Merge pull request #1 from repeale/feat/option-implementation

feat: Option implementation

Author: repeale

README.md

@@ -31,6 +31,8 @@ Fp-go is a collection of Functional Programming helpers powered by Golang [1.18]
   - [Compose](#compose)
   - [Pipe](#pipe)
   - [Curry](#curry)
+- [Structs](#structs)
+  - [Option](#option)
 
 ## Install
 
@@ -232,3 +234,12 @@ Variations `Curry2`, `Curry3` and `Curry4` stating the number of params will be
 curryedSum := Curry2(func(a int, b int) int { return a + b })
 curryedSum(1)(2)
 ```
+
+## Structs
+
+#### Option
+
+Option represents encapsulation of an optional value, it might be used as the return type of functions which may or may not return a meaningful value when they are applied.
+You could instanciate an `opt.Option[T]` with a value with `opt.Some(val)`. If the value is missing you can use `opt.None[T]()`.
+
+Option exports `Some`, `None`, `IsSome`, `IsNone`, `GetOrElse`, `Match`, `Map`, `Chain`.

function.go

@@ -0,0 +1,7 @@
+package fp
+
+// Callback function that returns a specific value type
+type Lazy[T any] func() T
+
+// Callback function that takes an argument and return a value of the same type
+type LazyVal[T any] func(x T) T

option/option.go

@@ -0,0 +1,79 @@
+package opt
+
+import (
+	"github.com/repeale/fp-go"
+)
+
+// Base option struct
+type Option[T any] struct {
+	value    T
+	hasValue bool
+}
+
+// Constructor for Option with a value
+func Some[T any](value T) Option[T] {
+	return Option[T]{value, true}
+}
+
+// Constructor for Option without a value
+func None[T any]() Option[T] {
+	return Option[T]{}
+}
+
+// Helper to check if the Option has a value
+func IsSome[T any](option Option[T]) bool {
+	return option.hasValue
+}
+
+// Helper to check if the Option is missing the value
+func IsNone[T any](option Option[T]) bool {
+	return !option.hasValue
+}
+
+// Extracts the value out of the Option, if it exists. Otherwise returns the function with a default value
+func GetOrElse[T any](onNone fp.Lazy[T]) func(Option[T]) T {
+	return func(option Option[T]) T {
+
+		if IsNone(option) {
+			return onNone()
+		}
+
+		return option.value
+	}
+}
+
+// Extracts the value out of the Option, if it exists, with a function. Otherwise returns the function with a default value
+func Match[T any](onNone fp.Lazy[T], onSome fp.LazyVal[T]) func(Option[T]) T {
+	return func(option Option[T]) T {
+
+		if IsNone(option) {
+			return onNone()
+		}
+
+		return onSome(option.value)
+	}
+}
+
+// Execute the function on the Option value if it exists. Otherwise return the empty Option itself
+func Map[T any](fn fp.LazyVal[T]) func(o Option[T]) Option[T] {
+	return func(option Option[T]) Option[T] {
+
+		if IsNone(option) {
+			return None[T]()
+		}
+
+		return Some(fn(option.value))
+	}
+}
+
+// Execute a function that returns an Option on the Option value if it exists. Otherwise return the empty Option itself
+func Chain[A any, B any](fn func(a A) Option[B]) func(Option[A]) Option[B] {
+	return func(a Option[A]) Option[B] {
+
+		if IsNone(a) {
+			return None[B]()
+		}
+
+		return fn(a.value)
+	}
+}

option/option_test.go

@@ -0,0 +1,100 @@
+package opt
+
+import (
+	"testing"
+)
+
+func TestSome(t *testing.T) {
+	res := Some("val")
+	if res.hasValue != true {
+		t.Error("Some should return a struct with hasValue set to true. Received:", res.hasValue)
+	}
+}
+
+func TestNone(t *testing.T) {
+	res := None[string]()
+	if res.hasValue != false {
+		t.Error("None should return a struct with hasValue set to false. Received:", res.hasValue)
+	}
+}
+
+func TestIsSome_Some(t *testing.T) {
+	res := IsSome(Some("value"))
+	if res != true {
+		t.Error("IsSome should return true. Received:", res)
+	}
+}
+func TestIsSome_None(t *testing.T) {
+	res := IsSome(None[string]())
+	if res != false {
+		t.Error("IsSome should return false. Received:", res)
+	}
+}
+
+func TestIsNone_Some(t *testing.T) {
+	res := IsNone(None[string]())
+	if res != true {
+		t.Error("IsNone should return true. Received:", res)
+	}
+}
+func TestIsNone_None(t *testing.T) {
+	res := IsNone(Some("value"))
+	if res != false {
+		t.Error("IsNone should return false. Received:", res)
+	}
+}
+
+func TestGetOrElse_Some(t *testing.T) {
+	res := GetOrElse(func() string { return "fail" })(Some("val"))
+	if res != "val" {
+		t.Error("GetOrElse should return the Some value. Received:", res)
+	}
+}
+
+func TestGetOrElse_None(t *testing.T) {
+	res := GetOrElse(func() string { return "elseValue" })(None[string]())
+	if res != "elseValue" {
+		t.Error("GetOrElse should return the onNone() value. Received:", res)
+	}
+}
+
+func TestMatch_onSome(t *testing.T) {
+	res := Match(func() string { return "onNone" }, func(x string) string { return x + x })(Some("val"))
+	if res != "valval" {
+		t.Error("Match should return the onSome() value. Received:", res)
+	}
+}
+
+func TestMatch_onNone(t *testing.T) {
+	res := Match(func() string { return "onNone" }, func(x string) string { return x + x })(None[string]())
+	if res != "onNone" {
+		t.Error("Match should return the onNone() return value. Received:", res)
+	}
+}
+
+func TestMap_Some(t *testing.T) {
+	res := Map(func(x string) string { return x + x })(Some("val"))
+	if res.value != "valval" {
+		t.Error("Map should return the result of the callback function. Received:", res.value)
+	}
+}
+
+func TestMap_None(t *testing.T) {
+	res := Map(func(x string) string { return x + x })(None[string]())
+	if res.hasValue != false {
+		t.Error("Map should return a None value. Received:", res.value)
+	}
+}
+
+func TestChain_Some(t *testing.T) {
+	res := Chain(func(x string) Option[string] { return Some(x + x) })(Some("val"))
+	if res.hasValue != true {
+		t.Error("Chain should return a Some of string. Received:", res.value)
+	}
+}
+func TestChain_None(t *testing.T) {
+	res := Chain(func(x string) Option[string] { return Some(x + x) })(None[string]())
+	if res.hasValue != false {
+		t.Error("Chain should return a None value. Received:", res.value)
+	}
+}