Merge pull request #86 from swan-io/from-predicate

Add Option.fromPredicate

docs/docs/option.md

@@ -264,6 +264,76 @@ option.tapSome(console.log).map((x) => x * 2);
 
 ## Statics
 
+### Option.fromNullable(value)
+
+```ts
+fromNullable(nullable: A | null | undefined): Option<A>
+```
+
+Creates an option from a nullable value, excluding `null` & `undefined`
+
+```ts title="Examples"
+Option.fromNullable(null);
+// Option.None()
+
+Option.fromNullable(undefined);
+// Option.None()
+
+Option.fromNullable(1);
+// Option.Some(1)
+```
+
+### Option.fromNull(value)
+
+```ts
+fromNull(nullable: A | null): Option<A>
+```
+
+Creates an option from a nullable value, excluding `null`
+
+```ts title="Examples"
+Option.fromNull(null);
+// Option.None()
+
+Option.fromNull(undefined);
+// Option.Some(undefined)
+
+Option.fromNull(1);
+// Option.Some(1)
+```
+
+### Option.fromUndefined(value)
+
+```ts
+fromUndefined(nullable: A | undefined): Option<A>
+```
+
+Creates an option from a nullable value, excluding `undefined`
+
+```ts title="Examples"
+Option.fromUndefined(null);
+// Option.Some(null)
+
+Option.fromUndefined(undefined);
+// Option.None()
+
+Option.fromUndefined(1);
+// Option.Some(1)
+```
+
+### Option.fromPredicate(value, predicate)
+
+```ts
+fromPredicate(value: A, f: (value: A) => boolean): Option<A>
+```
+
+Creates an option from a value and a predicate. Will return `Some(value)` if predicate returns `true`, `None` if `false`
+
+```ts title="Examples"
+Option.fromPredicate(value, (value) => value % 2 === 0);
+// Option<number> where `number` is even
+```
+
 ### Option.isOption(value)
 
 ```ts

docs/docs/result.md

@@ -319,6 +319,23 @@ result.tapError(console.log).map((x) => x * 2);
 
 ## Statics
 
+### Result.fromPredicate(value, predicate, error)
+
+```ts
+fromPredicate(value: A, f: (value: A) => boolean, errorIfFalse: E): Result<A, E>
+```
+
+Creates an option from a value and a predicate. Will return `Ok(value)` if predicate returns `true`, `Error(errorIfFalse)` if `false`
+
+```ts title="Examples"
+Result.fromPredicate(
+  value,
+  (value) => value % 2 === 0,
+  new Error("Odd number"),
+);
+// Ok<number> if `number` is even, Error<Error> if odd
+```
+
 ### Result.isResult(value)
 
 ```ts

src/OptionResult.ts

@@ -57,6 +57,29 @@ class __Option<A> {
       : Option.Some<A>(nullable);
   };
 
+  /**
+   * Create an Option from a value & predicate
+   */
+
+  static fromPredicate<A, B extends A>(
+    value: A,
+    predicate: (value: A) => value is B,
+  ): Option<B>;
+  static fromPredicate<A>(
+    value: A,
+    predicate: (value: A) => boolean,
+  ): Option<A>;
+  static fromPredicate<A>(
+    value: A,
+    predicate: (value: A) => boolean,
+  ): Option<A> {
+    if (predicate(value)) {
+      return Option.Some(value);
+    } else {
+      return NONE as Option<A>;
+    }
+  }
+
   /**
    * Turns an array of options into an option of array
    */

test/Option.test.ts

@@ -81,6 +81,11 @@ test("Option.fromUndefined", () => {
   expect(Option.fromUndefined(undefined)).toEqual(Option.None());
 });
 
+test("Option.fromPredicate", () => {
+  expect(Option.fromPredicate(1, (x) => x === 1)).toEqual(Option.Some(1));
+  expect(Option.fromPredicate(1, (x) => x === 2)).toEqual(Option.None());
+});
+
 test("Option.equals", () => {
   expect(Option.equals(Option.None(), Option.None(), (a, b) => a === b)).toBe(
     true,