cmd/godoc: add toys, tour button to playground

Fixes #3241.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5835043

doc/play/fib.go

+package main
+
+// fib returns a function that returns
+// successive Fibonacci numbers.
+func fib() func() int {
+	a, b := 0, 1
+	return func() int {
+		a, b = b, a+b
+		return a
+	}
+}
+
+func main() {
+	f := fib()
+	// Function calls are evaluated left-to-right.
+	println(f(), f(), f(), f(), f())
+}

doc/play/hello.go

+package main
+
+import "fmt"
+
+func main() {
+	fmt.Println("Hello, 世界")
+}

doc/play/peano.go

+// Peano integers are represented by a linked
+// list whose nodes contain no data
+// (the nodes are the data).
+// http://en.wikipedia.org/wiki/Peano_axioms
+
+// This program demonstrates the power of Go's
+// segmented stacks when doing massively
+// recursive computations.
+
+package main
+
+import "fmt"
+
+// Number is a pointer to a Number
+type Number *Number
+
+// The arithmetic value of a Number is the
+// count of the nodes comprising the list.
+// (See the count function below.)
+
+// -------------------------------------
+// Peano primitives
+
+func zero() *Number {
+	return nil
+}
+
+func isZero(x *Number) bool {
+	return x == nil
+}
+
+func add1(x *Number) *Number {
+	e := new(Number)
+	*e = x
+	return e
+}
+
+func sub1(x *Number) *Number {
+	return *x
+}
+
+func add(x, y *Number) *Number {
+	if isZero(y) {
+		return x
+	}
+	return add(add1(x), sub1(y))
+}
+
+func mul(x, y *Number) *Number {
+	if isZero(x) || isZero(y) {
+		return zero()
+	}
+	return add(mul(x, sub1(y)), x)
+}
+
+func fact(n *Number) *Number {
+	if isZero(n) {
+		return add1(zero())
+	}
+	return mul(fact(sub1(n)), n)
+}
+
+// -------------------------------------
+// Helpers to generate/count Peano integers
+
+func gen(n int) *Number {
+	if n > 0 {
+		return add1(gen(n - 1))
+	}
+	return zero()
+}
+
+func count(x *Number) int {
+	if isZero(x) {
+		return 0
+	}
+	return count(sub1(x)) + 1
+}
+
+// -------------------------------------
+// Print i! for i in [0,9]
+
+func main() {
+	for i := 0; i <= 9; i++ {
+		f := count(fact(gen(i)))
+		fmt.Println(i, "! =", f)
+	}
+}

doc/play/pi.go

+// Concurrent computation of pi.
+// See http://goo.gl/ZuTZM.
+//
+// This demonstrates Go's ability to handle
+// large numbers of concurrent processes.
+// It is an unreasonable way to calculate pi.
+package main
+
+import (
+	"fmt"
+	"math"
+)
+
+func main() {
+	fmt.Println(pi(5000))
+}
+
+// pi launches n goroutines to compute an
+// approximation of pi.
+func pi(n int) float64 {
+	ch := make(chan float64)
+	for k := 0; k <= n; k++ {
+		go term(ch, float64(k))
+	}
+	f := 0.0
+	for k := 0; k <= n; k++ {
+		f += <-ch
+	}
+	return f
+}
+
+func term(ch chan float64, k float64) {
+	ch <- 4 * math.Pow(-1, k) / (2*k + 1)
+}

doc/play/playground.js

@@ -12,6 +12,7 @@
 // 	preCompile - callback to mutate request data before compiling
 // 	postCompile - callback to read response data after compiling
 //      simple - use plain textarea instead of CodeMirror.
+//      toysEl - select element with a list of toys.
 function playground(opts) {
 	var simple = opts['simple'];
 	var code = $(opts['codeEl']);
@@ -109,6 +110,16 @@ function playground(opts) {
 		}
 		return $(opts['codeEl']).val();
 	}
+	function setBody(text) {
+		if (editor) {
+			editor.setValue(text);
+			return;
+		}
+		$(opts['codeEl']).val(text);
+	}
+	function origin(href) {
+		return (""+href).split("/").slice(0, 3).join("/");
+	}
 
 	var seq = 0;
 	function run() {
@@ -164,14 +175,7 @@ function playground(opts) {
 	}
 	$(opts['runEl']).click(run);
 
