Add repeatFn sample

4. Concurrency Patterns in Go
->Pipelines
->Some Handy Generators

concurrency-patterns-in-go/pipelines/some-handy-generators/fig-take-and-repeatfn-pipeline.go

@@ -0,0 +1,52 @@
+package main
+
+import (
+	"fmt"
+	"math/rand"
+)
+
+func main() {
+	repeatFn := func(
+		done <-chan interface{},
+		fn func() interface{},
+	) <-chan interface{} {
+		valueStream := make(chan interface{})
+		go func() {
+			defer close(valueStream)
+			for {
+				select {
+				case <-done:
+					return
+				case valueStream <- fn():
+				}
+			}
+		}()
+		return valueStream
+	}
+	take := func(
+		done <-chan interface{},
+		valueStream <-chan interface{},
+		num int,
+	) <-chan interface{} {
+		takeStream := make(chan interface{})
+		go func() {
+			defer close(takeStream)
+			for i := 0; i < num; i++ {
+				select {
+				case <-done:
+					return
+				case takeStream <- <-valueStream:
+				}
+			}
+		}()
+		return takeStream
+	}
+	done := make(chan interface{})
+	defer close(done)
+
+	rand := func() interface{} { return rand.Int() }
+
+	for num := range take(done, repeatFn(done, rand), 10) {
+		fmt.Println(num)
+	}
+}