go/ast: examples for ast.Print, ast.Inspect

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5700057

src/pkg/go/ast/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 ast_test
+
+import (
+	"fmt"
+	"go/ast"
+	"go/parser"
+	"go/token"
+)
+
+// This example demonstrates how to inspect the AST of a Go program.
+func ExampleInspect() {
+	// src is the input for which we want to inspect the AST.
+	src := `
+package p
+const c = 1.0
+var X = f(3.14)*2 + c
+`
+
+	// Create the AST by parsing src.
+	fset := token.NewFileSet() // positions are relative to fset
+	f, err := parser.ParseFile(fset, "src.go", src, 0)
+	if err != nil {
+		panic(err)
+	}
+
+	// Inspect the AST and print all identifiers and literals.
+	ast.Inspect(f, func(n ast.Node) bool {
+		var s string
+		switch x := n.(type) {
+		case *ast.BasicLit:
+			s = x.Value
+		case *ast.Ident:
+			s = x.Name
+		}
+		if s != "" {
+			fmt.Printf("%s:\t%s\n", fset.Position(n.Pos()), s)
+		}
+		return true
+	})
+
+	// output:
+	// src.go:2:9:	p
+	// src.go:3:7:	c
+	// src.go:3:11:	1.0
+	// src.go:4:5:	X
+	// src.go:4:9:	f
+	// src.go:4:11:	3.14
+	// src.go:4:17:	2
+	// src.go:4:21:	c
+}
+
+// This example shows what an AST looks like when printed for debugging.
+func ExamplePrint() {
+	// src is the input for which we want to print the AST.
+	src := `
+package main
+func main() {
+	println("Hello, World!")
+}
+`
+
+	// Create the AST by parsing src.
+	fset := token.NewFileSet() // positions are relative to fset
+	f, err := parser.ParseFile(fset, "", src, 0)
+	if err != nil {
+		panic(err)
+	}
+
+	// Print the AST.
+	ast.Print(fset, f)
+
+	// output:
+	//      0  *ast.File {
+	//      1  .  Package: 2:1
+	//      2  .  Name: *ast.Ident {
+	//      3  .  .  NamePos: 2:9
+	//      4  .  .  Name: "main"
+	//      5  .  }
+	//      6  .  Decls: []ast.Decl (len = 1) {
+	//      7  .  .  0: *ast.FuncDecl {
+	//      8  .  .  .  Name: *ast.Ident {
+	//      9  .  .  .  .  NamePos: 3:6
+	//     10  .  .  .  .  Name: "main"
+	//     11  .  .  .  .  Obj: *ast.Object {
+	//     12  .  .  .  .  .  Kind: func
+	//     13  .  .  .  .  .  Name: "main"
+	//     14  .  .  .  .  .  Decl: *(obj @ 7)
+	//     15  .  .  .  .  }
+	//     16  .  .  .  }
+	//     17  .  .  .  Type: *ast.FuncType {
+	//     18  .  .  .  .  Func: 3:1
+	//     19  .  .  .  .  Params: *ast.FieldList {
+	//     20  .  .  .  .  .  Opening: 3:10
+	//     21  .  .  .  .  .  Closing: 3:11
+	//     22  .  .  .  .  }
+	//     23  .  .  .  }
+	//     24  .  .  .  Body: *ast.BlockStmt {
+	//     25  .  .  .  .  Lbrace: 3:13
+	//     26  .  .  .  .  List: []ast.Stmt (len = 1) {
+	//     27  .  .  .  .  .  0: *ast.ExprStmt {
+	//     28  .  .  .  .  .  .  X: *ast.CallExpr {
+	//     29  .  .  .  .  .  .  .  Fun: *ast.Ident {
+	//     30  .  .  .  .  .  .  .  .  NamePos: 4:2
+	//     31  .  .  .  .  .  .  .  .  Name: "println"
+	//     32  .  .  .  .  .  .  .  }
+	//     33  .  .  .  .  .  .  .  Lparen: 4:9
+	//     34  .  .  .  .  .  .  .  Args: []ast.Expr (len = 1) {
+	//     35  .  .  .  .  .  .  .  .  0: *ast.BasicLit {
+	//     36  .  .  .  .  .  .  .  .  .  ValuePos: 4:10
+	//     37  .  .  .  .  .  .  .  .  .  Kind: STRING
+	//     38  .  .  .  .  .  .  .  .  .  Value: "\"Hello, World!\""
+	//     39  .  .  .  .  .  .  .  .  }
+	//     40  .  .  .  .  .  .  .  }
+	//     41  .  .  .  .  .  .  .  Ellipsis: -
+	//     42  .  .  .  .  .  .  .  Rparen: 4:25
+	//     43  .  .  .  .  .  .  }
+	//     44  .  .  .  .  .  }
+	//     45  .  .  .  .  }
+	//     46  .  .  .  .  Rbrace: 5:1
+	//     47  .  .  .  }
+	//     48  .  .  }
+	//     49  .  }
+	//     50  .  Scope: *ast.Scope {
+	//     51  .  .  Objects: map[string]*ast.Object (len = 1) {
+	//     52  .  .  .  "main": *(obj @ 11)
+	//     53  .  .  }
+	//     54  .  }
+	//     55  .  Unresolved: []*ast.Ident (len = 1) {
+	//     56  .  .  0: *(obj @ 29)
+	//     57  .  }
+	//     58  }
+}