Generator/Exponential: Difference between revisions

Content added Content deleted

Inline

@@ Line 54: / Line 54: @@
 println()</lang>
 =={{header|Go}}==
+Generators can be implemented directly in Go by a channel fed by a goroutine.
-Go channels and goroutines implement generators directly.
+Thus a "function returning a generator" corresponds to a function that creates a channel, starts a goroutine that will send values on the channel, and returns the channel.  The function powCh does this, starting a function literal as the goroutine.  The returned channel corresponds to a generator.
+The "generator that filters..." is implemented without an extra function, simply by creating the channel and starting a (previously declared) function as a goroutine.  Here too, the created channel, chF, corresponds to a generator, once the goroutine has be started for it.
 <lang go>package main
-import "fmt"
+import (
+    "fmt"
+    "math"
+)
+// note: exponent not limited to ints
-func genSquares(ch chan<- int) {
+func powCh(e float64) <-chan float64 {
-    for i := 0; ; i++ {
-        ch <- i * i
+    ch := make(chan float64)
-    }
+    go func() {
+        // generate powers of non-negative integers
+        for i := float64(0); ; i++ {
+            ch <- math.Pow(i, e)
+        }
+    }()
+    return ch
 }
-func genCubes(ch chan<- int) {
+func genMonotonicIncA_NotMonotonicIncB(outCh chan<- float64,
+aCh, bCh <-chan float64) {
-    for i := 0; ; i++ {
-        ch <- i * i * i
-    }
-}
-// this long function name to indicate that the filtering
-// logic works only because squares and cubes are both
-// monotonically increasing over the (presumed) domain
-// of non-negative integers.
-func genMonotonicIncA_NotMonotonicIncB(outCh chan<- int, aCh, bCh <-chan int) {
     for a, b := <-aCh, <-bCh; ; {
         if a > b {
@@ Line 88: / Line 92: @@
 func main() {
+    // square and cube generators
-    chSq := make(chan int)
-    go genSquares(chSq)
+    chSq := powCh(2)
-    chCu := make(chan int)
+    chCu := powCh(3)
-    go genCubes(chCu)
+    // filtered generator (in two lines)
-    chF := make(chan int)
+    chF := make(chan float64)
     go genMonotonicIncA_NotMonotonicIncB(chF, chSq, chCu)
     for i := 0; i < 20; i++ {
         <-chF
@@ Line 101: / Line 107: @@
     }
     fmt.Println("")
+}
-}</lang>
+</lang>
 Output:
 <pre>