diff --git a/src/lib/util/basic/either.ts b/src/lib/util/basic/either.ts
index d3f050c..92cc051 100644
--- a/src/lib/util/basic/either.ts
+++ b/src/lib/util/basic/either.ts
@@ -3,26 +3,26 @@ export type Right<A> = {readonly _tag: 'Right', readonly right: A}
 export type Either<A, E> = Right<A> | Left<E>
 
 // Constructors
-export const left = <E>(e: E): Either<E, never> => ({
+export const left = <E>(e: E): Either<never, E> => ({
   _tag: 'Left',
   left: e,
 })
-export const right = <A>(a: A): Either<never, A> => ({
+export const right = <A>(a: A): Either<A, never> => ({
   _tag: 'Right',
   right: a,
 })
 
 // Operations
 export const eitherMap =
-  <E, A, B>(f: (a: A) => B) => (fa: Either<E, A>): Either<E, B> =>
+  <E, A, B>(f: (a: A) => B) => (fa: Either<A, E>): Either<B, E> =>
     fa._tag === 'Right' ? right(f(fa.right)) : fa
 
 export const eitherChain =
-  <E, A, B>(f: (a: A) => Either<E, B>) =>
-  (fa: Either<E, A>): Either<E, B> =>
+  <E, A, B>(f: (a: A) => Either<B, E>) =>
+  (fa: Either<A, E>): Either<B, E> =>
     fa._tag === 'Right' ? f(fa.right) : fa
 
 export const fold =
-  <E, A, B>(onLeft: (e: E) => B, onRight: (a: A) => B) =>
-  (fa: Either<E, A>): B =>
+  <A, B, E>(onLeft: (e: E) => B, onRight: (a: A) => B) =>
+  (fa: Either<A, E>): B =>
     fa._tag === 'Left' ? onLeft(fa.left) : onRight(fa.right)