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import scala.language.{ higherKinds, implicitConversions, postfixOps }
trait Parsers {
type Input = List[Char]
sealed class ParseResult[+t](val next: Input)
case class Success[+t](override val next: Input, result: t) extends ParseResult[t](next)
case class Failure(override val next: Input, msg: String) extends ParseResult[Nothing](next)
abstract class Parser[+t] {
def apply(in: Input): ParseResult[t]
}
// sequence
def sq[T, U](a: => Parser[T], b: => Parser[U]): Parser[Tuple2[T, U]] = new Parser[Tuple2[T, U]] {
def apply(in: Input): ParseResult[Tuple2[T, U]] = a(in) match {
case Success(next, x) => b(next) match {
case Success(next2, y) => Success(next2, (x,y))
case Failure(_, msg) => Failure(in, msg)
}
case Failure(_, msg) => Failure(in, msg)
}
}
// ordered choice
def or[T, U <: T](a: => Parser[T], b: => Parser[U]): Parser[T] = new Parser[T] {
def apply(in: Input): ParseResult[T] = a(in) match {
case Success(next, x) => Success(next, x)
case Failure(_, _) => b(in) match {
case Success(next, y) => Success(next, y)
case Failure(_, msg) => Failure(in, msg)
}
}
}
// lifting
def lift[T, U](f: T => U)(a: => Parser[T]): Parser[U] = new Parser[U] {
def apply(in: Input): ParseResult[U] = a(in) match {
case Success(n, x) => Success(n, f(x))
case Failure(n, msg) => Failure(n, msg)
}
}
def accept[T](c: Char, r: T): Parser[T] = new Parser[T] {
def apply(in: Input) = in match {
case c2 :: n if c2 == c => Success(n, r)
case n => Failure(n, "expected "+c+" at the head of "+n)
}
}
def apply_++[s, tt](fun: Parser[s => tt], arg: Parser[s]): Parser[tt] = lift[Tuple2[s=>tt, s], tt]({case (f, a) => f(a)})(sq(fun, arg))
def success[u](v: u): Parser[u] = new Parser[u] {
def apply(in: Input) = Success(in, v)
}
}
trait Idioms {
trait Idiom[idi[x]] {
def liftedApply[s, t](fun: idi[s => t])(arg: idi[s]): idi[t]
def pure[a](x: a): idi[a]
def pureMethod[a](name: String, x: a): idi[a] = pure(x) // hack for Mirrors: allow passing of method names
}
class IdiomaticTarget[idi[x], idiom <: Idiom[idi], s](i: idiom, tgt: s) {
def dot [t](fun: s => t, name: String) = new IdiomaticApp2[idi, idiom, t](i, i.liftedApply(i.pureMethod(name, fun))(i.pure(tgt)))
} // TODO: `.` --> java.lang.ClassFormatError: Illegal method name "." in class Idioms$Id$
class IdiomaticFunction[idi[x], idiom <: Idiom[idi], s, t](i: idiom, fun: s => t) {
def <| (a: idi[s]) = new IdiomaticApp[idi, idiom, t](i, i.liftedApply(i.pure(fun))(a))
}
class IdiomaticApp[idi[x], idiom <: Idiom[idi], x](i: idiom, a: idi[x]) {
// where x <: s=>t -- TODO can this be expressed without generalised constraints?
def <> [s, t](b: idi[s]) = new IdiomaticApp[idi, idiom, t](i, i.liftedApply(a.asInstanceOf[idi[s=>t]])(b))
def |> : idi[x] = a
}
class IdiomaticApp2[idi[x], idiom <: Idiom[idi], x](i: idiom, a: idi[x]) extends IdiomaticApp[idi, idiom, x](i, a) {
def <| [s, t](b: idi[s]) = <>[s,t](b)
}
}
trait ParserIdioms extends Parsers with Idioms {
object ParserIdiom extends Idiom[Parser] {
def liftedApply[s, t](fun: Parser[s => t])(arg: Parser[s]): Parser[t] = apply_++(fun, arg)
def pure[a](x: a): Parser[a] = success(x)
}
implicit def parserIdiomFun[s, t](fun: s=>t): IdiomaticFunction[Parser, ParserIdiom.type, s, t] =
new IdiomaticFunction[Parser, ParserIdiom.type, s, t](ParserIdiom, fun)
implicit def parserIdiomTgt[s](tgt: s): IdiomaticTarget[Parser, ParserIdiom.type, s] =
new IdiomaticTarget[Parser, ParserIdiom.type, s](ParserIdiom, tgt)
trait Expr
case class Plus(a: Int, b: Int) extends Expr
def num = or(accept('0', 0), or(accept('1', 1),accept('2', 2)))
// TODO: how can parserIdiom(curry2(_)) be omitted?
def expr: Parser[Expr] = parserIdiomFun(curry2(Plus)) <| num <> num |>
implicit def curry2[s,t,u](fun: (s, t)=>u)(a: s)(b: t): u = fun(a, b)
implicit def curry3[r,s,t,u](fun: (r,s, t)=>u)(a: r)(b: s)(c: t): u = fun(a, b, c)
}
object Test extends ParserIdioms with App {
assert(expr("12".toList).toString == "Success(List(),Plus(1,2))")
}
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