adds lens function (#61)

* adds lens function
* use v0.42.0 std temporarily

Author: Tomasz Gałkowski

CHANGELOG.md

@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+- adds lens function
+
 ## [0.3.0] - 2020-05-14
 
 ### Added
@@ -90,7 +93,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - reverse function
 - tail function
 
-[unreleased]: https://github.com/galkowskit/denofun/compare/0.3.0...HEAD
+[Unreleased]: https://github.com/galkowskit/denofun/compare/0.3.0...HEAD
 [0.3.0]: https://github.com/galkowskit/denofun/compare/v0.2.0...0.3.0
 [v0.2.0]: https://github.com/galkowskit/denofun/compare/v0.1.0...v0.2.0
 [v0.1.0]: https://github.com/galkowskit/denofun/releases/tag/v0.1.0

README.md

@@ -441,6 +441,24 @@ last([1, "test", 3]); // => 3
 last("hello world!"); // => "!"
 ```
 
+### lens
+
+**lens** lens returns a special lens object that can be used as a function setter/getter.
+
+```typescript
+import lens from "https://deno.land/x/denofun/lens.ts";
+
+const car = Object.freeze({
+  make: "Toyota",
+  model: "GT86",
+});
+
+const getCarModel = (data: { make: string, model: string }) => data.model;
+const setCarModel = (data: { make: string, model: string }, value: string) => ({ ...data, model: value });
+
+const carModelLens = lens(getCarModel, setCarModel); // => Lens<Car, string>
+```
+
 ### map
 
 **map** applies a function to each element of the array, returns the array of results.
@@ -602,7 +620,29 @@ reverse([1, 2, 3, 4, 5]); // => [5, 4, 3, 2, 1]
 reverse("hello world!"); // => ["!dlrow olleh"]
 ```
 
-**slice** return a given slice of an array or string (wrapper over Array.prototype.slice)
+### set
+
+**set** uses a provided lens, copies the provided object with a changed value.
+
+```typescript
+import lens from "https://deno.land/x/denofun/lens.ts";
+import set from "https://deno.land/x/denofun/set.ts";
+
+const car = Object.freeze({
+  make: "Toyota",
+  model: "GT86",
+});
+
+const getCarModel = (data: { make: string, model: string }) => data.model;
+const setCarModel = (data: { make: string, model: string }, value: string) => ({ ...data, model: value });
+
+const carModelLens = lens(getCarModel, setCarModel);
+set(carModelLens, car, "Mirai"); // => { make: "Toyota", model: "Mirai" }
+```
+
+### slice
+
+**slice** return a given slice of an array or string (wrapper over Array.prototype.slice).
 
 ```typescript
 import slice from "https://deno.land/x/denofun/slice.ts";
@@ -676,6 +716,26 @@ const car = { make: "Alfa Romeo", model: "Giulia" };
 values(car); // => ["make", "model"]
 ```
 
+### view
+
+**view** uses a lens to get value from an object.
+
+```typescript
+import lens from "https://deno.land/x/denofun/lens.ts";
+import view from "https://deno.land/x/denofun/view.ts";
+
+const car = Object.freeze({
+  make: "Toyota",
+  model: "GT86",
+});
+
+const getCarModel = (data: { make: string, model: string }) => data.model;
+const setCarModel = (data: { make: string, model: string }, value: string) => ({ ...data, model: value });
+
+const carModelLens = lens(getCarModel, setCarModel);
+view(carModelLens, car); // => "GT86"
+```
+
 ## For Developers
 
 If you want to contribute to Denofun:

lib/lens.ts

@@ -0,0 +1,19 @@
+export type Lens<T, V> = {
+  getter: (data: T) => V;
+  setter: (data: T, value: V) => T;
+};
+
+/**
+ * **lens** lens returns a special lens object that can be used as a function setter/getter
+ * @param getterFn
+ * @param setterFn
+ */
+export default function lens<T, V>(
+  getterFn: (data: T) => V,
+  setterFn: (data: T, value: V) => T,
+): Lens<T, V> {
+  return {
+    getter: getterFn,
+    setter: setterFn,
+  };
+}

lib/set.ts

@@ -0,0 +1,11 @@
+import { Lens } from "./lens.ts";
+
+/**
+ * **set** uses a provided lens, copies the provided object with a changed value
+ * @param lens {Lens} the lens that will be used
+ * @param obj the object to be copied with the changed data
+ * @param value the value to be used by the lens
+ */
+export default function set<T, V>(lens: Lens<T,V>, obj: T, value: V): T {
+    return lens.setter(obj, value);
+}

lib/view.ts

@@ -0,0 +1,10 @@
+import { Lens } from "../lib/lens.ts";
+
+/**
+ * **view** uses a lens to get value from an object
+ * @param lens {Lens} a lens created by _lens_ function
+ * @param obj data from which to get the value
+ */
+export default function view<T, V>(lens: Lens<T, V>, obj: T): V {
+    return lens.getter(obj);
+}

test/lens_test.ts

@@ -0,0 +1,25 @@
+import { assertEquals } from "https://deno.land/std@v0.42.0/testing/asserts.ts";
+
+import lens from "../lib/lens.ts";
+
+const car = Object.freeze({
+  make: "Toyota",
+  model: "GT86",
+});
+
+const getCarModel = (data: { make: string, model: string }) => data.model;
+const setCarModel = (data: { make: string, model: string }, value: string) => ({ ...data, model: value });
+
+const carModelLens = lens(getCarModel, setCarModel);
+
+Deno.test({
+  name: "lens",
+  fn(): void {
+    assertEquals(typeof lens, "function");
+    assertEquals(typeof carModelLens, "object");
+    assertEquals(typeof carModelLens.getter, "function");
+    assertEquals(typeof carModelLens.setter, "function");
+    assertEquals(carModelLens.getter(car), "GT86");
+    assertEquals(carModelLens.setter(car, "Mirai"), { make: "Toyota", model: "Mirai" });
+  },
+});

test/set_test.ts

@@ -0,0 +1,22 @@
+import { assertEquals } from "https://deno.land/std@v0.42.0/testing/asserts.ts";
+
+import lens from "../lib/lens.ts";
+import set from "../lib/set.ts";
+
+const car = Object.freeze({
+  make: "Toyota",
+  model: "GT86",
+});
+
+const getCarModel = (data: { make: string, model: string }) => data.model;
+const setCarModel = (data: { make: string, model: string }, value: string) => ({ ...data, model: value });
+
+const carModelLens = lens(getCarModel, setCarModel);
+
+Deno.test({
+  name: "set",
+  fn(): void {
+      assertEquals(typeof set, "function");
+      assertEquals(set(carModelLens, car, "Mirai"), { make: "Toyota", model: "Mirai" });
+  },
+});

test/view_test.ts

@@ -0,0 +1,22 @@
+import { assertEquals } from "https://deno.land/std@v0.42.0/testing/asserts.ts";
+
+import lens from "../lib/lens.ts";
+import view from "../lib/view.ts";
+
+const car = Object.freeze({
+  make: "Toyota",
+  model: "GT86",
+});
+
+const getCarModel = (data: { make: string, model: string }) => data.model;
+const setCarModel = (data: { make: string, model: string }, value: string) => ({ ...data, model: value });
+
+const carModelLens = lens(getCarModel, setCarModel);
+
+Deno.test({
+  name: "view",
+  fn(): void {
+      assertEquals(typeof view, "function");
+      assertEquals(view(carModelLens, car), "GT86");
+  },
+});