You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: print.go
    path of file: ./repos/gccrs/libgo/go/go/ast
    
    the code of the file until where you have to start completion: // Copyright 2010 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.

// This file contains printing support for ASTs.

package ast

import (
	"fmt"
	"go/token"
	"io"
	"os"
	"reflect"
)

// A FieldFilter may be provided to Fprint to control the output.
type FieldFilter func(name string, value reflect.Value) bool

// NotNilFilter returns true for field values that are not nil;
// it returns false otherwise.
func NotNilFilter(_ string, v reflect.Value) bool {
	switch v.Kind() {
	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Pointer, reflect.Slice:
		return !v.IsNil()
	}
	return true
}

// 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.
func Fprint(w io.Writer, fset *token.FileSet, x any, f FieldFilter) error {
	return fprint(w, fset, x, f)
}

func fprint(w io.Writer, fset *token.FileSet, x any, f FieldFilter) (err error) {
	// setup printer
	p := printer{
		output: w,
		fset:   fset,
		filter: f,
		ptrmap: make(map[any]int),
		last:   '\n', // force printing of line number on first line
	}

	// install error handler
	defer func() {
		if e := recover(); e != nil {
			err = e.(localError).err // re-panics if it's not a localError
		}
	}()

	// print x
	if x == nil {
		p.printf("nil\n")
		return
	}
	p.print(reflect.ValueOf(x))
	p.printf("\n")

	return
}

// Print prints x to standard output, skipping nil fields.
// Print(fset, x) is the same as Fprint(os.Stdout, fset, x, NotNilFilter).
func Print(fset *token.FileSet, x any) error {
	return Fprint(os.Stdout, fset, x, NotNilFilter)
}

type printer struct {
	output io.Writer
	fset   *token.Fil
    
func (p *printer) print(x reflect.Value) {
	if !NotNilFilter("", x) {
		p.printf("nil")
		return
	}

	switch x.Kind() {
	case reflect.Interface:
		p.print(x.Elem())

	case reflect.Map:
		p.printf("%s (len = %d) {", x.Type(), x.Len())
		if x.Len() > 0 {
			p.indent++
			p.printf("\n")
			for _, key := range x.MapKeys() {
				p.print(key)
				p.printf(": ")
				p.print(x.MapIndex(key))
				p.printf("\n")
			}
			p.indent--
		}
		p.printf("}")

	case reflect.Pointer:
		p.printf("*")
		// type-checked ASTs may contain cycles - use ptrmap
		// to keep track of objects that have been printed
		// already and print the respective line number instead
		ptr := x.Interface()
		if line, exists := p.ptrmap[ptr]; exists {
			p.printf("(obj @ %d)", line)
		} else {
			p.ptrmap[ptr] = p.line
			p.print(x.Elem())
		}

	case reflect.Array:
		p.printf("%s {", x.Type())
		if x.Len() > 0 {
			p.indent++
			p.printf("\n")
			for i, n := 0, x.Len(); i < n; i++ {
				p.printf("%d: ", i)
				p.print(x.Index(i))
				p.printf("\n")
			}
			p.indent--
		}
		p.printf("}")

	case reflect.Slice:
		if s, ok := x.Interface().([]byte); ok {
			p.printf("%#q", s)
			return
		}
		p.printf("%s (len = %d) {", x.Type(), x.Len())
		if x.Len() > 0 {
			p.indent++
			p.printf("\n")
			for i, n := 0, x.Len(); i < n; i++ {
				p.printf("%d: ", i)
				p.print(x.Index(i))
				p.printf("\n")
			}
			p.indent--
		}
		p.printf("}")

	case reflect.Struct:
		t := x.Type()
		p.printf("%s {", t)
		p.indent++
		first := true
		for i, n := 0, t.NumField(); i < n; i++ {
			// exclude non-exported fields because their
			// values cannot be accessed via reflection
			if name := t.Field(i).Name; IsExported(name) {
				value := x.Field(i)
				if p.filter == nil || p.filter(name, value) {
					if first {
						p.printf("\n")
						first = false
					}
					p.printf("%s: ", name)
					p.print(value)
					p.printf("\n")
				}
			}
		}
		p.indent--
		p.printf("}")

	default:
		v := x.Interface()
		switch v := v.(type) {
		case string:
			// print strings in quotes
			p.printf("%q", v)
			return
		case token.Pos:
			// position values can be printed nicely if we have a file set
			if p.fset != nil {
				p.printf("%s", p.fset.Position(v))
				return
			}
		}
		// default
		p.printf("%v", v)
	}
}