com-lihaoyi fastparse basic usage examples / published by https://github.com/dacr/code-examples-manager #55d6e8db-aa22-47af-b8d8-dcffaf9cd257/2f6ffbd3da7ee9fd8e4807dce4e67aaf0b7170f7

com-lihaoyi-fastparse.sc

// 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 "3.6.4"
//> using dep "com.lihaoyi::fastparse:3.1.1"
// ---------------------

// 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, p => expr(using p))
evaluation match {
  case Parsed.Success(value, _) => println(s"$expression = $value")
  case Parsed.Failure(failure)  => println(failure)
}