Introduce fromClass isomorphism to deal with non-Objects

This partially addresses issue #40.

src/partial.lenses.js

@@ -653,6 +653,17 @@ export const iso =
 
 // Isomorphisms and combinators
 
+export const fromClass = Class => {
+  const toClass = x => isObject(x)
+    ? Object.assign(Object.create(Class.prototype), x)
+    : void 0
+  return (F, xi2yF, x, i) =>
+    (0,F.map)(toClass,
+              xi2yF(Object.getPrototypeOf(x).constructor === Class
+                    ? Object.assign({}, x)
+                    : void 0, i))
+}
+
 export const identity = (_F, xi2yF, x, i) => xi2yF(x, i)
 
 export const inverse = iso => (F, xi2yF, x, i) =>

test/core.js

@@ -122,5 +122,6 @@ export const getInverse = R.curry((i, s) => set(i, s, undefined))
 
 export const iso = lens
 
+export const fromClass = L.fromClass
 export const identity = iso(R.identity, R.identity)
 export const inverse = i => iso(getInverse(i), get(i))

test/tests.js

@@ -535,6 +535,17 @@ describe("L.branch", () => {
   testEq('L.set(L.branch({a: ["x",0], b: []}), 0, null)', {a:{x:[0]},b:0})
 })
 
+function XYZ(x,y,z) {
+  this.x = x
+  this.y = y
+  this.z = z
+}
+
+describe("L.fromClass", () => {
+  testEq('L.get([L.fromClass(XYZ), "y"], new XYZ(1,2,3))', 2)
+  testEq('L.set([L.fromClass(XYZ), "x"], -1, new XYZ(1,2,3))', new XYZ(-1,2,3))
+})
+
 describe("indexing", () => {
   testEq('L.modify(L.identity, (x, i) => [typeof x, typeof i], 0)',
          ["number", "undefined"])

test/types.js

@@ -148,5 +148,6 @@ export const iso = T.fn([T.fn([T_maybeData], T_maybeData),
                          T.fn([T_maybeData], T_maybeData)],
                         T_isomorphism)
 
+export const fromClass = T.fn([T.any], T_isomorphism)
 export const identity = T_isomorphism
 export const inverse = T.fn([T_isomorphism], T_isomorphism)