From 2543ac8b11af11f034836591046cdb52911f9403 Mon Sep 17 00:00:00 2001
From: Elizabeth Alexander Hunt <me@liz.coffee>
Date: Tue, 13 May 2025 09:50:15 -0700
Subject: snapshot

---
 utils/either.ts | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

(limited to 'utils/either.ts')

diff --git a/utils/either.ts b/utils/either.ts
index d21c796..10e4f43 100644
--- a/utils/either.ts
+++ b/utils/either.ts
@@ -5,14 +5,37 @@ export interface IEither<E, T> {
     errBranch: (e: E) => Ee,
     okBranch: (o: T) => Tt,
   ) => IEither<Ee, Tt>;
+  mapRight: <Tt>(mapper: (t: T) => Tt) => Either<E, Tt>;
+  mapLeft: <Ee>(mapper: (e: E) => Ee) => Either<Ee, T>;
+  flatMap: <Ee extends E, Tt>(
+    mapper: (e: T) => Either<Ee, Tt>,
+  ) => Either<Ee, Tt>;
 }
 
 export class Either<E, T> implements IEither<E, T> {
   private constructor(readonly err?: E, readonly ok?: T) {}
 
-  public mapBoth<Ee, Tt>(errBranch: (e: E) => Ee, okBranch: (t: T) => Tt) {
-    if (this.err) return new Either<Ee, Tt>(errBranch(this.err));
-    return new Either<Ee, Tt>(undefined, okBranch(this.ok!));
+  public mapBoth<Ee, Tt>(
+    errBranch: (e: E) => Ee,
+    okBranch: (t: T) => Tt,
+  ): Either<Ee, Tt> {
+    if (this.err) return Either.left(errBranch(this.err));
+    return Either.right(okBranch(this.ok!));
+  }
+
+  public flatMap<Ee extends E, Tt>(mapper: (t: T) => Either<Ee, Tt>) {
+    if (this.ok) return mapper(this.ok);
+    return this;
+  }
+
+  public mapRight<Tt>(mapper: (t: T) => Tt): Either<E, Tt> {
+    if (this.ok) return Either.right(mapper(this.ok));
+    return Either.left(this.err!);
+  }
+
+  public mapLeft<Ee>(mapper: (e: E) => Ee): Either<Ee, T> {
+    if (this.err) return Either.left(mapper(this.err));
+    return Either.right(this.ok!);
   }
 
   static left<E, T>(e: E) {
-- 
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