Class: EBNFLL1Parser

Inherits:
Object
  • Object
show all
Includes:
EBNF::LL1::Parser, EBNF::Terminals, EBNFParserMeta
Defined in:
examples/ebnf-ll1-parser/parser.rb

Defined Under Namespace

Classes: ProdResult

Constant Summary

Constants included from EBNF::Terminals

EBNF::Terminals::CHAR, EBNF::Terminals::HEX, EBNF::Terminals::LHS, EBNF::Terminals::O_RANGE, EBNF::Terminals::PASS, EBNF::Terminals::POSTFIX, EBNF::Terminals::RANGE, EBNF::Terminals::RANGE_NOT_LHS, EBNF::Terminals::R_CHAR, EBNF::Terminals::STRING1, EBNF::Terminals::STRING2, EBNF::Terminals::SYMBOL, EBNF::Terminals::SYMBOL_BASE

Constants included from EBNFParserMeta

EBNFParserMeta::BRANCH, EBNFParserMeta::CLEANUP, EBNFParserMeta::FIRST, EBNFParserMeta::FOLLOW, EBNFParserMeta::PASS, EBNFParserMeta::START, EBNFParserMeta::TERMINALS

Instance Attribute Summary collapse

Attributes included from EBNF::LL1::Parser

#lineno

Instance Method Summary collapse

Methods included from EBNF::LL1::Parser

#add_prod_data, #add_prod_datum, #debug, #depth, #error, #parse, #prod_data, #progress, #warn

Constructor Details

#initialize(input, **options, &block) ⇒ self

Parser invocation.

On start, yield ourselves if a block is given, otherwise, return this parser instance

Parameters:

  • input (#read, #to_s)
  • options (Hash{Symbol => Object})

Options Hash (**options):

  • :level (Boolean) —

    Trace level. 0(debug), 1(info), 2(warn), 3(error).



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# File 'examples/ebnf-ll1-parser/parser.rb', line 274

def initialize(input, **options, &block)
  # Read input, if necessary, which will be used in a Scanner which feads the Lexer.
  @input = input.respond_to?(:read) ? input.read : input.to_s

  # If the `level` option is set, instantiate a logger for collecting trace information.
  if options.key?(:level)
    options[:logger] ||= Logger.new(STDERR).
      tap {|x| x.level = options[:level]}.
      tap {|x| x.formatter = lambda {|severity, datetime, progname, msg| "#{severity} #{msg}\n"}}
  end

  parsing_terminals = false
  @ast = []
  parse(@input, START.to_sym, branch: BRANCH,
                              first: FIRST,
                              follow: FOLLOW,
                              cleanup: CLEANUP,
                              whitespace: EBNF::Terminals::PASS,
                              reset_on_start: true,
                              **options
  ) do |context, *data|
    rule = case context
    when :terminals
      # After parsing `@terminals`
      # This changes the state of the parser to treat subsequent rules as terminals.
      parsing_terminals = true
      rule = EBNF::Rule.new(nil, nil, data.first, kind: :terminals)
    when :pass
      # After parsing `@pass`
      # This defines a specific rule for whitespace.
      rule = EBNF::Rule.new(nil, nil, data.first, kind: :pass)
    when :rule
      # A rule which has already been turned into a `Rule` object.
      rule = data.first
      rule.kind = :terminal if parsing_terminals
      rule
    end
    @ast << rule if rule
  end
  @ast
end

Instance Attribute Details

#ast ⇒ Array<EBNF::Rule> (readonly)

Abstract syntax tree from parse

Returns:



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# File 'examples/ebnf-ll1-parser/parser.rb', line 37

def ast
  @ast
end

Instance Method Details

#to_sxp(**options) ⇒ String

Output formatted S-Expression of grammar

Returns:

  • (String) 


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# File 'examples/ebnf-ll1-parser/parser.rb', line 319

def to_sxp(**options)
  require 'sxp' unless defined?(SXP)
  # Output rules as a formatted S-Expression
  SXP::Generator.string(@ast.map(&:for_sxp))
end