Rot13 in golang (exercise from tour)

exercise-rot-reader.go

package main

import (
        "io"
        "os"
        "strings"
)

type rot13Reader struct {
        reader io.Reader
}

func (rot *rot13Reader) Read(p []byte) (int, error) {
        n, err := rot.reader.Read(p)
        for i, char := range p {
                if (char >= 'A' && char < 'N') || (char >= 'a' && char < 'n') {
                        p[i] += 13
                } else if (char > 'M' && char <= 'Z') || (char > 'm' && char <= 'z') {
                        p[i] -= 13
                }
        }
        return n, err
}

func main() {
        s := strings.NewReader("Lbh penpxrq gur pbqr!")
        r := rot13Reader{s}
        io.Copy(os.Stdout, &r)
}