Папа Стифлера

package main

import "fmt"
import "regexp"

var IsLetter = regexp.MustCompile(`^[a-zA-Z]+$`).MatchString

func main() {
    fmt.Println(IsLetter("golang")) // true
    fmt.Println(IsLetter("рои134432-=-!№;;")) // false
}

The language specifies that if *T implements the methods of an interface I then only a
*T (pointer) value will satisfy I, and not a T (value) value. So encoding/json can't see
that *DecimalE8 implements MarshalJSON because it only has a DecimalE8 value.
It is important to preserve this property, because a value implemented on *T might
assume that it can modify the underlying T value (which, given a value receiver, it
could not).

data, err := json.Marshal(body)
if err != nil {
    log.Println(err)
}

w.Header().Add("Content-Type", "application/json")
w.WriteHeader(http.StatusOK)
_, _ = w.Write(data)