seperti https://gist.github.com/birowo/03889aced8ea20c422a45846f4b060a2 dengan penambahan type []struct {k string; v interface{}} untuk akses key-value secara sequential . playground: https://play.golang.org/p/ZZ5Ym8tGgOS

jsonmap.v2.go

package main

import (
	"bytes"
	"strconv"
)

func fKV(rslt *bytes.Buffer, v KV) {
	i := len(v)
	rslt.WriteByte('{')
	for _k, _v := range v {
		rslt.WriteByte('"')
		rslt.WriteString(_k)
		rslt.WriteString(`":`)
		Marshal(rslt, _v)
		i--
		if i == 0 {
			rslt.WriteByte('}')
			return
		}
		rslt.WriteByte(',')
	}
}
func fSlc(rslt *bytes.Buffer, v Slc) {
	last := len(v) - 1
	rslt.WriteByte('[')
	for _, _v := range v[:last] {
		Marshal(rslt, _v)
		rslt.WriteByte(',')
	}
	Marshal(rslt, v[last])
	rslt.WriteByte(']')
}
func fKVSeq(rslt *bytes.Buffer, v KVSeq) {
	last := len(v) - 1
	rslt.WriteByte('{')
	for _, _v := range v[:last] {
		rslt.WriteByte('"')
		rslt.WriteString(_v.k)
		rslt.WriteString(`":`)
		Marshal(rslt, _v.v)
		rslt.WriteByte(',')
	}
	rslt.WriteByte('"')
	rslt.WriteString(v[last].k)
	rslt.WriteString(`":`)
	Marshal(rslt, v[last].v)
	rslt.WriteByte('}')
}
func Marshal(rslt *bytes.Buffer, v interface{}) {
	switch v.(type) {
	case string:
		rslt.WriteByte('"')
		rslt.WriteString(v.(string))
		rslt.WriteByte('"')
	case int:
		rslt.WriteString(strconv.FormatInt(int64(v.(int)), 10))
	case float64:
		rslt.WriteString(strconv.FormatFloat(v.(float64), 'f', -1, 64))
	case KV:
		fKV(rslt, v.(KV))
	case Slc:
		fSlc(rslt, v.(Slc))
	case KVSeq:
		fKVSeq(rslt, v.(KVSeq))
	default:
		println("unsupported type")
	}
}

type (
	KV    map[string]interface{}
	Slc   []interface{}
	KVSeq []struct {
		k string
		v interface{}
	}
)

func main() {
	kvseq := KVSeq{
		{"a", 123},
		{"b", Slc{1, 2}},
		{"c", 1.23},
		{"d", Slc{1.2, 2.3}},
		{"e", KVSeq{{"a", 123}}},
		{"f", Slc{KVSeq{{"a", 12}}, KVSeq{{"b", 23}}}},
		{"g", "abc"},
		{"h", Slc{"ab", "bc"}},
	}
	var rslt2 bytes.Buffer
	Marshal(&rslt2, kvseq)
	println(rslt2.String())
}