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Scala example source code file (Parsers.scala)
This example Scala source code file (Parsers.scala) is included in the DevDaily.com
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The Scala Parsers.scala source code
/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2006-2011, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
package scala.util.parsing.combinator
import scala.util.parsing.input._
import scala.collection.mutable.ListBuffer
import scala.annotation.tailrec
import annotation.migration
// TODO: better error handling (labelling like parsec's <?>)
/** <p>
* <code>Parsers is a component that provides generic
* parser combinators.
* </p>
* <p>
* It <i>requires the type of the elements these parsers should parse
* (each parser is polymorphic in the type of result it produces).
* </p>
* <p>
* There are two aspects to the result of a parser: (1) success or failure,
* and (2) the result. A <code>Parser[T] provides both kinds of
* information.
* </p>
* <p>
* The term ``parser combinator'' refers to the fact that these parsers
* are constructed from primitive parsers and composition operators, such
* as sequencing, alternation, optionality, repetition, lifting, and so on.
* </p>
* <p>
* A ``primitive parser'' is a parser that accepts or rejects a single
* piece of input, based on a certain criterion, such as whether the
* input...
* </p>
* <li> is equal to some given object,
* <li> satisfies a certain predicate,
* <li> is in the domain of a given partial function,....
* </ul>
* <p>
* Even more primitive parsers always produce the same result, irrespective
* of the input.
* </p>
*
* @author Martin Odersky, Iulian Dragos, Adriaan Moors
*/
trait Parsers {
/** the type of input elements the provided parsers consume (When consuming invidual characters, a parser is typically
* called a ``scanner'', which produces ``tokens'' that are consumed by what is normally called a ``parser''.
* Nonetheless, the same principles apply, regardless of the input type.) */
type Elem
/** The parser input is an abstract reader of input elements, i.e. the type of input the parsers in this component
* expect. */
type Input = Reader[Elem]
/** A base class for parser results. A result is either successful or not (failure may be fatal, i.e., an Error, or
* not, i.e., a Failure). On success, provides a result of type `T` which consists of some result (and the rest of
* the input). */
sealed abstract class ParseResult[+T] {
/** Functional composition of ParseResults
*
* @param `f' the function to be lifted over this result
* @return `f' applied to the result of this `ParseResult', packaged up as a new `ParseResult'
*/
def map[U](f: T => U): ParseResult[U]
/** Partial functional composition of ParseResults
*
* @param `f' the partial function to be lifted over this result
* @param error a function that takes the same argument as `f' and produces an error message
* to explain why `f' wasn't applicable (it is called when this is the case)
* @return <i>if `f' f is defined at the result in this `ParseResult',
* `f' applied to the result of this `ParseResult', packaged up as a new `ParseResult'.
* If `f' is not defined, `Failure'.
*/
def mapPartial[U](f: PartialFunction[T, U], error: T => String): ParseResult[U]
def flatMapWithNext[U](f: T => Input => ParseResult[U]): ParseResult[U]
def append[U >: T](a: => ParseResult[U]): ParseResult[U]
def isEmpty = !successful
/** Returns the embedded result */
def get: T
def getOrElse[B >: T](default: => B): B =
if (isEmpty) default else this.get
val next: Input
val successful: Boolean
}
/** The success case of ParseResult: contains the result and the remaining input.
