Class: EBNF::Rule

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

Overview

Represent individual parsed rules

Constant Summary collapse

BNF_OPS =

Operations which are flattened to seprate rules in to_bnf

%w{
  alt opt plus seq star
}.map(&:to_sym).freeze
TERM_OPS = 
%w{
  diff hex range
}.map(&:to_sym).freeze

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(sym, id, expr, options = {}) ⇒ Rule

option options [Boolean] :start

Parameters:

  • id (Integer)
  • sym (Symbol)
  • expr (Array)
  • options (Hash{Symbol => Object}) (defaults to: {})

Options Hash (options):

  • :kind (Symbol)
  • :ebnf (String)
  • :first (Array)
  • :follow (Array) 


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# File 'lib/ebnf/rule.rb', line 66

def initialize(sym, id, expr, options = {})
  @sym, @id = sym, id
  @expr = expr.is_a?(Array) ? expr : [:seq, expr]
  @ebnf = options[:ebnf]
  @top_rule = options.fetch(:top_rule, self)
  @first = options[:first]
  @follow = options[:follow]
  @start = options[:start]
  @kind = case
  when options[:kind] then options[:kind]
  when sym.to_s == sym.to_s.upcase then :terminal
  when !BNF_OPS.include?(@expr.first) then :terminal
  else :rule
  end
end

Instance Attribute Details

#comp ⇒ Rule

A comprehension is a sequence which contains all elements but the first of the original rule.

Returns:



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# File 'lib/ebnf/rule.rb', line 25

def comp
  @comp
end

#expr ⇒ Array

Rule expression

Returns:

  • (Array) 


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# File 'lib/ebnf/rule.rb', line 35

def expr
  @expr
end

#first ⇒ Array<Rule> (readonly)

Terminals that immediately procede this rule

Returns:



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# File 'lib/ebnf/rule.rb', line 45

def first
  @first
end

#follow ⇒ Array<Rule> (readonly)

Terminals that immediately follow this rule

Returns:



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# File 'lib/ebnf/rule.rb', line 50

def follow
  @follow
end

#id ⇒ String

ID of rule

Returns:

  • (String) 


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# File 'lib/ebnf/rule.rb', line 20

def id
  @id
end

#kind ⇒ :rule, ...

Kind of rule

Returns:

  • (:rule, :terminal, or :pass) 


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# File 'lib/ebnf/rule.rb', line 30

def kind
  @kind
end

#orig ⇒ String

Original EBNF

Returns:

  • (String) 


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# File 'lib/ebnf/rule.rb', line 40

def orig
  @orig
end

#start ⇒ Boolean

Indicates that this is a starting rule

Returns:

  • (Boolean) 


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# File 'lib/ebnf/rule.rb', line 55

def start
  @start
end

#sym ⇒ Symbol

Symbol of rule

Returns:

  • (Symbol) 


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# File 'lib/ebnf/rule.rb', line 16

def sym
  @sym
end

Class Method Details

.from_sxp(sxp) ⇒ Rule

Return a rule from its SXP representation:

Also may have (first …), (follow …), or (start #t)

Examples:

inputs

(pass (plus (range "#x20\\t\\r\\n")))
(rule ebnf "1" (star (alt declaration rule)))
(terminal O_ENUM "17" (seq "[^" (plus CHAR) "]"))

Parameters:

  • sxp (Array)

Returns:



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# File 'lib/ebnf/rule.rb', line 94

def self.from_sxp(sxp)
  expr = sxp.detect {|e| e.is_a?(Array) && ![:first, :follow, :start].include?(e.first.to_sym)}
  first = sxp.detect {|e| e.is_a?(Array) && e.first.to_sym == :first}
  first = first[1..-1] if first
  follow = sxp.detect {|e| e.is_a?(Array) && e.first.to_sym == :follow}
  follow = follow[1..-1] if follow
  start = sxp.any? {|e| e.is_a?(Array) && e.first.to_sym == :start}
  sym = sxp[1] if sxp[1].is_a?(Symbol)
  id = sxp[2] if sxp[2].is_a?(String)
  Rule.new(sym, id, expr, :kind => sxp.first, :first => first, :follow => follow, :start => start)
end

