add thunk type

Signed-off-by: Xe Iaso <me@christine.website>

option.go

@@ -21,13 +21,23 @@ func (o Option[T]) IsNone() bool {
 	return !o.IsSome()
 }
 
-// Take a value out of the option if it exists.
-func (o Option[T]) Take() (*T, error) {
+// Yank will pull a value out of an option, panicking if it doesn't exist.
+func (o Option[T]) Yank() T {
 	if o.IsNone() {
-		return nil, ErrOptionIsNone
+		panic("gonads: Yank on None Option")
 	}
 	
-	return o.val, nil
+	return *o.val
+}
+
+// Take a value out of the option if it exists.
+func (o Option[T]) Take() (T, error) {
+	if o.IsNone() {
+		var zero T
+		return zero, ErrOptionIsNone
+	}
+
+	return *o.val, nil
 }
 
 // Set the value of the option to a given value.

thunk.go

@@ -0,0 +1,31 @@
+package gonads
+
+// Thunk contains a partially computed value. This thunk is also lazy because
+// it will only run the underlying thunked action _once_ and then return the
+// result of that action, caching it for further use.
+//
+// If this is confusing to you, consider the following JavaScript:
+//
+//    let add = (x, y) => x + y;
+//    let addCurr = (x) => (y) => x + y;
+//    console.log(add(2, 2)); // 4
+//    console.log(addCurr(2)(2)); // 4
+//    let addTwo = addCurr(2); // (y) => 2 + y;
+//
+// In this example, `addTwo` is a thunk that contains a partially applied addCurr
+// invocation.
+type Thunk[T any] struct {
+	doer func(T) T // action being thunked
+	o    Option[T] // cache for complete thunk data
+}
+
+// Force evaluates a Thunk's action if it needs to, otherwise it returns the
+// previously evaluated result.
+func (t Thunk[T]) Force(inp T) T {
+	if t.o.IsSome() {
+		return t.o.Yank()
+	}
+
+	t.o.Set(t.doer(inp))
+	return t.o.Yank()
+}

thunk_test.go

@@ -0,0 +1,32 @@
+package gonads
+
+import (
+	"testing"
+)
+
+func Fib(n int) int {
+	if n <= 1 {
+		return n
+	}
+	return Fib(n-1) + Fib(n-2)
+}
+
+func TestRecurFib(t *testing.T) {
+	t.Log(Fib(40))
+}
+
+func TestThunkFib(t *testing.T) {
+	cache := make([]Thunk[int], 41)
+	cache[0].o.Set(0)
+	cache[1].o.Set(1)
+
+	fib := func(n int) int {
+		return cache[n-1].Force(n-1) + cache[n-2].Force(n-2)
+	}
+	
+	for i := range cache {
+		cache[i].doer = fib
+	}
+
+	t.Log(cache[40].Force(40))
+}