Method: RLTK::Parser.clause

Defined in:
lib/rltk/parser.rb

.clause(expression, precedence = nil, &action) ⇒ void Also known as: c

This method returns an undefined value.

Declares a new clause inside of a production. The right-hand side is specified by expression and the precedence of this production can be changed by setting the precedence argument to some terminal symbol.

Parameters:

  • expression (String) —

    Right-hand side of a production.

  • precedence (Symbol) (defaults to: nil) —

    Symbol representing the precedence of this production.

  • action (Proc) —

    Action to be taken when the production is reduced.



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# File 'lib/rltk/parser.rb', line 353

def clause(expression, precedence = nil, &action)
  # Use the curr_prec only if it isn't overridden for this
  # clause.
  precedence ||= @curr_prec
  
  production = @grammar.clause(expression)
  
  # Check to make sure the action's arity matches the number
  # of symbols on the right-hand side.
  if @args == :splat and action.arity != production.rhs.length
    raise ParserConstructionException, 'Incorrect number of arguments to action.  Action arity must match the number of ' +
      'terminals and non-terminals in the clause.'
  end
  
  # Add the action to our proc list.
  @procs[production.id] = [action, production.rhs.length]
  
  # If no precedence is specified use the precedence of the
  # last terminal in the production.
  @production_precs[production.id] = precedence || production.last_terminal
end