Instance Method Details

#<=>(other) ⇒ Object

Rules compare using their ids



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# File 'lib/ebnf/rule.rb', line 379

def <=>(other)
  if id.to_i == other.id.to_i
    id <=> other.id
  else
    id.to_i <=> other.id.to_i
  end
end

#==(other) ⇒ Boolean

Two rules are equal if they have the same #sym, #kind and #expr

Parameters:

Returns:

  • (Boolean) 


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# File 'lib/ebnf/rule.rb', line 350

def ==(other)
  sym   == other.sym &&
  kind  == other.kind &&
  expr  == other.expr
end

#add_first(terminals) ⇒ Integer

Add terminal as proceding this rule

Parameters:

  • terminals (Array<Rule, Symbol, String>)

Returns:

  • (Integer) —

    if number of terminals added



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# File 'lib/ebnf/rule.rb', line 287

def add_first(terminals)
  @first ||= []
  terminals = terminals.map {|t| t.is_a?(Rule) ? t.sym : t} - @first
  @first += terminals
  terminals.length
end

#add_follow(terminals) ⇒ Integer

Add terminal as following this rule. Don’t add _eps as a follow

Parameters:

  • terminals (Array<Rule, Symbol, String>)

Returns:

  • (Integer) —

    if number of terminals added



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# File 'lib/ebnf/rule.rb', line 298

def add_follow(terminals)
  # Remove terminals already in follows, and empty string
  terminals = terminals.map {|t| t.is_a?(Rule) ? t.sym : t} - (@follow || []) - [:_eps]
  unless terminals.empty?
    @follow ||= []
    @follow += terminals
  end
  terminals.length
end

#alt? ⇒ Boolean

Is this rule of the form (alt …)?

Returns:

  • (Boolean) 


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# File 'lib/ebnf/rule.rb', line 327

def alt?
  expr.is_a?(Array) && expr.first == :alt
end

#build(expr, options = {}) ⇒ Object

Build a new rule creating a symbol and numbering from the current rule Symbol and number creation is handled by the top-most rule in such a chain

Parameters:

  • expr (Array)
  • options (Hash{Symbol => Object}) (defaults to: {})

Options Hash (options):

  • :kind (Symbol)
  • :ebnf (String) —

    EBNF instance (used for messages)



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# File 'lib/ebnf/rule.rb', line 113

def build(expr, options = {})
  new_sym, new_id = (@top_rule ||self).send(:make_sym_id)
  Rule.new(new_sym, new_id, expr, {
    :kind => options[:kind],
    :ebnf => @ebnf,
    :top_rule => @top_rule || self,
  }.merge(options))
end

#equivalent?(other) ⇒ Boolean

Two rules are equivalent if they have the same #expr

Parameters:

Returns:

  • (Boolean) 


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# File 'lib/ebnf/rule.rb', line 359

def equivalent?(other)
  expr  == other.expr
end

#first_includes_eps? ⇒ Boolean

Do the firsts of this rule include the empty string?

Returns:

  • (Boolean) 


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# File 'lib/ebnf/rule.rb', line 280

def first_includes_eps?
  @first && @first.include?(:_eps)
end

#for_sxp ⇒ Array

Return representation for building S-Expressions

Returns:

  • (Array) 


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# File 'lib/ebnf/rule.rb', line 124

def for_sxp
  elements = [kind, sym]
  elements << id if id
  elements << [:start, true] if start
  elements << first.sort_by(&:to_s).unshift(:first) if first
  elements << follow.sort_by(&:to_s).unshift(:follow) if follow
  elements << expr
  elements
end

#inspect ⇒ Object 



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# File 'lib/ebnf/rule.rb', line 341

def inspect
  "#<EBNF::Rule:#{object_id} " +
  {:sym => sym, :id => id, :kind => kind, :expr => expr}.inspect +
  ">"
end

#non_terminals(ast) ⇒ Array<Rule>

Return the non-terminals for this rule. For seq, this is the first non-terminals in the seq. For alt, this is every non-terminal ni the alt

Parameters:

  • ast (Array<Rule>) —

    The set of rules, used to turn symbols into rules

Returns:



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# File 'lib/ebnf/rule.rb', line 231

def non_terminals(ast)
  @non_terms ||= (alt? ? expr[1..-1] : expr[1,1]).map do |sym|
    case sym
    when Symbol
      r = ast.detect {|r| r.sym == sym}
      r if r && r.rule?
    else
      nil
    end
  end.compact
end

#pass? ⇒ Boolean

Is this a pass?