*
* @param result The parser's output
* @param next The parser's remaining input
*/
case class Success[+T](result: T, override val next: Input) extends ParseResult[T] {
def map[U](f: T => U) = Success(f(result), next)
def mapPartial[U](f: PartialFunction[T, U], error: T => String): ParseResult[U]
= if(f.isDefinedAt(result)) Success(f(result), next)
else Failure(error(result), next)
def flatMapWithNext[U](f: T => Input => ParseResult[U]): ParseResult[U]
= f(result)(next)
def append[U >: T](a: => ParseResult[U]): ParseResult[U] = this
def get: T = result
/** The toString method of a Success */
override def toString = "["+next.pos+"] parsed: "+result
val successful = true
}
var lastNoSuccess: NoSuccess = null
/** A common super-class for unsuccessful parse results
*/
sealed abstract class NoSuccess(val msg: String, override val next: Input) extends ParseResult[Nothing] { // when we don't care about the difference between Failure and Error
val successful = false
if (!(lastNoSuccess != null && next.pos < lastNoSuccess.next.pos))
lastNoSuccess = this
def map[U](f: Nothing => U) = this
def mapPartial[U](f: PartialFunction[Nothing, U], error: Nothing => String): ParseResult[U] = this
def flatMapWithNext[U](f: Nothing => Input => ParseResult[U]): ParseResult[U]
= this
def get: Nothing = sys.error("No result when parsing failed")
}
/** An extractor so NoSuccess(msg, next) can be used in matches.
*/
object NoSuccess {
def unapply[T](x: ParseResult[T]) = x match {
case Failure(msg, next) => Some(msg, next)
case Error(msg, next) => Some(msg, next)
case _ => None
}
}
/** The failure case of ParseResult: contains an error-message and the remaining input.
* Parsing will back-track when a failure occurs.
*
* @param msg An error message string describing the failure.
* @param next The parser's unconsumed input at the point where the failure occurred.
*/
case class Failure(override val msg: String, override val next: Input) extends NoSuccess(msg, next) {
/** The toString method of a Failure yields an error message */
override def toString = "["+next.pos+"] failure: "+msg+"\n\n"+next.pos.longString
def append[U >: Nothing](a: => ParseResult[U]): ParseResult[U] = { val alt = a; alt match {
case Success(_, _) => alt
case ns: NoSuccess => if (alt.next.pos < next.pos) this else alt
}}
}
/** The fatal failure case of ParseResult: contains an error-message and the remaining input.
* No back-tracking is done when a parser returns an `Error'
*
* @param msg An error message string describing the error.
* @param next The parser's unconsumed input at the point where the error occurred.
*/
case class Error(override val msg: String, override val next: Input) extends NoSuccess(msg, next) {
/** The toString method of an Error yields an error message */
override def toString = "["+next.pos+"] error: "+msg+"\n\n"+next.pos.longString
def append[U >: Nothing](a: => ParseResult[U]): ParseResult[U] = this
}
def Parser[T](f: Input => ParseResult[T]): Parser[T]
= new Parser[T]{ def apply(in: Input) = f(in) }
def OnceParser[T](f: Input => ParseResult[T]): Parser[T] with OnceParser[T]
= new Parser[T] with OnceParser[T] { def apply(in: Input) = f(in) }
/** The root class of parsers.
* Parsers are functions from the Input type to ParseResult
*/
abstract class Parser[+T] extends (Input => ParseResult[T]) {
private var name: String = ""
def named(n: String): this.type = {name=n; this}
override def toString() = "Parser ("+ name +")"
/** An unspecified method that defines the behaviour of this parser.
*/
def apply(in: Input): ParseResult[T]
def flatMap[U](f: T => Parser[U]): Parser[U]
= Parser{ in => this(in) flatMapWithNext(f)}
def map[U](f: T => U): Parser[U] //= flatMap{x => success(f(x))}
= Parser{ in => this(in) map(f)}
// no filter yet, dealing with zero is tricky!
@migration(2, 9, "As of 2.9, the call-by-name argument is evaluated at most once per constructed Parser object, instead of on every need that arises during parsing.")
def append[U >: T](p0: => Parser[U]): Parser[U] = { lazy val p = p0 // lazy argument
Parser{ in => this(in) append p(in)}
}
// the operator formerly known as +++, ++, &, but now, behold the venerable ~
// it's short, light (looks like whitespace), has few overloaded meaning (thanks to the recent change from ~ to unary_~)
// and we love it! (or do we like `,` better?)
