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Object

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Parslet::Atoms::Context

Helper class that implements a transient cache that maps position and parslet object to results. This is used for memoization in the packrat style.

Also, error reporter is stored here and error reporting happens through this class. This makes the reporting pluggable.

Public Class Methods

new(reporter=Parslet::ErrorReporter::Tree.new) click to toggle source

@param reporter [err, err_at] Error reporter (leave empty for default

reporter)
# File lib/parslet/atoms/context.rb, line 12
def initialize(reporter=Parslet::ErrorReporter::Tree.new)
  @cache = Hash.new { |h, k| h[k] = {} }
  @reporter = reporter
end

Public Instance Methods

err(*args) click to toggle source

Report an error. @see ErrorReporter

# File lib/parslet/atoms/context.rb, line 57
def err(*args)
  return [false, @reporter.err(*args)] if @reporter
  return [false, nil]
end
err_at(*args) click to toggle source

Report an error at a given position. @see ErrorReporter

# File lib/parslet/atoms/context.rb, line 49
def err_at(*args)
  return [false, @reporter.err_at(*args)] if @reporter
  return [false, nil]
end
try_with_cache(obj, source) click to toggle source

Caches a parse answer for obj at source.pos. Applying the same parslet at one position of input always yields the same result, unless the input has changed.

We need the entire source here so we can ask for how many characters were consumed by a successful parse. Imitation of such a parse must advance the input pos by the same amount of bytes.

# File lib/parslet/atoms/context.rb, line 25
def try_with_cache(obj, source)
  beg = source.pos
    
  # Not in cache yet? Return early.
  unless entry = lookup(obj, beg)
    result = obj.try(source, self)

    set obj, beg, [result, source.pos-beg]
    return result
  end

  # the condition in unless has returned true, so entry is not nil.
  result, advance = entry

  # The data we're skipping here has been read before. (since it is in 
  # the cache) PLUS the actual contents are not interesting anymore since
  # we know obj matches at beg. So skip reading.
  source.pos = beg + advance
  return result
end

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