feat: add Logger monad (#166)

Author: patrickmichalina

src/logger/logger.spec.ts

@@ -0,0 +1,76 @@
+import { Logger } from './logger'
+
+describe(Logger.name, () => {
+
+  it('should construct', () => {
+    const sut = new Logger([], '')
+
+    expect(sut).toBeInstanceOf(Logger)
+  })
+
+  it('should flatMap', () => {
+    const sut = new Logger(['starting with 100'], 100)
+      .flatMap(b => new Logger(['adding 3'], b + 3))
+
+    expect(sut).toBeInstanceOf(Logger)
+  })
+
+  it('should tell', () => {
+    Logger
+      .tell('starting Logger')
+      .flatMap(b => new Logger([`adding 3 to ${b}`], b + 3))
+      .flatMap(b => new Logger([`adding 3 to ${b}`], b + 3))
+      .runUsing(a => {
+        expect(a.logs).toEqual([
+          'starting Logger',
+          'adding 3 to 0',
+          'adding 3 to 3'
+        ])
+        expect(a.value).toEqual(6)
+      })
+  })
+
+  it('should tell', () => {
+    Logger
+      .tell('starting Logger')
+      .of('ofed')
+      .runUsing(a => {
+        expect(a.logs).toEqual([])
+        expect(a.value).toEqual('ofed')
+      })
+  })
+
+  it('should construt static', () => {
+    const sut = Logger.logger(['starting with 100'], 100)
+      .flatMap(b => new Logger(['adding 3'], b + 3))
+
+    expect(sut).toBeInstanceOf(Logger)
+  })
+
+  it('should todo...', () => {
+    Logger
+      .startWith('Starting calculation with value: 100', 100)
+      .flatMap(b => new Logger([`adding 3 to ${b}`], b + 3))
+      .runUsing(a => {
+        expect(a.logs).toEqual([
+          'Starting calculation with value: 100',
+          'adding 3 to 100'
+        ])
+        expect(a.value).toEqual(103)
+      })
+  })
+
+  it('should todo...', () => {
+    Logger
+      .startWith('Starting calculation with value: 100', 100)
+      .flatMapPair(b => [`adding 3 to ${b}`, b + 3])
+      .runUsing(a => {
+        expect(a.logs).toEqual([
+          'Starting calculation with value: 100',
+          'adding 3 to 100'
+        ])
+        expect(a.value).toEqual(103)
+      })
+  })
+
+})

src/logger/logger.ts

@@ -0,0 +1,55 @@
+import { IMonad } from '../monad/monad.interface'
+
+/**
+ * @name Logger
+ * @class Perform calculation while collecting logs 
+ */
+export class Logger<TLogs, TValue> implements IMonad<TValue>  {
+
+  /**
+   * @description Construct a Logger object.
+   * @constructor
+   * @param {TLogs[]} logs The collection of logs.
+   * @param {TValue} value The value to wrap.
+   */
+  constructor(private readonly logs: TLogs[], private readonly value: TValue) { }
+
+  /**
+   * @name Logger
+   * @description Helper function to build a Logger object.
+   * @static
+   * @param {TLogs[]} story The collection of logs.
+   * @param {TValue} value The value to wrap.
+   * @returns {Logger<TLogs, TValue>} A Logger object containing the collection of logs and value.
+   */
+  public static logger<TLogs, TValue>(logs: TLogs[], value: TValue): Logger<TLogs, TValue> {
+    return new Logger(logs, value)
+  }
+
+  public static tell<TLogs>(s: TLogs): Logger<TLogs, number> {
+    return new Logger([s], 0)
+  }
+
+  public static startWith<TLogs, TValue>(s: TLogs, value: TValue): Logger<TLogs, TValue> {
+    return new Logger([s], value)
+  }
+
+  public of<TValue>(v: TValue): Logger<TLogs, TValue> {
+    return new Logger<TLogs, TValue>([], v)
+  }
+
+  public flatMap<TValueB>(fn: (value: TValue) => Logger<TLogs, TValueB>): Logger<TLogs, TValueB> {
+    const result = fn(this.value)
+    return new Logger(this.logs.concat(result.logs), result.value)
+  }
+
+  public flatMapPair<TValueB>(fn: (value: TValue) => [TLogs, TValueB]): Logger<TLogs, TValueB> {
+    const result = fn(this.value)
+    return new Logger(this.logs.concat(result[0]), result[1])
+  }
+
+  public runUsing<TOutput>(fn: (opts: { logs: TLogs[]; value: TValue }) => TOutput): TOutput {
+    return fn({ logs: this.logs, value: this.value })
+  }
+
+}

src/logger/public_api.spec.ts

@@ -0,0 +1,7 @@
+import { Logger } from './public_api'
+
+describe('logger api', () => {
+  it('should export', () => {
+    expect(new Logger([], 'valie')).toBeInstanceOf(Logger)
+  })
+})

src/logger/public_api.ts

@@ -0,0 +1 @@
+export * from './logger'