/** A parser combinator for sequential composition
*
* <p> `p ~ q' succeeds if `p' succeeds and `q' succeeds on the input
* left over by `p'.</p>
*
* @param q a parser that will be executed after `p' (this parser) succeeds -- evaluated at most once, and only when necessary
* @return a `Parser' that -- on success -- returns a `~' (like a Pair, but easier to pattern match on)
* that contains the result of `p' and that of `q'.
* The resulting parser fails if either `p' or `q' fails.
*/
@migration(2, 9, "As of 2.9, the call-by-name argument is evaluated at most once per constructed Parser object, instead of on every need that arises during parsing.")
def ~ [U](q: => Parser[U]): Parser[~[T, U]] = { lazy val p = q // lazy argument
(for(a <- this; b <- p) yield new ~(a,b)).named("~")
}
/** A parser combinator for sequential composition which keeps only the right result
*
* <p> `p ~> q' succeeds if `p' succeeds and `q' succeeds on the input
* left over by `p'.</p>
*
* @param q a parser that will be executed after `p' (this parser) succeeds -- evaluated at most once, and only when necessary
* @return a `Parser' that -- on success -- returns the result of `q'.
*/
@migration(2, 9, "As of 2.9, the call-by-name argument is evaluated at most once per constructed Parser object, instead of on every need that arises during parsing.")
def ~> [U](q: => Parser[U]): Parser[U] = { lazy val p = q // lazy argument
(for(a <- this; b <- p) yield b).named("~>")
}
/** A parser combinator for sequential composition which keeps only the left result
*
* <p> `p <~ q' succeeds if `p' succeeds and `q' succeeds on the input
* left over by `p'.</p>
*
* <b>Note: <~ has lower operator precedence than ~ or ~>.
*
* @param q a parser that will be executed after `p' (this parser) succeeds -- evaluated at most once, and only when necessary
* @return a `Parser' that -- on success -- returns the result of `p'.
*/
@migration(2, 9, "As of 2.9, the call-by-name argument is evaluated at most once per constructed Parser object, instead of on every need that arises during parsing.")
def <~ [U](q: => Parser[U]): Parser[T] = { lazy val p = q // lazy argument
(for(a <- this; b <- p) yield a).named("<~")
}
/* not really useful: V cannot be inferred because Parser is covariant in first type parameter (V is always trivially Nothing)
def ~~ [U, V](q: => Parser[U])(implicit combine: (T, U) => V): Parser[V] = new Parser[V] {
def apply(in: Input) = seq(Parser.this, q)((x, y) => combine(x,y))(in)
} */
/** A parser combinator for non-back-tracking sequential composition
*
*<p>`p ~! q' succeeds if `p' succeeds and `q' succeeds on the input
* left over by `p'. In case of failure, no back-tracking is performed
* (in an earlier parser produced by the | combinator).</p>
*
* @param q a parser that will be executed after `p' (this parser) succeeds
* @return a `Parser' that -- on success -- returns a `~' (like a Pair, but easier to pattern match on)
* that contains the result of `p' and that of `q'.
* The resulting parser fails if either `p' or `q' fails, this failure is fatal.
*/
def ~! [U](p: => Parser[U]): Parser[~[T, U]]
= OnceParser{ (for(a <- this; b <- commit(p)) yield new ~(a,b)).named("~!") }
/** A parser combinator for alternative composition
*
*<p>`p | q' succeeds if `p' succeeds or `q' succeeds
* Note that `q' is only tried if `p's failure is non-fatal (i.e., back-tracking is
* allowed).</p>
*
* @param q a parser that will be executed if `p' (this parser) fails (and allows back-tracking)
* @return a `Parser' that returns the result of the first parser to succeed (out of `p' and `q')
* The resulting parser succeeds if (and only if) <ul>
* <li> `p' succeeds, or
* <li> if `p' fails allowing back-tracking and `q' succeeds.
