Add new fromEither

Author: futpib

index.js

@@ -2394,14 +2394,14 @@
   //. Takes a default value and an Either, and returns the Left value
   //. if the Either is a Left; the default value otherwise.
   //.
-  //. See also [`either`](#either) and [`fromRight`](#fromRight).
+  //. See also [`fromRight`](#fromRight).
   //.
   //. ```javascript
-  //. > S.fromLeft ('abc') (S.Left ('xyz'))
-  //. 'xyz'
+  //. > S.fromLeft (0) (S.Left (42))
+  //. 42
   //.
-  //. > S.fromLeft ('abc') (S.Right (123))
-  //. 'abc'
+  //. > S.fromLeft (0) (S.Right (42))
+  //. 0
   //. ```
   function fromLeft(x) {
     return either (I) (K (x));
@@ -2417,14 +2417,14 @@
   //. Takes a default value and an Either, and returns the Right value
   //. if the Either is a Right; the default value otherwise.
   //.
-  //. See also [`either`](#either) and [`fromLeft`](#fromLeft).
+  //. See also [`fromLeft`](#fromLeft).
   //.
   //. ```javascript
-  //. > S.fromRight (123) (S.Right (789))
-  //. 789
+  //. > S.fromRight (0) (S.Right (42))
+  //. 42
   //.
-  //. > S.fromRight (123) (S.Left ('abc'))
-  //. 123
+  //. > S.fromRight (0) (S.Left (42))
+  //. 0
   //. ```
   function fromRight(x) {
     return either (K (x)) (I);
@@ -2435,28 +2435,22 @@
     impl: fromRight
   };
 
-  //# fromEither :: b -> Either a b -> b
-  //.
-  //. Takes a default value and an Either, and returns the Right value
-  //. if the Either is a Right; the default value otherwise.
+  //# fromEither :: Either a a -> a
   //.
-  //. The behaviour of `fromEither` is likely to change in a future release.
-  //. Please use [`fromRight`](#fromRight) instead.
+  //. Takes an Either with the same type on the Left and on the Right
+  //. and return whichever value exists.
   //.
   //. ```javascript
-  //. > S.fromEither (0) (S.Right (42))
+  //. > S.fromEither (S.Right (42))
   //. 42
   //.
-  //. > S.fromEither (0) (S.Left (42))
-  //. 0
+  //. > S.fromEither (S.Left (42))
+  //. 42
   //. ```
-  function fromEither(x) {
-    return either (K (x)) (I);
-  }
   _.fromEither = {
     consts: {},
-    types: [b, $.Either (a) (b), b],
-    impl: fromEither
+    types: [$.Either (a) (a), a],
+    impl: either (I) (I)
   };
 
   //# lefts :: (Filterable f, Functor f) => f (Either a b) -> f a

test/fromEither.js

@@ -7,9 +7,9 @@ const eq = require ('./internal/eq');
 
 test ('fromEither', () => {
 
-  eq (S.show (S.fromEither)) ('fromEither :: b -> Either a b -> b');
+  eq (S.show (S.fromEither)) ('fromEither :: Either a a -> a');
 
-  eq (S.fromEither (0) (S.Left (42))) (0);
-  eq (S.fromEither (0) (S.Right (42))) (42);
+  eq (S.fromEither (S.Left (42))) (42);
+  eq (S.fromEither (S.Right (42))) (42);
 
 });