go/scanner: replace comment with example

R=r
CC=golang-dev
https://golang.org/cl/5676074

src/pkg/go/scanner/example_test.go

+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package scanner_test
+
+import (
+	"fmt"
+	"go/scanner"
+	"go/token"
+)
+
+func ExampleScanner_Scan() {
+	// src is the input that we want to tokenize.
+	src := []byte("cos(x) + 1i*sin(x) // Euler")
+
+	// Initialize the scanner.
+	var s scanner.Scanner
+	fset := token.NewFileSet()                      // positions are relative to fset
+	file := fset.AddFile("", fset.Base(), len(src)) // register input "file"
+	s.Init(file, src, /* no error handler: */ nil, scanner.ScanComments)
+
+	// Repeated calls to Scan yield the token sequence found in the input.
+	for {
+		pos, tok, lit := s.Scan()
+		if tok == token.EOF {
+			break
+		}
+		fmt.Printf("%s\t%s\t%q\n", fset.Position(pos), tok, lit)
+	}
+
+	// output:
+	// 1:1	IDENT	"cos"
+	// 1:4	(	""
+	// 1:5	IDENT	"x"
+	// 1:6	)	""
+	// 1:8	+	""
+	// 1:10	IMAG	"1i"
+	// 1:12	*	""
+	// 1:13	IDENT	"sin"
+	// 1:16	(	""
+	// 1:17	IDENT	"x"
+	// 1:18	)	""
+	// 1:20	;	"\n"
+	// 1:20	COMMENT	"// Euler"
+}

src/pkg/go/scanner/scanner.go

@@ -2,21 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package scanner implements a scanner for Go source text. Takes a []byte as
-// source which can then be tokenized through repeated calls to the Scan
-// function. Typical use:
-//
-//	var s scanner.Scanner
-//	fset := token.NewFileSet()  // position information is relative to fset
-//	file := fset.AddFile(filename, fset.Base(), len(src))  // register file
-//	s.Init(file, src, nil /* no error handler */, 0)
-//	for {
-//		pos, tok, lit := s.Scan()
-//		if tok == token.EOF {
-//			break
-//		}
-//		// do something here with pos, tok, and lit
-//	}
+// Package scanner implements a scanner for Go source text.
+// It takes a []byte as source which can then be tokenized
+// through repeated calls to the Scan method.
 //
 package scanner