*/
def | [U >: T](q: => Parser[U]): Parser[U] = append(q).named("|")
// TODO
/** A parser combinator for alternative with longest match composition
*
*<p>`p ||| q' succeeds if `p' succeeds or `q' succeeds
* If `p' and `q' both succeed, the parser that consumed the most
* characters accepts.</p>
*
* @param q0 a parser that accepts if p consumes less characters. -- evaluated at most once, and only when necessary
* @return a `Parser' that returns the result of the parser consuming the most characters (out of `p' and `q').
*/
@migration(2, 9, "As of 2.9, the call-by-name argument is evaluated at most once per constructed Parser object, instead of on every need that arises during parsing.")
def ||| [U >: T](q0: => Parser[U]): Parser[U] = new Parser[U] {
lazy val q = q0 // lazy argument
def apply(in: Input) = {
val res1 = Parser.this(in)
val res2 = q(in)
(res1, res2) match {
case (s1 @ Success(_, next1), s2 @ Success(_, next2)) => if (next2.pos < next1.pos) s1 else s2
case (s1 @ Success(_, _), _) => s1
case (_, s2 @ Success(_, _)) => s2
case (e1 @ Error(_, _), _) => e1
case (f1 @ Failure(_, next1), ns2 @ NoSuccess(_, next2)) => if (next2.pos < next1.pos) f1 else ns2
}
}
override def toString = "|||"
}
/** A parser combinator for function application
*
*<p>`p ^^ f' succeeds if `p' succeeds; it returns `f' applied to the result of `p'.
*
* @param f a function that will be applied to this parser's result (see `map' in `ParseResult').
* @return a parser that has the same behaviour as the current parser, but whose result is
* transformed by `f'.
*/
def ^^ [U](f: T => U): Parser[U] = map(f).named(toString+"^^")
/** A parser combinator that changes a successful result into the specified value.
*
* <p>`p ^^^ v' succeeds if `p' succeeds; discards its result, and returns `v` instead.
* @param v The new result for the parser, evaluated at most once (if `p` succeeds), not evaluated at all if `p` fails.
* @return a parser that has the same behaviour as the current parser, but whose successful result is `v`
*/
@migration(2, 9, "As of 2.9, the call-by-name argument is evaluated at most once per constructed Parser object, instead of on every need that arises during parsing.")
def ^^^ [U](v: => U): Parser[U] = new Parser[U] {
lazy val v0 = v // lazy argument
def apply(in: Input) = Parser.this(in) map (x => v0)
}.named(toString+"^^^")
/** A parser combinator for partial function application
*
*<p>`p ^? (f, error)' succeeds if `p' succeeds AND `f' is defined at the result of `p';
* in that case, it returns `f' applied to the result of `p'. If `f' is not applicable,
* error(the result of `p') should explain why.</p>
*
* @param f a partial function that will be applied to this parser's result
* (see `mapPartial' in `ParseResult').
* @param error a function that takes the same argument as `f' and produces an error message
* to explain why `f' wasn't applicable
* @return a parser that succeeds if the current parser succeeds <i>and `f' is applicable
* to the result. If so, the result will be transformed by `f'.
*/
def ^? [U](f: PartialFunction[T, U], error: T => String): Parser[U] = Parser{ in =>
this(in).mapPartial(f, error)}.named(toString+"^?")
/** A parser combinator for partial function application
*
*<p>`p ^? f' succeeds if `p' succeeds AND `f' is defined at the result of `p';
* in that case, it returns `f' applied to the result of `p'.</p>
*
* @param f a partial function that will be applied to this parser's result
* (see `mapPartial' in `ParseResult').
* @return a parser that succeeds if the current parser succeeds <i>and `f' is applicable
* to the result. If so, the result will be transformed by `f'.
*/
def ^? [U](f: PartialFunction[T, U]): Parser[U] = ^?(f, r => "Constructor function not defined at "+r)
/** A parser combinator that parameterizes a subsequent parser with the result of this one
*
*<p>
* Use this combinator when a parser depends on the result of a previous parser. `p' should be
* a function that takes the result from the first parser and returns the second parser.</p>
*
*<p> `p into fq' (with `fq' typically `{x => q}') first applies `p', and then, if `p' successfully
* returned result `r', applies `fq(r)' to the rest of the input. </p>
*
*<p> From: G. Hutton. Higher-order functions for parsing. J. Funct. Program., 2(3):323--343, 1992.
