Go-fun

Utilities and immutable collections for functional programming in Golang.

For documentation, check the Go Package Documentation.

Features

• Immutable data structures
  • List (package list)
    • Slice based (package list)
    • Singly linked list (package linked)
  • Dict (package dict)
    • HashDict (package dict/hashdict)
    • ArrayDict (package dict/arraydict)
  • Set (package set)
    • HashSet (package dict/hashset)
  • Optional (package opt)
• Iterable abstraction (package iterable)
• Reducers for transforming data (map, filter, group by, etc) (package reducer)
• Equality type class (package equality)
• Hash type class (package hash)
• Generic Zero Value (package zero)
• Generic Slice functions (package slice)
• Mutable data structures (package mutable)
  • Stack

Why immutable collections?

• Immutable data is thread-safe by default
• Immutable data structures are more efficient than copying data to prevent unwanted modification
• Use immutable data structures at API boundaries to make it clear that data cannot be modified.
• Updated versions of a data structure share underlying state, which makes them more memory efficient when keeping multiple versions (in recursive algorithms, in search algorithms, for undo/history functionality)

Examples

Immutable Dict

d0 := hashdict.New[string, int](hash.String())

d1 := d0.Set("a", 1)
d2 := d1.Set("b", 42)
d3 := d2.Set("a", 7)

require.Equal(t, 1, d1.GetOrZero("a"))
require.Equal(t, 1, d2.GetOrZero("a"))
require.Equal(t, 7, d3.GetOrZero("a"))

require.Equal(t, 0, d1.GetOrZero("b"))
require.Equal(t, 42, d2.GetOrZero("b"))
require.Equal(t, 42, d3.GetOrZero("b"))

Immutable Set

Reducers

Take a slice of books and return a map where the keys are authors and the values contain all the titles of the books the author has written in or after the year 2000.

type Book struct {
	Author string
	Title  string
	Year   int
}

func TestBook(t *testing.T) {
	books := []Book{
		{"A", "Q", 1990},
		{"B", "R", 2005},
		{"A", "S", 2001},
		{"B", "T", 1999},
		{"B", "U", 2021},
	}

	m := reducer.ApplySlice(books,
		reducer.Filter(func(b Book) bool { return b.Year >= 2000 },
			reducer.GroupBy(func(b Book) string { return b.Author },
				reducer.Map(func(b Book) string { return b.Title }, reducer.ToSlice[string]()))))

	require.Equal(t, map[string][]string{
		"A": {"S"},
		"B": {"R", "U"},
	}, m)
}