raise warnings when of is called on Left or Right classes

appendix_b.md

@@ -62,6 +62,10 @@ class Left extends Either {
     return false;
   }
 
+  static of(x) {
+    throw new Error('`of` called on class Left (value) instead of Either (type)');
+  }
+
   inspect() {
     return `Left(${inspect(this.$value)})`;
   }
@@ -104,6 +108,10 @@ class Right extends Either {
     return true;
   }
 
+  static of(x) {
+    throw new Error('`of` called on class Right (value) instead of Either (type)');
+  }
+
   inspect() {
     return `Right(${inspect(this.$value)})`;
   }

ch08.md

@@ -258,7 +258,7 @@ class Left extends Either {
 
 class Right extends Either {
   map(f) {
-    return Right.of(f(this.$value));
+    return Either.of(f(this.$value));
   }
 
   inspect() {
@@ -572,10 +572,10 @@ Even with `Task`, our `IO` and `Either` functors are not out of a job. Bear with
 // dbUrl :: Config -> Either Error Url
 const dbUrl = ({ uname, pass, db }) => {
   if (uname && pass && host && db) {
-    return Right.of(`db:pg://${uname}:${pass}@${host}5432/${db}`);
+    return Either.of(`db:pg://${uname}:${pass}@${host}5432/${db}`);
   }
 
-  return Left.of(Error('Invalid config!'));
+  return left(Error('Invalid config!'));
 };
 
 // connectDb :: Config -> Either Error (IO DbConnection)
@@ -666,7 +666,7 @@ We can instantly see and refactor code based on properties held by all functors.
 Functors can stack:
 
 ```js
-const nested = Task.of([Right.of('pillows'), Left.of('no sleep for you')]);
+const nested = Task.of([Either.of('pillows'), left('no sleep for you')]);
 
 map(map(map(toUpperCase)), nested);
 // Task([Right('PILLOWS'), Left('no sleep for you')])