*
* @param fq a function that, given the result from this parser, returns the second parser to be applied
* @return a parser that succeeds if this parser succeeds (with result `x') and if then `fq(x)' succeeds
*/
def into[U](fq: T => Parser[U]): Parser[U] = flatMap(fq)
// shortcuts for combinators:
/** Returns into(fq) */
def >>[U](fq: T => Parser[U])=into(fq)
/** Returns a parser that repeatedly parses what this parser parses
*
* @return rep(this)
*/
def * = rep(this)
/** Returns a parser that repeatedly parses what this parser parses, interleaved with the `sep' parser.
* The `sep' parser specifies how the results parsed by this parser should be combined.
*
* @return chainl1(this, sep)
*/
def *[U >: T](sep: => Parser[(U, U) => U]) = chainl1(this, sep)
// TODO: improve precedence? a ~ b*(",") = a ~ (b*(",")) should be true
/** Returns a parser that repeatedly (at least once) parses what this parser parses.
*
* @return rep1(this)
*/
def + = rep1(this)
/** Returns a parser that optionally parses what this parser parses.
*
* @return opt(this)
*/
def ? = opt(this)
}
/** Wrap a parser so that its failures become errors (the | combinator will give up as soon as
* it encounters an error, on failure it simply tries the next alternative)
*/
def commit[T](p: => Parser[T]) = Parser{ in =>
p(in) match{
case s @ Success(_, _) => s
case e @ Error(_, _) => e
case f @ Failure(msg, next) => Error(msg, next)
}
}
/*trait ElemFun
case class EFCons(hd: Elem => ElemFun, tl: ElemFun) extends ElemFun
case class EFNil(res: Boolean) extends ElemFun*/
/** A parser matching input elements that satisfy a given predicate
*
* <p>elem(kind, p) succeeds if the input starts with an element `e' for which p(e) is true.
*
* @param kind The element kind, used for error messages
* @param p A predicate that determines which elements match.
* @return
*/
def elem(kind: String, p: Elem => Boolean) = acceptIf(p)(inEl => kind+" expected")
/** A parser that matches only the given element `e'
*
* <p>elem(e) succeeds if the input starts with an element `e'
*
* @param e the `Elem' that must be the next piece of input for the returned parser to succeed
* @return a `Parser' that succeeds if `e' is the next available input (and returns it).
*/
def elem(e: Elem): Parser[Elem] = accept(e)
/** A parser that matches only the given element `e'
*<p>
* The method is implicit so that elements can automatically be lifted to their parsers.
* For example, when parsing `Token's, Identifier("new") (which is a `Token') can be used directly,
* instead of first creating a `Parser' using accept(Identifier("new")).</p>
*
* @param e the `Elem' that must be the next piece of input for the returned parser to succeed
* @return a `tParser' that succeeds if `e' is the next available input.
*/
implicit def accept(e: Elem): Parser[Elem] = acceptIf(_ == e)("`"+e+"' expected but " + _ + " found")
/** A parser that matches only the given list of element `es'
*
* <p>accept(es) succeeds if the input subsequently provides the elements in the list `es'.
*
* @param es the list of expected elements
* @return a Parser that recognizes a specified list of elements
*/
def accept[ES <% List[Elem]](es: ES): Parser[List[Elem]] = acceptSeq(es)
/** The parser that matches an element in the domain of the partial function `f'
*<p>
* If `f' is defined on the first element in the input, `f' is applied to it to produce
* this parser's result.</p>
*<p>
* Example: The parser <code>accept("name", {case Identifier(n) => Name(n)})
* accepts an <code>Identifier(n) and returns a Name(n).
