Class: Dendroid::Syntax::Production

Inherits:
Rule
  • Object
show all
Defined in:
lib/dendroid/syntax/production.rb

Overview

A specialization of the Rule class. A production is a rule with a single rhs

Instance Attribute Summary collapse

Attributes inherited from Rule

#head

Instance Method Summary collapse

Methods inherited from Rule

#nonterminals, #rhs_symbols, #terminals

Constructor Details

#initialize(lhs, rhs) ⇒ Production

Create a Production instance.



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# File 'lib/dendroid/syntax/production.rb', line 16

def initialize(lhs, rhs)
  super(lhs)
  @body = valid_body(rhs)
end

Instance Attribute Details

#body ⇒ Dendroid::Syntax::SymbolSeq (readonly) 



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# File 'lib/dendroid/syntax/production.rb', line 11

def body
  @body
end

Instance Method Details

#==(other) ⇒ Boolean

Equality operator Two production rules are equal when their head and rhs are equal.



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# File 'lib/dendroid/syntax/production.rb', line 62

def ==(other)
  return true if equal?(other)

  (head == other.head) && (body == other.body)
end

#choice? ⇒ FalseClass

Predicate method to check whether the rule has alternatives



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# File 'lib/dendroid/syntax/production.rb', line 29

def choice?
  false
end

#empty? ⇒ Boolean

Predicate method to check whether the rule body (its rhs) is empty.



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# File 'lib/dendroid/syntax/production.rb', line 23

def empty?
  body.empty?
end

#non_productive ⇒ Object

Mark the production rule as non-productive.



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# File 'lib/dendroid/syntax/production.rb', line 49

def non_productive
  self.productive = false
end

#productive? ⇒ Boolean, NilClass

Predicate method to check whether the production rule body is productive. It is productive when it is empty or all of its rhs members are productive too.



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# File 'lib/dendroid/syntax/production.rb', line 36

def productive?
  if @productive.nil?
    if body.productive?
      self.productive = true
    else
      nil
    end
  else
    @productive
  end
end

#rhs ⇒ Array<Dendroid::Syntax::SymbolSeq>

Returns an array with the symbol sequence of its rhs



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# File 'lib/dendroid/syntax/production.rb', line 70

def rhs
  [body]
end

#to_s ⇒ String

Return the text representation of the production rule



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# File 'lib/dendroid/syntax/production.rb', line 55

def to_s
  "#{head} => #{body}"
end