Arithmetic evaluation: Difference between revisions
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(→{{header|Scala}}: Added simpler example, which doesn't follow all requirements) |
(→{{header|Scala}}: On a second thought, remove that code, for copyright reasons) |
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This example was made rather more complex by the requirement of generating an AST tree. |
This example was made rather more complex by the requirement of generating an AST tree. With a Scala distribution there are many examples of arithmetic parsers, as small as half a dozen lines. |
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<lang scala>/* __ *\ |
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** ________ ___ / / ___ Scala API ** |
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** / __/ __// _ | / / / _ | (c) 2006-2010, 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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}</lang> |
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=={{header|Tcl}}== |
=={{header|Tcl}}== |
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