Class: Dendroid::Syntax::Grammar

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

Overview

A grammar specifies the syntax of a language.

Formally, a grammar has:
* One start symbol,
* One or more other production rules,
* Each production has a rhs that is a sequence of grammar symbols.
* Grammar symbols are categorized into:
  -terminal symbols
  -non-terminal symbols

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(terminals) ⇒ Grammar

Constructor.

Parameters:



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# File 'lib/dendroid/syntax/grammar.rb', line 34

def initialize(terminals)
  @symbols = []
  @name2symbol = {}
  @rules = []
  @nonterm2production = {}
  add_terminals(terminals)
end

Instance Attribute Details

#name2symbol ⇒ Hash{String|Symbol => Dendroid::Syntax::GrmSymbol} (readonly)

A Hash that maps symbol names to their grammar symbols

Returns:



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# File 'lib/dendroid/syntax/grammar.rb', line 22

def name2symbol
  @name2symbol
end

#nonterm2production ⇒ Hash{Dendroid::Syntax::GrmSymbol => Dendroid::Syntax::Rule} (readonly)

A Hash that maps symbol names to their grammar symbols

Returns:



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# File 'lib/dendroid/syntax/grammar.rb', line 30

def nonterm2production
  @nonterm2production
end

#rules ⇒ Array<Dendroid::Syntax::Rule> (readonly)

The list of production rules for the language.

Returns:



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# File 'lib/dendroid/syntax/grammar.rb', line 26

def rules
  @rules
end

#symbols ⇒ Array<Dendroid::Syntax::GrmSymbol> (readonly)

The list of grammar symbols in the language.

Returns:



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

def symbols
  @symbols
end

Instance Method Details

#add_rule(rule) ⇒ Object

Add a rule to the grammar.

Parameters:



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# File 'lib/dendroid/syntax/grammar.rb', line 46

def add_rule(rule)
  if lhs_already_defined?(rule)
    msg = "Non-terminal '#{rule.head}' is on left-hand side of more than one rule."
    raise StandardError, msg
  end
  if duplicate_rule?(rule)
    raise StandardError, "Duplicate production rule '#{rule}'."
  end

  add_symbol(rule.head)
  rule.nonterminals.each { |nonterm| add_symbol(nonterm) }
  rules << rule
  nonterm2production[rule.head] = rule
end

#complete! ⇒ Object

A event method to notify the grammar that all grammar rules have been entered. The grammar, in turn, reacts by validating the production rules.



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# File 'lib/dendroid/syntax/grammar.rb', line 73

def complete!
  validate
  analyze
end

#start_symbol ⇒ Dendroid::Syntax::NonTerminal

Return the start symbol for the language, that is, the non-terminal symbol used to denote the top-level construct of the language being defined.

Returns:



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# File 'lib/dendroid/syntax/grammar.rb', line 66

def start_symbol
  rules.first.lhs
end