andimiller / cats-parse-interpolator   0.1.0

GitHub
Scala versions: 3.x 2.13 2.12
Scala.js versions: 1.x
Scala Native versions: 0.4

cats-parse-interpolator

This library adds a parser interpolator to make cats-parse slightly easier to use.

Included Interpolators:

Prefix Description Inputs Output
p Parser Applicative all Parser Parser
p0 Parser0 Applicative all Parser0 Parser0
pm Parser Monad Parser, then either afterwards Parser

Usage

libraryDependencies += "net.andimiller" %% "cats-parse-interpolator" % "0.1.0"

You then import the library, and probably cats.parse too

import net.andimiller.cats.parse.interpolator._
import cats.parse._
import cats.implicits._ // if you need extra syntax

Then you can create a parser with a p prefix like so:

p"hello world".parseAll("hello world")
// res0: Either[Error, Unit] = Right(value = ())

You can interpolate other parsers into it:

{
  val name = Parser.charsWhile(_.isLetter)
  val number = Parser.charsWhile(_.isDigit).map(_.toInt)
  p"$name = $number".parseAll("bob = 10")
}
// res1: Either[Error, Tuple2[String, Int]] = Right(value = ("bob", 10))

And it will even type the output correctly as a tuple of all subparsers.

There is also an interpreter for Parser0 if you need that:

{
  val name = Parser.charsWhile0(_.isLetter).map(s => Option(s).filter(_.nonEmpty))
  val number = Parser.charsWhile0(_.isDigit).map(s => if (s.isEmpty) 0 else s.toInt)
  p0"$name = $number".parseAll(" = ")
}
// res2: Either[Error, Tuple2[Option[String], Int]] = Right(value = (None, 0))

Motivation

LISP Calculator Example

For a simple example, say we want to parse these:

val calculatorInputs = List(
  "(+ 2 2)",
  "(+ 2 (* 3 6))",
  "42"
)

Into these:

enum Expr:
  case Number(value: Int)
  case Plus(left: Expr, right: Expr)
  case Multiply(left: Expr, right: Expr)
Standard Interpolator 
calculatorInputs.map {
  Parser.recursive[Expr] { recurse =>
    val number   = Numbers.digits.map(_.toInt).map(Expr.Number)  
    val plus     = (
                     Parser.string("(+ ") *> recurse <* Parser.string(" "), 
                     recurse <* Parser.string(")")
                   ).mapN(Expr.Plus)
    val multiply = (
                     Parser.string("(* ") *> recurse <* Parser.string(" "), 
                     recurse <* Parser.string(")")
                   ).mapN(Expr.Multiply)
    number.orElse(plus).orElse(multiply)
  }.parseAll
}
// res3: List[Either[Error, Expr]] = List(
//   Right(value = Plus(left = Number(value = 2), right = Number(value = 2))),
//   Right(
//     value = Plus(
//       left = Number(value = 2),
//       right = Multiply(left = Number(value = 3), right = Number(value = 6))
//     )
//   ),
//   Right(value = Number(value = 42))
// )
 
calculatorInputs.map {
  Parser.recursive[Expr] { recurse =>
    val number   = Numbers.digits.map(_.toInt).map(Expr.Number)  
    val plus     = p"(+ $recurse $recurse)".map(Expr.Plus)
    val multiply = p"(* $recurse $recurse)".map(Expr.Multiply)
    number.orElse(plus).orElse(multiply)
  }.parseAll
}
// res4: List[Either[Error, Expr]] = List(
//   Right(value = Plus(left = Number(value = 2), right = Number(value = 2))),
//   Right(
//     value = Plus(
//       left = Number(value = 2),
//       right = Multiply(left = Number(value = 3), right = Number(value = 6))
//     )
//   ),
//   Right(value = Number(value = 42))
// )

Env Variable Example

For a more complex parser, here's a parser for env variables, taking input like:

val envVars = "FOO=abcC,BAR=def"
Standard Interpolator 
{
  val keyStartChars = ('a' to 'z').toSet ++ ('A' to 'Z').toSet ++ "_".toSet
  val keyRestChars = keyStartChars ++ ('0' to '9').toSet
  val key = for {
    head <- Parser.charIn(keyStartChars).string
    rest <- Parser.charsWhile0(keyRestChars).string
  } yield head + rest
  val value = Parser.charsWhile(c => !" ,".toSet(c))

  val pair = for {
    k <- key
    _ <- Parser.char('=')
    v <- value
  } yield (k -> v)

  pair.repSep(Parser.char(','))
}.parseAll(envVars)
// res5: Either[Error, NonEmptyList[Tuple2[String, String]]] = Right(
//   value = NonEmptyList(head = ("FOO", "abcC"), tail = List(("BAR", "def")))
// )
 
{
  val keyStartChars = ('a' to 'z').toSet ++ ('A' to 'Z').toSet ++ "_".toSet

  val keyStart = Parser.charIn(keyStartChars).string
  val keyRest  = Parser.charsWhile0(keyStartChars ++ ('0' to '9').toSet).string

  val key   = pm"$keyStart$keyRest".string
  val value = Parser.charsWhile(c => !" ,".toSet(c))

  p"$key=$value".repSep(Parser.char(','))
}.parseAll(envVars)
// res6: Either[Error, NonEmptyList[Tuple2[String, String]]] = Right(
//   value = NonEmptyList(head = ("FOO", "abcC"), tail = List(("BAR", "def")))
// )

Statistics

7 Dependencies

No Dependent