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package examples;
module Parse {
type Result = Option[List[Char]];
trait Parser extends Function1[List[Char],Result] with {
def &&& (def p: Parser) = new Parser {
def apply(in: List[Char]) = Parser.this.apply(in) match {
case Some(in1) => p(in1)
case n => n
}
}
def ||| (def p: Parser) = new Parser {
def apply(in: List[Char]) = Parser.this.apply(in) match {
case None() => p(in)
case s => s
}
}
}
val empty = new Parser { def apply(in: List[Char]): Result = Some(in) }
def fail = new Parser { def apply(in: List[Char]): Result = None() }
def chrWith(p: Char => Boolean) = new Parser {
def apply(in: List[Char]): Result = in match {
case List() => None()
case (c :: in1) => if (p(c)) Some(in1) else None()
}
}
def chr(c: Char): Parser = chrWith(d => d == c);
def opt(p: Parser): Parser = p ||| empty;
def rep(p: Parser): Parser = opt(rep1(p));
def rep1(p: Parser): Parser = p &&& rep(p);
}
module ExprParser {
import Parse._;
def letter = chrWith(c => c.isLetter);
def digit = chrWith(c => c.isDigit);
def ident = letter &&& rep(letter ||| digit);
def number = digit &&& rep(digit);
def expr:Parser = expr1 &&& rep((chr('+') &&& expr1) ||| (chr('-') &&& expr1));
def expr1 = expr2 &&& rep((chr('*') &&& expr2) ||| (chr('/') &&& expr2));
def expr2 = ident ||| number ||| (chr('(') &&& expr &&& chr(')'));
}
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