fp-ts Option and Either

Convert nullables to Option and propagate typed errors with fp-ts Either.

11|3|Updated Jan 30, 2026

Search Tags:#TypeScript #monads #error-handling #analyze #Option #fp-ts #Either

Ready to run

npx skills add https://github.com/whatiskadudoing/fp-ts-skills --skill fp-ts-option-and-either

💬 Prompt for ChatGPT / Claude Chat▼

Please help me install this Agent Skill.
Skill: fp-ts Option and Either
Source: https://github.com/whatiskadudoing/fp-ts-skills/tree/main/skills/fp-option-either
Command: npx skills add https://github.com/whatiskadudoing/fp-ts-skills --skill fp-ts-option-and-either

SYSTEM DOCUMENTATION & REQUIREMENTS

What problem does it solve?

This Skill provides safe handling of nullable values and errors in TypeScript by leveraging fp-ts Option and Either, reducing runtime issues and improving type safety.

Core Features & Use Cases

Option-based handling for nullable values, reducing undefined checks.
Either-based error propagation with typed failures, enabling robust validation flows.
Seamless composition with pipe and functional utilities to build readable pipelines.
Use case: convert a nullable user id to an Option and then validate it with typed errors.

Quick Start

Install fp-ts and import the modules. Convert a nullable value to an Option using fromNullable and extract with getOrElse. Create and transform Either values with right/left and map/chain as needed.

Frequently Asked Questions about fp-ts Option and Either

High-intent search queries and answers about installing and using this skill.

FAQPage Schema

How do I handle nullable values safely in TypeScript using fp-ts?▼

To handle nullable values safely in TypeScript, convert them to Option using fp-ts fromNullable. This wraps undefined values in a typed structure, allowing you to extract them safely using getOrElse and avoid runtime errors.

What is the best way to propagate typed errors in TypeScript validation flows?▼

The best way to propagate typed errors in TypeScript is by using fp-ts Either. By returning right for success and left for failure, you can build robust validation flows that force explicit error handling at compile time.

How do I compose functional pipelines for error handling in TypeScript?▼

To compose functional pipelines for error handling in TypeScript, use fp-ts pipe with map and chain. This allows you to sequence operations that might fail, passing Either or Option values through readable transformations.

Does fp-ts Option work with fromPredicate for input validation?▼

Yes, fp-ts Option works with fromPredicate for input validation. You can use fromPredicate to check if a value meets specific criteria, automatically wrapping valid inputs in an Option and returning none if the condition fails.

When should I use fold with fp-ts Either and Option?▼

You should use fold with fp-ts Either and Option when you need to extract a final value from a pipeline. Fold forces you to handle both the success and failure cases, ensuring safe unwrapping of the monadic value.