Golang go/ast.Fprint() function example

package go/ast

Fprint prints the (sub-)tree starting at AST node x to w. If fset != nil, position information is interpreted relative to that file set. Otherwise positions are printed as integer values (file set specific offsets).

A non-nil FieldFilter f may be provided to control the output: struct fields for which f(fieldname, fieldvalue) is true are printed; all others are filtered from the output. Unexported struct fields are never printed.

Golang go/ast.Fprint() function usage example

 ... 
 var fset = token.NewFileSet()

 file, err := parser.ParseFile(fset, "src.go", src, 0)
 if err != nil {
 fmt.Println(err)
 }

 var before bytes.Buffer
 ast.Fprint(&before, fset, file, nil) // <-- here
 ...

Reference :

http://golang.org/pkg/go/ast/#Fprint