型なし言語のメリットを一言で書いてみる ref: https://qiita.com/kmizu/items/0892eca588088836967f

file0.scala

sealed abstract class JsonValue
case class JsonObject(val members: Map[String, JsonValue]) extends JsonValue
case class JsonNumber(val value: Int) extends JsonValue
case class JsonString(val value: String) extends JsonValue
...

file1.scala

sealed class JsonValue {
  data class JsonObject(val members: Map<String, JsonValue>) : JsonValue()
  data class JsonNumber(val value: Int) : JsonValue()
  data class JsonString(val value: String) : JsonValue()
  ...
}

file2.java

import java.util.*;
public class Json {
        public static abstract class JsonValue {}
        public static class JsonObject extends JsonValue {
                public final Map<String,JsonValue> members; 
                public JsonObject(Map<String, JsonValue> members) {
                        this.members = members;
                }
        }
        public static class JsonNumber extends JsonValue {
                public final int value;
                public JsonNumber(int value) {
                        this.value = value;
                }
        }
        public static class JsonString extends JsonValue {
                public final String value;
                public JsonString(String value) {
                        this.value = value;
                }
        }
        ...
}

file3.txt

import qualified Data.Map as M
data JsonValue = JsonObject { members:: M.Map String JsonValue }
               | JsonNumber Int
               | ...
               | JsonString String deriving Show

file4.txt

{ "name" : "Taro", "age": 30 }

file5.scala

val person: JsonObject = ...
val name: String = person.members("name").asInstanceOf[JsonString].value
val age: Int = person.members("age").asInstanceOf[JsonNumber].value
println(name)
println(age + 1)
...

file6.scala

println(person.name)
println(person.age + 1)

file7.scala

person.age + 1

file8.txt

person.age + 1

file9.txt

(+ (get-age person) 1)