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Contents
require_relative 'grm_symbol' # Load superclass
module Rley # This module is used as a namespace
module Syntax # This module is used as a namespace
# A non-terminal symbol (sometimes called a syntactic variable) represents
# a composition of terminal or non-terminal symbols
class NonTerminal < GrmSymbol
# A non-terminal symbol is nullable if it can match an empty string.
attr_writer(:nullable)
# A non-terminal symbol is undefined if no production rule in the grammar
# has that non-terminal symbol in its left-hand side.
attr_writer(:undefined)
# A non-terminal symbol is unreachable if it cannot be reached (derived)
# from the start symbol.
attr_writer(:unreachable)
# Constructor.
# @param aName [String] The name of the grammar symbol.
def initialize(aName)
super(aName)
end
# @return [false/true] Return true if the symbol derives
# the empty string. As non-terminal symbol is nullable when it can
# can match to zero input token.
# The "nullability" of a non-terminal can practically be determined once
# all the production rules of the grammar are specified.
def nullable?()
return @nullable
end
# @return [false/true] Return true if the symbol doesn't appear
# on the left-hand side of any production rule.
def undefined?()
return @undefined
end
# @return [false/true] Return true if the symbol cannot be derived
# from the start symbol.
def unreachable?()
return @unreachable
end
end # class
end # module
end # module
# End of file
Version data entries
32 entries across 32 versions & 1 rubygems