter`, async function () {
     assert.deepEqual(
-      await toArray(Channel.of(0, 1, 2, 3, 4, 5).filter(x => x % 2 !== 0)),
+      await toArray(Channel.of(0, 1, 2, 3, 4, 5)
+        .filter((value) => value % 2 !== 0)
+      ),
       [1, 3, 5]
     )
   })
@@ -165,7 +206,9 @@ describe(`Channel object`, function () {
 
   it(`map`, async function () {
     assert.deepEqual(
-      await toArray(Channel.of(`a`, `b`, `c`).map(x => x.toUpperCase())),
+      await toArray(Channel.of(`a`, `b`, `c`)
+        .map((value) => value.toUpperCase())
+      ),
       [`A`, `B`, `C`]
     )
   })