Scala example source code file (TestParser.scala)

This example Scala source code file (TestParser.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

app, app, list, name, parser, parser, parseresult, ref, ref, stdlexical, stdtokenparsers, term, term, testparser

The Scala TestParser.scala source code

package examples.parsing.lambda

import scala.util.parsing.input.Reader
import scala.util.parsing.combinator.lexical.StdLexical
import scala.util.parsing.combinator.syntactical.StdTokenParsers
import scala.util.parsing.combinator.ImplicitConversions

/**
 * Parser for an untyped lambda calculus
 *
 * @author Miles Sabin (adapted slightly by Adriaan Moors)
 */
trait TestParser extends StdTokenParsers  with ImplicitConversions with TestSyntax
{
  type Tokens = StdLexical
  val lexical = new StdLexical
  lexical.reserved ++= List("unit", "let", "in", "if", "then", "else")
  lexical.delimiters ++= List("=>", "->", "==", "(", ")", "=", "\\", "+", "-", "*", "/")

  
	def name : Parser[Name] = ident ^^ Name
  
  // meaning of the arguments to the closure during subsequent iterations
  // (...(expr2 op1 expr1) ... op1 expr1)
  //      ^a^^^ ^o^ ^b^^^
  //      ^^^^^^^a^^^^^^^      ^o^ ^^b^^
  def expr1 : Parser[Term] =
    chainl1(expr2, expr1, op1 ^^ {o => (a: Term, b: Term) => App(App(o, a), b)})

  def expr2 : Parser[Term] =
   chainl1(expr3, expr2, op2 ^^ {o => (a: Term, b: Term) => App(App(o, a), b)})
  
  def expr3 : Parser[Term] =
   chainl1(expr4, expr3, op3 ^^ {o => (a: Term, b: Term) => App(App(o, a), b)})
  
  def expr4 : Parser[Term] =
  ( "\\" ~> lambdas
  | ("let" ~> name) ~ ("=" ~> expr1) ~ ("in" ~> expr1) ^^ flatten3(Let)
  | ("if" ~> expr1) ~ ("then" ~> expr1) ~ ("else" ~> expr1) ^^ flatten3(If)
  | chainl1(aexpr, success(App(_: Term, _: Term)))
  )

  def lambdas : Parser[Term] =
    name ~ ("->" ~> expr1 | lambdas) ^^ flatten2(Lam)
      
  def aexpr : Parser[Term] =
  ( numericLit ^^ (_.toInt) ^^ Lit
  | name ^^ Ref
  | "unit" ^^^ Unit()
  | "(" ~> expr1 <~ ")"
  )
  
  def op1 : Parser[Term] =
    "=="  ^^^ Ref(Name("=="))
  
  def op2 : Parser[Term] =
  ( "+" ^^^ Ref(Name("+"))
  | "-" ^^^ Ref(Name("-"))
  )
  
  def op3 : Parser[Term] =
  ( "*" ^^^ Ref(Name("*"))
  | "/" ^^^ Ref(Name("/"))
  )
  
  def parse(r: Reader[char]) : ParseResult[Term] =
    phrase(expr1)(new lexical.Scanner(r))
}