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/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2006-2010, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
package examples.parsing
import scala.util.parsing.combinator.lexical.StdLexical
import scala.util.parsing.combinator.syntactical.StdTokenParsers
/** Parse and evaluate a numeric expression as a sequence of terms, separated by + or -
* a term is a sequence of factors, separated by * or /
* a factor is a parenthesized expression or a number
*
* @author Adriaan Moors
*/
object arithmeticParser extends StdTokenParsers {
type Tokens = StdLexical ; val lexical = new StdLexical
lexical.delimiters ++= List("(", ")", "+", "-", "*", "/")
lazy val expr = term*("+" ^^^ {(x: int, y: int) => x + y} | "-" ^^^ {(x: int, y: int) => x - y})
lazy val term = factor*("*" ^^^ {(x: int, y: int) => x * y} | "/" ^^^ {(x: int, y: int) => x / y})
lazy val factor: Parser[int] = "(" ~> expr <~ ")" | numericLit ^^ (_.toInt)
def main(args: Array[String]) {
println(
if (args.length == 1) {
expr(new lexical.Scanner(args(0)))
}
else
"usage: scala examples.parsing.arithmeticParser <expr-string>"
)
}
}
object arithmeticParserDesugared extends StdTokenParsers {
type Tokens = StdLexical ; val lexical = new StdLexical
lexical.delimiters ++= List("(", ")", "+", "-", "*", "/")
lazy val expr = chainl1(term, (keyword("+").^^^{(x: int, y: int) => x + y}).|(keyword("-").^^^{(x: int, y: int) => x - y}))
lazy val term = chainl1(factor, (keyword("*").^^^{(x: int, y: int) => x * y}).|(keyword("/").^^^{(x: int, y: int) => x / y}))
lazy val factor: Parser[int] = keyword("(").~>(expr.<~(keyword(")"))).|(numericLit.^^(x => x.toInt))
def main(args: Array[String]) {
println(
if (args.length == 1) {
expr(new lexical.Scanner(args(0)))
}
else
"usage: scala examples.parsing.arithmeticParser <expr-string>"
)
}
}
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