Packages

  • package root
    Definition Classes
    root
  • package scala
    Definition Classes
    root
  • package util
    Definition Classes
    scala
  • package parsing
    Definition Classes
    util
  • package combinator
    Definition Classes
    parsing
  • trait PackratParsers extends Parsers

    PackratParsers is a component that extends the parser combinators provided by scala.util.parsing.combinator.Parsers with a memoization facility (Packrat Parsing).

    PackratParsers is a component that extends the parser combinators provided by scala.util.parsing.combinator.Parsers with a memoization facility (Packrat Parsing).

    Packrat Parsing is a technique for implementing backtracking, recursive-descent parsers, with the advantage that it guarantees unlimited lookahead and a linear parse time. Using this technique, left recursive grammars can also be accepted.

    Using PackratParsers is very similar to using Parsers:

    • any class/trait that extends Parsers (directly or through a subclass) can mix in PackratParsers. Example: object MyGrammar extends StandardTokenParsers with PackratParsers
    • each grammar production previously declared as a def without formal parameters becomes a lazy val, and its type is changed from Parser[Elem] to PackratParser[Elem]. So, for example, def production: Parser[Int] = {...} becomes lazy val production: PackratParser[Int] = {...}
    • Important: using PackratParsers is not an all or nothing decision. They can be free mixed with regular Parsers in a single grammar.

    Cached parse results are attached to the input, not the grammar. Therefore, PackratsParsers require a PackratReader as input, which adds memoization to an underlying Reader. Programmers can create PackratReader objects either manually, as in production(new PackratReader(new lexical.Scanner("input"))), but the common way should be to rely on the combinator phrase to wrap a given input with a PackratReader if the input is not one itself.

    Definition Classes
    combinator
    Since

    2.8

    See also

    Alessandro Warth, James R. Douglass, Todd Millstein: "Packrat Parsers Can Support Left Recursion." PEPM'08

    Bryan Ford: "Packrat Parsing: Simple, Powerful, Lazy, Linear Time." ICFP'02

  • Elem
  • Error
  • Failure
  • NoSuccess
  • OnceParser
  • PackratParser
  • PackratReader
  • ParseResult
  • Parser
  • Success
  • ~

class PackratReader[+T] extends Reader[T]

A specialized Reader class that wraps an underlying Reader and provides memoization of parse results.

Self Type
PackratReader[T]
Source
PackratParsers.scala
Linear Supertypes
Reader[T], AnyRef, Any
Ordering
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Inherited
  1. PackratReader
  2. Reader
  3. AnyRef
  4. Any
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Visibility
  1. Public
  2. All

Instance Constructors

  1. new PackratReader(underlying: Reader[T])

Value Members

  1. def atEnd: Boolean

    true iff there are no more elements in this reader.

    true iff there are no more elements in this reader.

    Definition Classes
    PackratReader → Reader
  2. def drop(n: Int): Reader[T]

    Returns an abstract reader consisting of all elements except the first n elements.

    Returns an abstract reader consisting of all elements except the first n elements.

    Definition Classes
    Reader
  3. def first: T

    Returns the first element of the reader

    Returns the first element of the reader

    Definition Classes
    PackratReader → Reader
  4. def offset: Int
    Definition Classes
    PackratReader → Reader
  5. def pos: Position

    The position of the first element in the reader.

    The position of the first element in the reader.

    Definition Classes
    PackratReader → Reader
  6. def rest: Reader[T]

    Returns an abstract reader consisting of all elements except the first

    Returns an abstract reader consisting of all elements except the first

    returns

    If atEnd is true, the result will be this'; otherwise, it's a Reader containing more elements.

    Definition Classes
    PackratReader → Reader
  7. def source: CharSequence

    If this is a reader over character sequences, the underlying char sequence.

    If this is a reader over character sequences, the underlying char sequence. If not, throws a NoSuchMethodError exception.

    Definition Classes
    PackratReader → Reader
    Exceptions thrown

    [[java.lang.NoSuchMethodError]] if this not a char sequence reader.