feat: Add reponse types for typesafe returns

src/response.ts

@@ -0,0 +1,44 @@
+export type Response<T, E> = Valid<T, E> | Err<T, E>
+
+export const valid = <T, E>(value: T): Valid<T, E> => new Valid(value)
+export const err = <T, E>(error: E): Err<T, E> => new Err(error)
+
+export class Valid<T, E> {
+  constructor(readonly value: T) {}
+
+  public isValid(): this is Valid<T, E> {
+    return true
+  }
+
+  public isError(): this is Err<T, E> {
+    return !this.isValid()
+  }
+
+  public getValue(): T {
+    return this.value
+  }
+
+  public getError(): E {
+    throw new Error('Tried to get error from a success.')
+  }
+}
+
+export class Err<T, E> {
+  constructor(readonly error: E) {}
+
+  public isError(): this is Err<T, E> {
+    return true
+  }
+
+  public isValid(): this is Valid<T, E> {
+    return !this.isError()
+  }
+
+  public getValue(): T {
+    throw new Error('Tried to get success value from an error.')
+  }
+
+  public getError(): E {
+    return this.error
+  }
+}