-	if (opts['shareEl'] == null || (opts['shareURLEl'] == null && opts['shareRedirect'] == null)) {
-		return editor;
-	}
-
-	function origin(href) {
-		return (""+href).split("/").slice(0, 3).join("/");
-	}
-
+	if (opts['shareEl'] != null && (opts['shareURLEl'] != null || opts['shareRedirect'] != null)) {
 		var shareURL;
 		if (opts['shareURLEl']) {
 			shareURL = $(opts['shareURLEl']).hide();
@@ -194,13 +198,30 @@ function playground(opts) {
 						window.location = opts['shareRedirect'] + xhr.responseText;
 					}
 					if (shareURL) {
-					var url = origin(window.location) + "/p/" +
-						xhr.responseText;
+						var url = origin(window.location) + "/p/" + xhr.responseText;
 						shareURL.show().val(url).focus().select();
 					}
 				}
 			});
 		});
+	}
+
+	if (opts['toysEl'] != null) {
+		$(opts['toysEl']).bind('change', function() {
+			var toy = $(this).val();
+			$.ajax("/doc/play/"+toy, {
+				processData: false,
+				type: "GET",
+				complete: function(xhr) {
+					if (xhr.status != 200) {
+						alert("Server error; try again.")
+						return;
+					}
+					setBody(xhr.responseText);
+				}
+			});
+		});
+	}
 
 	return editor;
 }

doc/play/sieve.go

+// A concurrent prime sieve
+
+package main
+
+// Send the sequence 2, 3, 4, ... to channel 'ch'.
+func Generate(ch chan<- int) {
+	for i := 2; ; i++ {
+		ch <- i // Send 'i' to channel 'ch'.
+	}
+}
+
+// Copy the values from channel 'in' to channel 'out',
+// removing those divisible by 'prime'.
+func Filter(in <-chan int, out chan<- int, prime int) {
+	for {
+		i := <-in // Receive value from 'in'.
+		if i%prime != 0 {
+			out <- i // Send 'i' to 'out'.
+		}
+	}
+}
+
+// The prime sieve: Daisy-chain Filter processes.
+func main() {
+	ch := make(chan int) // Create a new channel.
+	go Generate(ch)      // Launch Generate goroutine.
+	for i := 0; i < 10; i++ {
+		prime := <-ch
+		print(prime, "\n")
+		ch1 := make(chan int)
+		go Filter(ch, ch1, prime)
+		ch = ch1
+	}
+}

doc/play/solitaire.go

+// This program solves the (English) peg
+// solitaire board game.
+// http://en.wikipedia.org/wiki/Peg_solitaire
+
+package main
+
+import "fmt"
+
+const N = 11 + 1 // length of a row (+1 for \n)
+
+// The board must be surrounded by 2 illegal
+// fields in each direction so that move()
+// doesn't need to check the board boundaries.
+// Periods represent illegal fields,
+// ● are pegs, and ○ are holes.
+
+var board = []int(
+	`...........
+...........
+....●●●....
+....●●●....
+..●●●●●●●..
+..●●●○●●●..
+..●●●●●●●..
+....●●●....
+....●●●....
+...........
+...........
+`)
+
+// center is the position of the center hole if 
+// there is a single one; otherwise it is -1.
+var center int
+
+func init() {
+	n := 0
+	for pos, field := range board {
+		if field == '○' {
+			center = pos
+			n++
+		}
+	}
+	if n != 1 {
+		center = -1 // no single hole
+	}
+}
+
+var moves int // number of times move is called
+
+// move tests if there is a peg at position pos that 
+// can jump over another peg in direction dir. If the
+// move is valid, it is executed and move returns true.
+// Otherwise, move returns false.
+func move(pos, dir int) bool {
+	moves++
+	if board[pos] == '●' && board[pos+dir] == '●' && board[pos+2*dir] == '○' {
+		board[pos] = '○'
+		board[pos+dir] = '○'
+		board[pos+2*dir] = '●'
+		return true
+	}
+	return false
+}
+
+// unmove reverts a previously executed valid move.
+func unmove(pos, dir int) {
+	board[pos] = '●'
+	board[pos+dir] = '●'
+	board[pos+2*dir] = '○'
+}
+
+// solve tries to find a sequence of moves such that 
+// there is only one peg left at the end; if center is 
+// >= 0, that last peg must be in the center position.
+// If a solution is found, solve prints the board after
+// each move in a backward fashion (i.e., the last 
+// board position is printed first, all the way back to
+// the starting board position).
+func solve() bool {
+	var last, n int
+	for pos, field := range board {
+		// try each board position
+		if field == '●' {
+			// found a peg
+			for _, dir := range [...]int{-1, -N, +1, +N} {
+				// try each direction
+				if move(pos, dir) {
+					// a valid move was found and executed,
+					// see if this new board has a solution
+					if solve() {
+						unmove(pos, dir)
+						println(string(board))
+						return true
+					}
+					unmove(pos, dir)
+				}
+			}
+			last = pos
+			n++
+		}
+	}
+	// tried each possible move
+	if n == 1 && (center < 0 || last == center) {
+		// there's only one peg left
+		println(string(board))
+		return true
+	}
+	// no solution found for this board
+	return false
+}
+
+func main() {
+	if !solve() {
+		fmt.Println("no solution found")
+	}
+	fmt.Println(moves, "moves tried")
+}

