Functional Programming in Go

A general purpose library offering functional helpers for Golang.

// Find the first 5 prime numbers
primes := iter.Take[int](iter.Filter[int](iter.Count(), isPrime), 5)
assert.SliceEqual(t, iter.Collect[int](primes), []int{2, 3, 5, 7, 11})

Read the docs.

Core concepts

This library introduces two core concepts, the Iterator and the Option. Using these two concepts this library derives many pre-defined iterators for use.

The Option

The Option is simply a type that represents the presence or absence of a value. Options behave somewhat like enumerations with two variants: Some(value) and None.

The Iterator

type Iterator[T any] interface {
	Next() option.Option[T]
}

The Iterator is an interface that defines the behaviour of some type that "yields" values. Each call to Next() on an Iterator will yield another value as defined by that specific Iterator. For example, the iterator iter.Count() yields 0, 1, 2, 3, etc. and onwards to infinity (or the integer limit!).

Iterators will yield Some(value) for as long as they have values to yield. Iterators that have exhausted all their values will then always yield None.

This library defines many iterators and a few are demonstrated below. For the entire set simply visit the package documentation.

Iterator showcase

Here are a few trivial example of what's possible using the iterators in this library.

// All even natural numbers (2, 4, 6, 8...)
isEven := func(n int) bool { return n%2 == 0 }
evens := iter.Filter[int](iter.Drop[int](iter.Count(), 1), isEven)

// All non-empty lines from a file
lines := iter.Exclude[string](iter.LinesString(file), filters.IsZero[string])

// String representations of numbers
numbers := iter.Map[int, string](iter.Count(), strconv.Itoa)