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</pre>
This example was made rather more complex by the requirement of generating an AST tree. HereWith isa anScala arithmeticdistribution evaluatorthere usingare themany veryexamples sameof libraryarithmetic parsers, butas small notas boundedhalf bya thatdozen requirement:lines.
<lang scala>/* __ *\
** ________ ___ / / ___ 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>"
)
}
}</lang>
=={{header|Tcl}}==
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