doc/play/tree.go

+// Go's concurrency primitives make it easy to
+// express concurrent concepts, such as
+// this binary tree comparison.
+//
+// Trees may be of different shapes, 
+// but have the same contents. For example:
+//
+//        4               6
+//      2   6          4     7
+//     1 3 5 7       2   5
+//                  1 3
+//
+// This program compares a pair of trees by
+// walking each in its own goroutine,
+// sending their contents through a channel
+// to a third goroutine that compares them.
+
+package main
+
+import (
+	"fmt"
+	"math/rand"
+)
+
+// A Tree is a binary tree with integer values.
+type Tree struct {
+	Left  *Tree
+	Value int
+	Right *Tree
+}
+
+// Walk traverses a tree depth-first, 
+// sending each Value on a channel.
+func Walk(t *Tree, ch chan int) {
+	if t == nil {
+		return
+	}
+	Walk(t.Left, ch)
+	ch <- t.Value
+	Walk(t.Right, ch)
+}
+
+// Walker launches Walk in a new goroutine,
+// and returns a read-only channel of values.
+func Walker(t *Tree) <-chan int {
+	ch := make(chan int)
+	go func() {
+		Walk(t, ch)
+		close(ch)
+	}()
+	return ch
+}
+
+// Compare reads values from two Walkers
+// that run simultaneously, and returns true
+// if t1 and t2 have the same contents.
+func Compare(t1, t2 *Tree) bool {
+	c1, c2 := Walker(t1), Walker(t2)
+	for {
+		v1, ok1 := <-c1
+		v2, ok2 := <-c2
+		if !ok1 || !ok2 {
+			return ok1 == ok2
+		}
+		if v1 != v2 {
+			break
+		}
+	}
+	return false
+}
+
+// New returns a new, random binary tree
+// holding the values 1k, 2k, ..., nk.
+func New(n, k int) *Tree {
+	var t *Tree
+	for _, v := range rand.Perm(n) {
+		t = insert(t, (1+v)*k)
+	}
+	return t
+}
+
+func insert(t *Tree, v int) *Tree {
+	if t == nil {
+		return &Tree{nil, v, nil}
+	}
+	if v < t.Value {
+		t.Left = insert(t.Left, v)
+		return t
+	}
+	t.Right = insert(t.Right, v)
+	return t
+}
+
+func main() {
+	t1 := New(100, 1)
+	fmt.Println(Compare(t1, New(100, 1)), "Same Contents")
+	fmt.Println(Compare(t1, New(99, 1)), "Differing Sizes")
+	fmt.Println(Compare(t1, New(100, 2)), "Differing Values")
+	fmt.Println(Compare(t1, New(101, 2)), "Dissimilar")
+}

doc/root.html

@@ -24,8 +24,20 @@ Hello, 世界
 </pre>
 </div>
 <div class="buttons">
-<a class="run" href="#">Run</a>
-<a class="share" href="#">Share</a>
+<a class="run" href="#" title="Run this code [shift-enter]">Run</a>
+<a class="share" href="#" title="Share this code">Share</a>
+<a class="tour" href="http://tour.golang.org/" title="Learn Go from your browser">Tour</a>
+</div>
+<div class="toys">
+<select>
+	<option value="hello.go">Hello, World!</option>
+	<option value="fib.go">Fibonacci Closure</option>
+	<option value="peano.go">Peano Integers</option>
+	<option value="pi.go">Concurrent pi</option>
+	<option value="sieve.go">Concurrent Prime Sieve</option>
+	<option value="solitaire.go">Peg Solitaire Solver</option>
+	<option value="tree.go">Tree Comparison</option>
+</select>
 </div>
 </div>
 
@@ -117,7 +129,8 @@ function init() {
 		"outputEl":      "#learn .output",
 		"runEl":         "#learn .run",
 		"shareEl":       "#learn .share",
-		"shareRedirect": "http://play.golang.org/p/"
+		"shareRedirect": "http://play.golang.org/p/",
+		"toysEl":        "#learn .toys select"
 	});
 }
 

doc/style.css

@@ -322,21 +322,21 @@ div#learn .output {
 	border: 1px solid #375EAB;
 }
 div#learn .buttons {
+	float: right;
 	padding: 20px 0 10px 0;
 	text-align: right;
 }
 div#learn .buttons a {
 	height: 16px;
 	margin-left: 5px;
-
 	padding: 10px;
 }
-div#learn .buttons .tour {
-	float: right;
+div#learn .toys {
+	margin-top: 8px;
 }
-div#learn .buttons .tour a {
-	margin-right: 0;
-	font-weight: bold;
+div#learn .toys select {
+	border: 1px solid #375EAB;
+	margin: 0;
 }
 
 div#blog,

src/cmd/godoc/godoc.go

@@ -102,6 +102,7 @@ func registerPublicHandlers(mux *http.ServeMux) {
 	mux.Handle(cmdHandler.pattern, &cmdHandler)
 	mux.Handle(pkgHandler.pattern, &pkgHandler)
 	mux.HandleFunc("/doc/codewalk/", codewalk)
+	mux.Handle("/doc/play/", fileServer)
 	mux.HandleFunc("/search", search)
 	mux.Handle("/robots.txt", fileServer)
 	mux.HandleFunc("/opensearch.xml", serveSearchDesc)