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require_relative 'symbol_seq'
module Rley # This module is used as a namespace
module Syntax # This module is used as a namespace
# In a context-free grammar, a production is a rule in which
# its left-hand side (LHS) consists solely of a non-terminal symbol
# and the right-hand side (RHS) consists of a sequence of symbols.
# The symbols in RHS can be either terminal or non-terminal symbols.
# The rule stipulates that the LHS is equivalent to the RHS,
# in other words every occurrence of the LHS can be substituted to
# corresponding RHS.
class Production
# The right-hand side (rhs) consists of a sequence of grammar symbols
attr_reader(:rhs)
# The left-hand side of the rule. It must be a non-terminal symbol
attr_reader(:lhs)
# Provide common alternate names to lhs and rhs accessors
alias body rhs
alias head lhs
def initialize(aNonTerminal, theSymbols)
@lhs = valid_lhs(aNonTerminal)
@rhs = SymbolSeq.new(theSymbols)
end
# Is the rhs empty?
# @ return true if the rhs has no members.
def empty?()
return rhs.empty?
end
private
# Validation method. Return the validated input argument or
# raise an exception.
def valid_lhs(aNonTerminal)
unless aNonTerminal.kind_of?(NonTerminal)
msg_prefix = 'Left side of production must be a non-terminal symbol'
msg_suffix = ", found a #{aNonTerminal.class} instead."
raise StandardError, msg_prefix + msg_suffix
end
return aNonTerminal
end
end # class
end # module
end # module
# End of file
Version data entries
14 entries across 14 versions & 1 rubygems