*
* @param expected a description of the kind of element this parser expects (for error messages)
* @param f a partial function that determines when this parser is successful and what its output is
* @return A parser that succeeds if `f' is applicable to the first element of the input,
* applying `f' to it to produce the result.
*/
def accept[U](expected: String, f: PartialFunction[Elem, U]): Parser[U] = acceptMatch(expected, f)
def acceptIf(p: Elem => Boolean)(err: Elem => String): Parser[Elem] = Parser { in =>
if (p(in.first)) Success(in.first, in.rest)
else Failure(err(in.first), in)
}
def acceptMatch[U](expected: String, f: PartialFunction[Elem, U]): Parser[U] = Parser{ in =>
if (f.isDefinedAt(in.first)) Success(f(in.first), in.rest)
else Failure(expected+" expected", in)
}
def acceptSeq[ES <% Iterable[Elem]](es: ES): Parser[List[Elem]] = es.foldRight[Parser[List[Elem]]](success(Nil)){(x, pxs) => accept(x) ~ pxs ^^ mkList}
/** A parser that always fails
*
* @param msg The error message describing the failure.
* @return A parser that always fails with the specified error message.
*/
def failure(msg: String) = Parser{ in => Failure(msg, in) }
/** A parser that results in an error
*
* @param msg The error message describing the failure.
* @return A parser that always fails with the specified error message.
*/
def err(msg: String) = Parser{ in => Error(msg, in) }
/** A parser that always succeeds
*
* @param v The result for the parser
* @return A parser that always succeeds, with the given result `v'
*/
def success[T](v: T) = Parser{ in => Success(v, in) }
def log[T](p: => Parser[T])(name: String): Parser[T] = Parser{ in =>
println("trying "+ name +" at "+ in)
val r = p(in)
println(name +" --> "+ r)
r
}
/** A parser generator for repetitions.
*
* <p> rep(p) repeatedly uses `p' to parse the input until `p' fails (the result is a List
* of the consecutive results of `p') </p>
*
* @param p a `Parser' that is to be applied successively to the input
* @return A parser that returns a list of results produced by repeatedly applying `p' to the input.
*/
def rep[T](p: => Parser[T]): Parser[List[T]] = rep1(p) | success(List())
/** A parser generator for interleaved repetitions.
*
* <p> repsep(p, q) repeatedly uses `p' interleaved with `q' to parse the input, until `p' fails.
* (The result is a `List' of the results of `p'.) </p>
*
* <p>Example: repsep(term, ",") parses a comma-separated list of term's,
* yielding a list of these terms</p>
*
* @param p a `Parser' that is to be applied successively to the input
* @param q a `Parser' that parses the elements that separate the elements parsed by `p'
* @return A parser that returns a list of results produced by repeatedly applying `p' (interleaved
* with `q') to the input.
* The results of `p' are collected in a list. The results of `q' are discarded.
*/
def repsep[T](p: => Parser[T], q: => Parser[Any]): Parser[List[T]] =
rep1sep(p, q) | success(List())
/** A parser generator for non-empty repetitions.
*
* <p> rep1(p) repeatedly uses `p' to parse the input until `p' fails -- `p' must succeed at least
* once (the result is a `List' of the consecutive results of `p')</p>
*
* @param p a `Parser' that is to be applied successively to the input
* @return A parser that returns a list of results produced by repeatedly applying `p' to the input
* (and that only succeeds if `p' matches at least once).
*/
def rep1[T](p: => Parser[T]): Parser[List[T]] = rep1(p, p)
/** A parser generator for non-empty repetitions.
*
* <p> rep1(f, p) first uses `f' (which must succeed) and then repeatedly uses `p' to
* parse the input until `p' fails
* (the result is a `List' of the consecutive results of `f' and `p')</p>
*
* @param first a `Parser' that parses the first piece of input
* @param p0 a `Parser' that is to be applied successively to the rest of the input (if any) -- evaluated at most once, and only when necessary
* @return A parser that returns a list of results produced by first applying `f' and then
* repeatedly `p' to the input (it only succeeds if `f' matches).
