todo.md

Core

• add tests (property-based tests for monad laws?)
• change then method to flatMap
• support async
• catch method
• correct type restrictions on errors
• sequence and parallel functions
• race function
• finally method
• catchAll method for unsoundly throw errors

Async, Concurrency & Fault Tolerance

• wait function e.g. .andThen(IO.wait(5, "seconds"))
• timeout method (implement in terms of IO.race?)
• retry method
• exponential backoff for retry
• filter for retry

Cancellation & Fibers

• Add Canceled to IOOutcome
• Add cancellation behaviour to run loop
• Add a way to interoperate with other cancellation mechanisms e.g. clearTimeout
• Support async cancel callbacks for IO.cancelable
• Fiber.start function
• Fiber.cancel method
• Fiber.outcome method
• Rewrite parallel using fibers
• Rewrite race using fibers
• IO.cancel function for a fiber to self-cancel
• IO.onCancel method for resource cleanup
• Add IO.bracket function for resource cleanup
• Add a way to create uncancelable sections

Data Structures

• Ref
• Tests for Ref
• Deferred?
• Queue?
• Batcher?
• FiberPool - for limiting concurrency. Build on top of Queue?

Performance & Internals

• make recursive IO stack-safe
• optimise to avoid creation of unnecessary promises
• write some useful benchmarks - compare async/await/throw implementation to IO
• Re-use the Wrap, Raise and Cancel class as the cases of IOResult to avoid allocations?

Code Organisation

• work out how to split into several modules
• replace IOInterface and methods object with abstract base class
• Use consistent terminology throughout - e.g. IO vs action vs effect
• Rename IOResult to Outcome or IOOutcome and IOOutcome to OutcomeKind
• Refactor IO implementation to take executeOn as a private member rather than using inheritance.
• Make type errors easier to understand by removing the massive union type.
• Remove duplication between implementations of IO.race and IO.parallel.

Ergonomics Improvements

• lift function to return IO
• map method
• mapError method
• forEach method (and parallel equivalent)
• .as method
• repeatForever method
• some more helper methods for composing independent IOs and returning the first or second value
• overload andThen to take an IO instead of a () => IO
• Support for partial functions in catch and andThen?

Documentation and Release

• Set up documentation generator.
• Publish docs to GitHub pages.
• Add "Getting Started" guide to the readme.
• Ensure all important methods and functions have doc comments.
• Publish to NPM.