58 lines
2.3 KiB
Scala
58 lines
2.3 KiB
Scala
/* __ *\
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** ________ ___ / / ___ Scala API **
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** / __/ __// _ | / / / _ | (c) 2006-2011, LAMP/EPFL **
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** __\ \/ /__/ __ |/ /__/ __ | **
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** /____/\___/_/ |_/____/_/ | | **
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** |/ **
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\* */
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package examples.parsing
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import scala.util.parsing.combinator.lexical.StdLexical
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import scala.util.parsing.combinator.syntactical.StdTokenParsers
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/** Parse and evaluate a numeric expression as a sequence of terms, separated by + or -
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* a term is a sequence of factors, separated by * or /
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* a factor is a parenthesized expression or a number
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*
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* @author Adriaan Moors
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*/
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object arithmeticParser extends StdTokenParsers {
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type Tokens = StdLexical ; val lexical = new StdLexical
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lexical.delimiters ++= List("(", ")", "+", "-", "*", "/")
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lazy val expr = term*("+" ^^^ {(x: int, y: int) => x + y} | "-" ^^^ {(x: int, y: int) => x - y})
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lazy val term = factor*("*" ^^^ {(x: int, y: int) => x * y} | "/" ^^^ {(x: int, y: int) => x / y})
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lazy val factor: Parser[int] = "(" ~> expr <~ ")" | numericLit ^^ (_.toInt)
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def main(args: Array[String]) {
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println(
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if (args.length == 1) {
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expr(new lexical.Scanner(args(0)))
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}
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else
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"usage: scala examples.parsing.arithmeticParser <expr-string>"
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)
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}
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}
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object arithmeticParserDesugared extends StdTokenParsers {
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type Tokens = StdLexical ; val lexical = new StdLexical
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lexical.delimiters ++= List("(", ")", "+", "-", "*", "/")
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lazy val expr = chainl1(term, (keyword("+").^^^{(x: int, y: int) => x + y}).|(keyword("-").^^^{(x: int, y: int) => x - y}))
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lazy val term = chainl1(factor, (keyword("*").^^^{(x: int, y: int) => x * y}).|(keyword("/").^^^{(x: int, y: int) => x / y}))
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lazy val factor: Parser[int] = keyword("(").~>(expr.<~(keyword(")"))).|(numericLit.^^(x => x.toInt))
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def main(args: Array[String]) {
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println(
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if (args.length == 1) {
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expr(new lexical.Scanner(args(0)))
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}
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else
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"usage: scala examples.parsing.arithmeticParser <expr-string>"
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)
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}
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}
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