91 lines
2.6 KiB
Ruby
91 lines
2.6 KiB
Ruby
module Parslet::Atoms
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# Helper class that implements a transient cache that maps position and
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# parslet object to results. This is used for memoization in the packrat
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# style.
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#
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# Also, error reporter is stored here and error reporting happens through
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# this class. This makes the reporting pluggable.
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#
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class Context
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# @param reporter [#err, #err_at] Error reporter (leave empty for default
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# reporter)
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def initialize(reporter=Parslet::ErrorReporter::Tree.new)
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@cache = Hash.new { |h, k| h[k] = {} }
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@reporter = reporter
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@captures = Parslet::Scope.new
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end
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# Caches a parse answer for obj at source.pos. Applying the same parslet
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# at one position of input always yields the same result, unless the input
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# has changed.
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#
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# We need the entire source here so we can ask for how many characters
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# were consumed by a successful parse. Imitation of such a parse must
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# advance the input pos by the same amount of bytes.
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#
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def try_with_cache(obj, source, consume_all)
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beg = source.pos
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# Not in cache yet? Return early.
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unless entry = lookup(obj, beg)
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result = obj.try(source, self, consume_all)
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if obj.cached?
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set obj, beg, [result, source.pos-beg]
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end
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return result
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end
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# the condition in unless has returned true, so entry is not nil.
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result, advance = entry
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# The data we're skipping here has been read before. (since it is in
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# the cache) PLUS the actual contents are not interesting anymore since
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# we know obj matches at beg. So skip reading.
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source.pos = beg + advance
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return result
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end
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# Report an error at a given position.
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# @see ErrorReporter
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#
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def err_at(*args)
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return [false, @reporter.err_at(*args)] if @reporter
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return [false, nil]
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end
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# Report an error.
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# @see ErrorReporter
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#
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def err(*args)
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return [false, @reporter.err(*args)] if @reporter
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return [false, nil]
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end
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# Returns the current captures made on the input (see
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# Parslet::Atoms::Base#capture). Use as follows:
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#
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# context.captures[:foobar] # => returns capture :foobar
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#
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attr_reader :captures
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# Starts a new scope. Use the #scope method of Parslet::Atoms::DSL
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# to call this.
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#
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def scope
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captures.push
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yield
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ensure
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captures.pop
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end
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private
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def lookup(obj, pos)
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@cache[pos][obj]
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end
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def set(obj, pos, val)
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@cache[pos][obj] = val
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end
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end
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end |