*/
@migration(2, 9, "As of 2.9, the p0 call-by-name arguments is evaluated at most once per constructed Parser object, instead of on every need that arises during parsing.")
def rep1[T](first: => Parser[T], p0: => Parser[T]): Parser[List[T]] = Parser { in =>
lazy val p = p0 // lazy argument
val elems = new ListBuffer[T]
def continue(in: Input): ParseResult[List[T]] = {
val p0 = p // avoid repeatedly re-evaluating by-name parser
@tailrec def applyp(in0: Input): ParseResult[List[T]] = p0(in0) match {
case Success(x, rest) => elems += x ; applyp(rest)
case _ => Success(elems.toList, in0)
}
applyp(in)
}
first(in) match {
case Success(x, rest) => elems += x ; continue(rest)
case ns: NoSuccess => ns
}
}
/** A parser generator for a specified number of repetitions.
*
* <p> repN(n, p) uses `p' exactly `n' time to parse the input
* (the result is a `List' of the `n' consecutive results of `p')</p>
*
* @param p a `Parser' that is to be applied successively to the input
* @param n the exact number of times `p' must succeed
* @return A parser that returns a list of results produced by repeatedly applying `p' to the input
* (and that only succeeds if `p' matches exactly `n' times).
*/
def repN[T](num: Int, p: => Parser[T]): Parser[List[T]] =
if (num == 0) success(Nil) else Parser { in =>
val elems = new ListBuffer[T]
val p0 = p // avoid repeatedly re-evaluating by-name parser
@tailrec def applyp(in0: Input): ParseResult[List[T]] =
if (elems.length == num) Success(elems.toList, in0)
else p0(in0) match {
case Success(x, rest) => elems += x ; applyp(rest)
case ns: NoSuccess => return ns
}
applyp(in)
}
/** A parser generator for non-empty repetitions.
*
* <p>rep1sep(p, q) repeatedly applies `p' interleaved with `q' to parse the input, until `p' fails.
* The parser `p' must succeed at least once.</p>
*
* @param p a `Parser' that is to be applied successively to the input
* @param q a `Parser' that parses the elements that separate the elements parsed by `p'
* (interleaved with `q')
* @return A parser that returns a list of results produced by repeatedly applying `p' to the input
* (and that only succeeds if `p' matches at least once).
* The results of `p' are collected in a list. The results of `q' are discarded.
*/
def rep1sep[T](p : => Parser[T], q : => Parser[Any]): Parser[List[T]] =
p ~ rep(q ~> p) ^^ {case x~y => x::y}
/** A parser generator that, roughly, generalises the rep1sep generator so that `q', which parses the separator,
* produces a left-associative function that combines the elements it separates.
*
* <p> From: J. Fokker. Functional parsers. In J. Jeuring and E. Meijer, editors, Advanced Functional Programming, volume 925 of Lecture Notes in Computer Science, pages 1--23. Springer, 1995.
*
* @param p a parser that parses the elements
* @param q a parser that parses the token(s) separating the elements, yielding a left-associative function that
* combines two elements into one
*/
def chainl1[T](p: => Parser[T], q: => Parser[(T, T) => T]): Parser[T]
= chainl1(p, p, q)
/** A parser generator that, roughly, generalises the rep1sep generator so that `q', which parses the separator,
* produces a left-associative function that combines the elements it separates.
*
* @param first a parser that parses the first element
* @param p a parser that parses the subsequent elements
* @param q a parser that parses the token(s) separating the elements, yielding a left-associative function that
* combines two elements into one
*/
def chainl1[T, U](first: => Parser[T], p: => Parser[U], q: => Parser[(T, U) => T]): Parser[T]
= first ~ rep(q ~ p) ^^ {
case x ~ xs => xs.foldLeft(x){(_, _) match {case (a, f ~ b) => f(a, b)}}
}
/** A parser generator that generalises the rep1sep generator so that `q', which parses the separator,
* produces a right-associative function that combines the elements it separates. Additionally,
* The right-most (last) element and the left-most combining function have to be supplied.
