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copied!<p>Not easily, because a successful match is not retried. Consider, for example:</p> <pre><code>object X extends RegexParsers { def p = ("a" | "aa" | "aaa" | "aaaa") ~ "ab" } scala> X.parseAll(X.p, "aaaab") res1: X.ParseResult[X.~[String,String]] = [1.2] failure: `ab' expected but `a' found aaaab ^ </code></pre> <p>The first match was successful, in parser inside parenthesis, so it proceeded to the next one. That one failed, so <code>p</code> failed. If <code>p</code> was part of alternative matches, the alternative would be tried, so the trick is to produce something that can handle that sort of thing.</p> <p>Let's say we have this:</p> <pre><code>def nonGreedy[T](rep: => Parser[T], terminal: => Parser[T]) = Parser { in => def recurse(in: Input, elems: List[T]): ParseResult[List[T] ~ T] = terminal(in) match { case Success(x, rest) => Success(new ~(elems.reverse, x), rest) case _ => rep(in) match { case Success(x, rest) => recurse(rest, x :: elems) case ns: NoSuccess => ns } } recurse(in, Nil) } </code></pre> <p>You can then use it like this:</p> <pre><code>def p = nonGreedy("a", "ab") </code></pre> <p>By the way,I always found that looking at how other things are defined is helpful in trying to come up with stuff like <code>nonGreedy</code> above. In particular, look at how <code>rep1</code> is defined, and how it was changed to avoid re-evaluating its repetition parameter -- the same thing would probably be useful on <code>nonGreedy</code>.</p> <p>Here's a full solution, with a little change to avoid consuming the "terminal".</p> <pre><code>trait NonGreedy extends Parsers { def nonGreedy[T, U](rep: => Parser[T], terminal: => Parser[U]) = Parser { in => def recurse(in: Input, elems: List[T]): ParseResult[List[T]] = terminal(in) match { case _: Success[_] => Success(elems.reverse, in) case _ => rep(in) match { case Success(x, rest) => recurse(rest, x :: elems) case ns: NoSuccess => ns } } recurse(in, Nil) } } class Arith extends RegexParsers with NonGreedy { // Just to avoid recompiling the pattern each time val select: Parser[String] = "(?i)SELECT".r val from: Parser[String] = "(?i)FROM".r val token: Parser[String] = "(\\s*)\\w+(\\s*)".r val eof: Parser[String] = """\z""".r def selectstatement: Parser[Any] = selectclause(from) ~ fromclause(eof) def selectclause(terminal: Parser[Any]): Parser[Any] = select ~ tokens(terminal) def fromclause(terminal: Parser[Any]): Parser[Any] = from ~ tokens(terminal) def tokens(terminal: Parser[Any]): Parser[Any] = nonGreedy(token, terminal) } </code></pre>

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