Generator/Exponential: Difference between revisions

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@@ Line 687: / Line 687: @@
         fmt.Print(fGen(), " ")
     }
-    fmt.Println("")
+    fmt.Println()
 }</lang>
 Output:
@@ Line 693: / Line 693: @@
 576 625 676 784 841 900 961 1024 1089
 </pre>
+Alternatively, generators can be implemented in Go with goroutines and channels.  There are tradeoffs however, and often one technique is a significantly better choice.
+Goroutines can run concurrently, but there is overhead associated with thread scheduling and channel communication.  Flow control is also different.  A generator implemented as a closure is a function with a single entry point fixed at the beginning.  On repeated calls, execution always starts over at the beginning and ends when a value is returned.  A generator implemented as a goroutine, on the other hand, "returns" a value by sending it on a channel, and then the goroutine continues execution from that point.  This allows more flexibility in structuring code.
+<lang go>package main
+import (
+    "fmt"
+    "math"
+)
+func newPowGen(e float64) chan float64 {
+    ch := make(chan float64)
+    go func() {
+        for i := 0.; ; i++ {
+            ch <- math.Pow(i, e)
+        }
+    }()
+    return ch
+}
+// given two input channels, a and b, both known to return monotonically
+// increasing values, supply on channel c values of a not returned by b.
+func newMonoIncA_NotMonoIncB_Gen(a, b chan float64) chan float64 {
+    ch := make(chan float64)
+    go func() {
+        for va, vb := <-a, <-b; ; {
+            switch {
+            case va < vb:
+                ch <- va
+                fallthrough
+            case va == vb:
+                va = <-a
+            default:
+                vb = <-b
+            }
+        }
+    }()
+    return ch
+}
+func main() {
+    ch := newMonoIncA_NotMonoIncB_Gen(newPowGen(2), newPowGen(3))
+    for i := 0; i < 20; i++ {
+        <-ch
+    }
+    for i := 0; i < 10; i++ {
+        fmt.Print(<-ch, " ")
+    }
+    fmt.Println()
+}</lang>
 =={{header|Haskell}}==