*
* rep1sep(p: Parser[T], q) corresponds to chainr1(p, q ^^ cons, cons, Nil) (where val cons = (x: T, y: List[T]) => x :: y)
*
* @param p a parser that parses the elements
* @param q a parser that parses the token(s) separating the elements, yielding a right-associative function that
* combines two elements into one
* @param combine the "last" (left-most) combination function to be applied
* @param first the "first" (right-most) element to be combined
*/
def chainr1[T, U](p: => Parser[T], q: => Parser[(T, U) => U], combine: (T, U) => U, first: U): Parser[U]
= p ~ rep(q ~ p) ^^ {
case x ~ xs => (new ~(combine, x) :: xs).
foldRight(first){(_, _) match {case (f ~ a, b) => f(a, b)}}
}
/** A parser generator for optional sub-phrases.
*
* <p>opt(p) is a parser that returns `Some(x)' if `p' returns `x' and `None' if `p' fails
*
* @param p A `Parser' that is tried on the input
* @return a `Parser' that always succeeds: either with the result provided by `p' or
* with the empty result
*/
def opt[T](p: => Parser[T]): Parser[Option[T]] =
p ^^ (x => Some(x)) | success(None)
/** Wrap a parser so that its failures&errors become success and vice versa -- it never consumes any input
*/
def not[T](p: => Parser[T]): Parser[Unit] = Parser { in =>
p(in) match {
case Success(_, _) => Failure("Expected failure", in)
case _ => Success((), in)
}
}
/** A parser generator for guard expressions. The resulting parser will fail or succeed
* just like the one given as parameter but it will not consume any input.
*
* @param p a `Parser' that is to be applied to the input
* @return A parser that returns success if and only if 'p' succeeds but never consumes any input
*/
def guard[T](p: => Parser[T]): Parser[T] = Parser { in =>
p(in) match{
case s@ Success(s1,_) => Success(s1, in)
case e => e
}
}
/** `positioned' decorates a parser's result with the start position of the input it consumed.
*
* @param p a `Parser' whose result conforms to `Positional'.
* @return A parser that has the same behaviour as `p', but which marks its result with the
* start position of the input it consumed, if it didn't already have a position.
*/
def positioned[T <: Positional](p: => Parser[T]): Parser[T] = Parser { in =>
p(in) match {
case Success(t, in1) => Success(if (t.pos == NoPosition) t setPos in.pos else t, in1)
case ns: NoSuccess => ns
}
}
/** <p>
* A parser generator delimiting whole phrases (i.e. programs).
* </p>
* <p>
* <code>phrase(p) succeeds if p succeeds and
* no input is left over after <code>p.
* </p>
*
* @param p the parser that must consume all input for the resulting parser
* to succeed.
* @return a parser that has the same result as `p', but that only succeeds
* if <code>p consumed all the input.
*/
def phrase[T](p: Parser[T]) = new Parser[T] {
lastNoSuccess = null
def apply(in: Input) = p(in) match {
case s @ Success(out, in1) =>
if (in1.atEnd)
s
else if (lastNoSuccess == null || lastNoSuccess.next.pos < in1.pos)
Failure("end of input expected", in1)
else
lastNoSuccess
case _ => lastNoSuccess
}
}
def mkList[T] = (_: ~[T, List[T]]) match { case x ~ xs => x :: xs }
case class ~[+a, +b](_1: a, _2: b) {
override def toString = "("+ _1 +"~"+ _2 +")"
}
/** A parser whose ~ combinator disallows back-tracking.
*/
trait OnceParser[+T] extends Parser[T] {
override def ~ [U](p: => Parser[U]): Parser[~[T, U]]
= OnceParser{ (for(a <- this; b <- commit(p)) yield new ~(a,b)).named("~") }
}
}
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