Add Tag type and hasTag function

src/lib/util/basic/utility.ts

@@ -174,5 +174,11 @@ export const tryCatch = <A>(f: () => A): Either<A, Error> => {
   }
 }
 
+export interface Tag<T> {
+  readonly _tag: T
+}
+
+export const hasTag = (x: string) => (y: Tag<string>) => x === y._tag
+
 export const fromNullable = <A>(a: A | null | undefined): Option<A> =>
   a == null ? none : some(a)