Functional Programming in Go

A general purpose library offering functional tooling for Golang.

What do you mean?

isEven := func(a int) bool { return a%2 == 0 }
evens := iter.Take[int[(iter.Filter[int](iter.Count(), isEven), 3)
assert.SliceEqual(t, iter.Collect[int](evens), []int{0, 2, 4})

Not intended for production use (yet?)

This library was written to demonstrate what is possible using generics in the realm of functional programming in Go.

I've yet to formalise many things about the rules and types offered by this library.

The Iterator

The core idea of this library is the Iterator. It's an interface that describes type associated with a single receiver: Next() option.Option[T]. Simply put, calling Next() will yield the next value from an iterator. This library implements a fair number of common Iterators such as Map, Filter, Count and more described in the documentation below.

To use an example to demonstrate how Iterators can be powerfully combined, here's how you'd use a Filter and an infinite Counter to generate every possible prime number:

primes := iter.Filter[int](iter.Count(), isPrime)

Options and Results

Two core types were implemented for this package: Option[T] and Result[T].

Options represent the presence or absence of a value and come in two flavours: Some(value) and None. Iterators yield Some variants until they are exhuasted and then they yield None variants. For example, an iterator yielding the first three naturals numbers would yield Some(1), Some(2), Some(3) and None on subsequent calls to Next().

Results represent success or failure and are likewise represented by two variants: Ok(value) and Err(error).

To Do

• Write a better README
• Learn how to use go doc and generate docs
• Write some Example specs for auto-docs
• Formalise iterator rules for things like repeated calls and chain-call rules