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# This wraps pieces of parslet definition and gives them a name. The wrapped
# piece is lazily evaluated and cached. This has two purposes:
#
# * Avoid infinite recursion during evaluation of the definition
# * Be able to print things by their name, not by their sometimes
# complicated content.
#
# You don't normally use this directly, instead you should generated it by
# using the structuring method Parslet.rule.
#
class Parslet::Atoms::Entity < Parslet::Atoms::Base
attr_reader :name, :block
def initialize(name, &block)
super()
@name = name
@block = block
end
def try(source, context, consume_all)
parslet.apply(source, context, consume_all)
end
def parslet
@parslet ||= @block.call.tap { |p|
raise_not_implemented unless p
}
end
def to_s_inner(prec)
name.to_s.upcase
end
private
def raise_not_implemented
trace = caller.reject {|l| l =~ %r{#{Regexp.escape(__FILE__)}}} # blatantly stolen from dependencies.rb in activesupport
exception = NotImplementedError.new("rule(#{name.inspect}) { ... } returns nil. Still not implemented, but already used?")
exception.set_backtrace(trace)
raise exception
end
end
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