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com-lihaoyi fastparse basic usage examples / published by https://github.com/dacr/code-examples-manager #55d6e8db-aa22-47af-b8d8-dcffaf9cd257/9f77ef93622bb59abe9df2257ddc1ff818478e19
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// summary : com-lihaoyi fastparse basic usage examples | |
// keywords : scala, lihaoyi, fastparse, @testable | |
// publish : gist | |
// authors : David Crosson | |
// license : Apache NON-AI License Version 2.0 (https://raw.githubusercontent.com/non-ai-licenses/non-ai-licenses/main/NON-AI-APACHE2) | |
// id : 55d6e8db-aa22-47af-b8d8-dcffaf9cd257 | |
// created-on : 2024-01-06T16:30:18+01:00 | |
// managed-by : https://github.com/dacr/code-examples-manager | |
// run-with : scala-cli $file | |
// --------------------- | |
//> using scala "3.4.2" | |
//> using dep "com.lihaoyi::fastparse:3.0.2" | |
// --------------------- | |
// This is largely inspired by the main example from https://com-lihaoyi.github.io/fastparse/ | |
import fastparse._, NoWhitespace._ | |
def number[$: P]: P[Int] = P(CharIn("0-9").rep(1).!.map(_.toInt)) | |
def parens[$: P]: P[Int] = P("(" ~/ addSub ~ ")") | |
def factor[$: P]: P[Int] = P(number | parens) | |
def divMul[$: P]: P[Int] = P(factor ~ (CharIn("*/").! ~/ factor).rep).map(eval) | |
def addSub[$: P]: P[Int] = P(divMul ~ (CharIn("+\\-").! ~/ divMul).rep).map(eval) | |
def expr[$: P]: P[Int] = P(addSub ~ End) | |
def eval(tree: (Int, Seq[(String, Int)])) = { | |
val (base, ops) = tree | |
ops.foldLeft(base) { case (left, (op, right)) => | |
op match { | |
case "+" => left + right | |
case "-" => left - right | |
case "*" => left * right | |
case "/" => left / right | |
} | |
} | |
} | |
val expression = "((1+1*2)+(3*4*5))/3" | |
val evaluation = parse(expression, expr(_)) | |
evaluation match { | |
case Parsed.Success(value, _) => println(s"$expression = $value") | |
case Parsed.Failure(failure) => println(failure) | |
} |
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