Add coyoneda example

Author: dmitriz

examples/coyoneda.js

@@ -0,0 +1,76 @@
+// Video: https://www.youtube.com/watch?v=WH5BrkzGgQY
+
+const daggy = require('daggy')
+const compose = (f, g) => x => f(g(x))
+const id = x => x
+
+
+//===============Define Coyoneda=========
+
+// create constructor with props 'x' and 'f'
+// 'x' is our value, 'f' is a function
+const Coyoneda = daggy.tagged('x', 'f')
+
+// map composes the function
+Coyoneda.prototype.map = function(f) {
+  return Coyoneda(this.x, compose(f, this.f))
+}
+
+Coyoneda.prototype.lower = function() {
+  return this.x.map(this.f)
+}
+
+// lift starts off Coyoneda with the 'id' function
+Coyoneda.lift = x => Coyoneda(x, id)
+
+
+//===============Map over a non-Functor - Set =========
+
+// Set does not have a 'map' method
+const set = new Set([1, 1, 2, 3, 3, 4])
+
+console.log("Set is: ", set)
+
+// Wrap set into Coyoneda with 'id' function
+const coyo_result = Coyoneda.lift(set)
+  .map(x => x + 1)
+  .map(x => `${x}!`)
+
+console.log("Mapped over Set is: ", coyo_result)
+
+// equivalent to buildUpFn = coyo_result.f, our_set = coyo_result.x
+const {f: builtUpFn, x: our_set} = coyo_result
+
+console.log("builtUpFn is: ", builtUpFn, "; our_set is: ", our_set)
+
+our_set
+  .forEach(n => console.log(builtUpFn(n)))
+// 2!
+// 3!
+// 4!
+// 5!
+
+
+//===============Lift a functor in (Array) and achieve Loop fusion=========
+Coyoneda.lift([1,2,3])
+  .map(x => x * 2)
+  .map(x => x - 1)
+  .lower()
+// [ 1, 3, 5 ]
+
+
+//===============Make Any Type a Functor=========
+// Any object becomes a functor when placed in Coyoneda
+
+const Container = daggy.tagged('x')
+
+const tunacan = Container("tuna")
+
+const res = Coyoneda.lift(tunacan)
+  .map(x => x.toUpperCase())
+  .map(x => x + '!')
+
+
+const {f: fn, x: can} = res
+console.log(fn(can.x))
+// TUNA!

examples/package.json

@@ -1,5 +1,6 @@
 {
   "dependencies": {
+    "daggy": "^0.0.1",
     "futurize": "^1.0.2"
   }
 }

examples/yarn.lock

@@ -2,6 +2,10 @@
 # yarn lockfile v1
 
 
+daggy@^0.0.1:
+  version "0.0.1"
+  resolved "https://registry.yarnpkg.com/daggy/-/daggy-0.0.1.tgz#ae9c932c9f7136e655a04afb21e8baadfd0d3707"
+
 futurize@^1.0.2:
   version "1.0.2"
   resolved "https://registry.yarnpkg.com/futurize/-/futurize-1.0.2.tgz#7cce73efa3eae3a5ce27a3fce69889d478e9ce38"