Class: Dendroid::Syntax::Rule

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

Overview

A specialization of the Rule class. A choice is a rule with multiple rhs

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(theLhs, alt) ⇒ Rule

Create a Rule instance.

Parameters:



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# File 'lib/dendroid/syntax/rule.rb', line 18

def initialize(theLhs, alt)
  @head = valid_head(theLhs)
  @alternatives = valid_alternatives(alt)
end

Instance Attribute Details

#alternatives ⇒ Array<Dendroid::Syntax::SymbolSeq> (readonly)

Returns:



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# File 'lib/dendroid/syntax/rule.rb', line 13

def alternatives
  @alternatives
end

#head ⇒ Dendroid::Syntax::NonTerminal (readonly) Also known as: lhs

Returns The left-hand side of the rule.

Returns:



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# File 'lib/dendroid/syntax/rule.rb', line 9

def head
  @head
end

Instance Method Details

#==(other) ⇒ Boolean

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

Returns:

  • (Boolean) 


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

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

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

#empty? ⇒ Boolean

Predicate method to check whether the rule has at least one empty alternative.

Returns:

  • (Boolean) 


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# File 'lib/dendroid/syntax/rule.rb', line 42

def empty?
  alternatives.any?(&:empty?)
end

#nonterminals ⇒ Array<Dendroid::Syntax::NonTerminal>

The set of all non-terminal symbols that occur in the rhs.

Returns:



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# File 'lib/dendroid/syntax/rule.rb', line 72

def nonterminals
  rhs_symbols.reject(&:terminal?)
end

#productive? ⇒ Boolean

Predicate method to check whether the choice rule body is productive. It is productive when at least one of its alternative is productive.

Returns:

  • (Boolean) 


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# File 'lib/dendroid/syntax/rule.rb', line 32

def productive?
  productive_alts = alternatives.select(&:productive?)
  return false if productive_alts.empty?

  @productive = Set.new(productive_alts)
  head.productive = true
end

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

Returns an array with the symbol sequence of its alternatives

Returns:



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# File 'lib/dendroid/syntax/rule.rb', line 48

def rhs
  alternatives
end

#rhs_symbols ⇒ Array<Dendroid::Syntax::GrmSymbol>

The set of all grammar symbols that occur in the rhs.

Returns:



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# File 'lib/dendroid/syntax/rule.rb', line 63

def rhs_symbols
  symbols = rhs.reduce([]) do |result, alt|
    result.concat(alt.members)
  end
  symbols.uniq
end

#terminals ⇒ Array<Dendroid::Syntax::Terminal>

The set of all terminal symbols that occur in the rhs.

Returns:



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# File 'lib/dendroid/syntax/rule.rb', line 78

def terminals
  rhs_symbols.select(&:terminal?)
end

#to_s ⇒ String

Return the text representation of the choice

Returns:

  • (String) 


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# File 'lib/dendroid/syntax/rule.rb', line 25

def to_s
  "#{head} => #{alternatives.join(' | ')}"
end