Scala example source code file (MiniML.scala)

This example Scala source code file (MiniML.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Scala tags/keywords

apply, array, expr, expr, lambda, lambda, let, miniml, parser, parser, standardtokenparsers, string, string, var

The Scala MiniML.scala source code

package examples.parsing

import scala.util.parsing.combinator1.syntactical.StandardTokenParsers
import scala.util.parsing.combinator1.syntactical.StandardTokenParsers

object MiniML extends StandardTokenParsers {   
  lexical.delimiters += ("(", ")", ".", "=")
  lexical.reserved += ("lambda", "let", "in")

  def expr: Parser[Any] = (
    "let" ~ ident ~ "=" ~ expr ~ "in" ~ expr
  | "lambda" ~ ident ~ "." ~ expr
  | simpleExpr ~ rep(expr)
  )
  def simpleExpr: Parser[Any] = (
    ident
  | "(" ~ expr ~ ")"
  )

  def main(args: Array[String]) {
    val tokens = new lexical.Scanner(args(0))
    println(args(0))
    println(phrase(expr)(tokens))
  }
}

class Expr
case class Let(x: String, expr: Expr, body: Expr) extends Expr
case class Lambda(x: String, expr: Expr) extends Expr
case class Apply(fun: Expr, arg: Expr) extends Expr
case class Var(x: String) extends Expr

object MiniML1 extends StandardTokenParsers {   
  lexical.delimiters += ("(", ")", ".", "=")
  lexical.reserved += ("lambda", "let", "in")

  def expr: Parser[Expr] = (
    "let" ~ ident ~ "=" ~ expr ~ "in" ~ expr ^^ { case "let" ~ x ~ "=" ~ e ~ "in" ~ b => Let(x, e, b) }
  | "lambda" ~ ident ~ "." ~ expr            ^^ { case "lambda" ~ x ~ "." ~ e => Lambda(x, e) }
  | simpleExpr ~ rep(expr)                   ^^ { case f ~ as => (f /: as) (Apply) }
  )
  def simpleExpr: Parser[Expr] = (
    ident                                    ^^ { Var }
  | "(" ~> expr <~ ")"                       
  )

  def main(args: Array[String]) {
    val tokens = new lexical.Scanner(args(0))
    println(args(0))
    println(phrase(expr)(tokens))
  }
}