feat: Added tryCatch() function

README.md

@@ -143,7 +143,7 @@ withDefault(left(new Error('Wrong!')), 0); // 0
 
 ### caseOf
 
-`<A, B>(caseof: {Right: (v: A) => B; Left: (v: Error) => any;}, value: Either<A>): Promise<B>`
+`caseOf<A, B>(caseof: {Right: (v: A) => B; Left: (v: Error) => any;}, value: Either<A>): Promise<B>`
 
 Run different computations depending on whether an `Either` is `Right` or `Left` and returns a `Promise`
 
@@ -159,7 +159,7 @@ caseOf(
 
 ### map
 
-`<A, B>(f: (a: A) => B, value: Either<A>): Either<B>`
+`map<A, B>(f: (a: A) => B, value: Either<A>): Either<B>`
 
 Transforms an `Either` value with a given function.
 
@@ -169,6 +169,19 @@ map(add1, right(4)); // Right<number>(5)
 map(add1, left(new Error('Something bad happened'))); // Left('Something bad happened')
 ```
 
+### tryCatch
+
+`tryCatch<A>(f: () => A, onError: (e: Error) => Error): Either<A>`
+
+Transforms a function (that might throw an exception) that produces `A` to a function that produces `Either<A>`.
+
+```ts
+tryCatch(
+  () => JSON.parse(''),
+  err => err
+); // Left('Unexpected end of JSON input')
+```
+
 ### andThen
 
 `andThen<A, B>(f: (a: A) => Either<B>, value: Either<A>): Either<B>`

package.json

@@ -1,6 +1,6 @@
 {
   "name": "ts.data.either",
-  "version": "1.0.0",
+  "version": "2.1.0",
   "description": "A Typescript implementation of the Either data type",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",

src/either.spec.ts

@@ -7,7 +7,8 @@ import {
   map,
   andThen,
   Either,
-  caseOf
+  caseOf,
+  tryCatch
 } from './either';
 
 import * as chai from 'chai';
@@ -163,6 +164,32 @@ describe('Either', () => {
     });
   });
 
+  describe('tryCatch', () => {
+    let shouldFail: boolean;
+    const fn = () => {
+      if (shouldFail) {
+        throw anError();
+      }
+      return 'Ok';
+    };
+    it('should convert a failing function into a Left', () => {
+      shouldFail = true;
+      return expect(
+        caseOf(
+          {
+            Left: err => `Error: ${err.message}`,
+            Right: n => `Launch ${n} missiles`
+          },
+          tryCatch(fn, err => err)
+        )
+      ).to.be.rejectedWith('Error: Something is wrong');
+    });
+    it('should convert a successful function into a Right', () => {
+      shouldFail = false;
+      expect(tryCatch(fn, err => err)).to.deep.equal(right('Ok'));
+    });
+  });
+
   describe('examples', () => {
     type Band = {
       artist: string;
@@ -237,5 +264,21 @@ describe('Either', () => {
         )
       ).to.be.rejectedWith(`Unexpected end of JSON input`);
     });
+
+    it('should be a good tryCatch example', () => {
+      const res = tryCatch(
+        () => JSON.parse(''),
+        err => err
+      );
+      return expect(
+        caseOf(
+          {
+            Left: err => err.message,
+            Right: result => result
+          },
+          res
+        )
+      ).to.be.rejectedWith(`Unexpected end of JSON input`);
+    });
   });
 });

src/either.ts

@@ -73,3 +73,14 @@ export const caseOf = <A, B>(
       return Promise.resolve(caseof.Right((value as Right<A>)._value));
   }
 };
+
+export const tryCatch = <A>(
+  f: () => A,
+  onError: (e: Error) => Error
+): Either<A> => {
+  try {
+    return right(f());
+  } catch (e) {
+    return left(onError(e));
+  }
+};

src/index.ts

@@ -7,5 +7,6 @@ export {
   withDefault,
   map,
   andThen,
-  caseOf
+  caseOf,
+  tryCatch
 } from './either';