Toy language with parser combinators of scala, which is derived from Kishida-san's code. Original language has dynamic scope. But It has static scope and so-called lexical closure.

MiniParser.scala

package miniparser

import scala.util.parsing.combinator.RegexParsers

object Main {

  def main(args: Array[String]): Unit = {
    val parser = new MiniParser
    println(parser.parse("12-5*3+7*(2+5)+0"))
  }

  trait AST
  case class AddOp(left: AST, right:AST)
  case class SubOp(left: AST, right:AST)
  case class MulOp(left: AST, right:AST)
  case class IntVal(value: Int)
  
  class MiniParser extends RegexParsers{
    //expr ::= add
    def expr: Parser[Any] = add
    //expr ::= term ["+" term | "-" term}.
    def add:  Parser[Any] = term~rep("+"~term|"-"~term)
    //term ::= factor {"*" factor}
    def term : Parser[Any] = factor~rep("*"~factor)
    //factor ::= intLiteral | "(" expr ")"
    def factor: Parser[Any] = intLiteral | "("~expr~")"
    //intLiteral ::= ["1"-"9"] {"0"-"9"}
    def intLiteral : Parser[Any] = """[1-9][0-9]*|0""".r
    
    def parse(str:String) = parseAll(expr, str)
  }
}