What is fp-go?

A comprehensive functional programming library for Go — strongly influenced by fp-ts, built around small, pure, composable functions.

// Approach

Many small, pure functions with no hidden side effects.

// Side effects

Isolated into lazy IO-style computations.

// Composition

A consistent set of combinators across every data type.

Quick example.

Difficulty · Beginner

Handle errors functionally with Either. Map transforms the success branch; errors flow through untouched.

example.gotested

import (
  "errors"
  "github.com/IBM/fp-go/either"
  "github.com/IBM/fp-go/function"
)

// Pure function that can fail
func divide(a, b int) either.Either[error, int] {
  if b == 0 {
      return either.Left[int](errors.New("division by zero"))
  }
  return either.Right[error](a / b)
}

// Compose operations safely
result := function.Pipe2(
  divide(10, 2),
  either.Map(func(x int) int { return x * 2 }),
  either.GetOrElse(func() int { return 0 }),
)
// result = 10

What this demonstrates.

Express operations that can fail using the Either type
Chain operations together safely
Handle errors explicitly without nested if statements
Write pure, composable functions