Returns:

  • (Boolean) 


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# File 'lib/ebnf/rule.rb', line 316

def pass?
  kind == :pass
end

#rewrite(src_rule, dst_rule) ⇒ Rule

Rewrite the rule substituting src_rule for dst_rule wherever it is used in the production (first level only).

Parameters:

Returns:



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# File 'lib/ebnf/rule.rb', line 368

def rewrite(src_rule, dst_rule)
  case @expr
  when Array
    @expr = @expr.map {|e| e == src_rule.sym ? dst_rule.sym : e}
  else
    @expr = dst_rule.sym if @expr == src_rule.sym
  end
  self
end

#rule? ⇒ Boolean

Is this a rule?

Returns:

  • (Boolean) 


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# File 'lib/ebnf/rule.rb', line 322

def rule?
  kind == :rule
end

#seq? ⇒ Boolean

Is this rule of the form (seq …)?

Returns:

  • (Boolean) 


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# File 'lib/ebnf/rule.rb', line 332

def seq?
  expr.is_a?(Array) && expr.first == :seq
end

#starts_with?(sym) ⇒ Array<Symbol, String>

Does this rule start with a sym? It does if expr is that sym, expr starts with alt and contains that sym, or expr starts with seq and the next element is that sym

Parameters:

  • sym (Symbol, class) —

    Symbol matching any start element, or if it is String, any start element which is a String

Returns:

  • (Array<Symbol, String>) —

    list of symbol (singular), or strings which are start symbol, or nil if there are none



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# File 'lib/ebnf/rule.rb', line 268

def starts_with?(sym)
  if seq? && sym === (v = expr.fetch(1, nil))
    [v]
  elsif alt? && expr.any? {|e| sym === e}
    expr.select {|e| sym === e}
  else
    nil
  end
end

#terminal? ⇒ Boolean

Is this a terminal?

Returns:

  • (Boolean) 


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# File 'lib/ebnf/rule.rb', line 310

def terminal?
  kind == :terminal
end

#terminals(ast) ⇒ Array<Rule>

Return the terminals for this rule. For seq, this is the first terminals or strings in the seq. For alt, this is every non-terminal ni the alt

Parameters:

  • ast (Array<Rule>) —

    The set of rules, used to turn symbols into rules

Returns:



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# File 'lib/ebnf/rule.rb', line 248

def terminals(ast)
  @terms ||= (alt? ? expr[1..-1] : expr[1,1]).map do |sym|
    case sym
    when Symbol
      r = ast.detect {|r| r.sym == sym}
      r if r && r.terminal?
    when String
      sym
    else
      nil
    end
  end.compact
end

#to_bnf ⇒ Array<Rule>

Transform EBNF rule to BNF rules:

* Transform (a [n] rule (op1 (op2))) into two rules:
  (a [n] rule (op1 _a_1))
  (_a_1 [n.1] rule (op2))
* Transform (a rule (opt b)) into (a rule (alt _empty b))
* Transform (a rule (star b)) into (a rule (alt _empty (seq b a)))
* Transform (a rule (plus b)) into (a rule (seq b (star b)

Transformation includes information used to re-construct non-transformed AST representation

Returns:



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# File 'lib/ebnf/rule.rb', line 173

def to_bnf
  return [self] unless rule?
  new_rules = []

  # Look for rules containing recursive definition and rewrite to multiple rules. If `expr` contains elements which are in array form, where the first element of that array is a symbol, create a new rule for it.
  if expr.any? {|e| e.is_a?(Array) && (BNF_OPS + TERM_OPS).include?(e.first)}
    #   * Transform (a [n] rule (op1 (op2))) into two rules:
    #     (a.1 [n.1] rule (op1 a.2))
    #     (a.2 [n.2] rule (op2))
    # duplicate ourselves for rewriting
    this = dup
    new_rules << this

    expr.each_with_index do |e, index|
      next unless e.is_a?(Array) && e.first.is_a?(Symbol)
      new_rule = build(e)
      this.expr[index] = new_rule.sym
      new_rules << new_rule
    end

    # Return new rules after recursively applying #to_bnf
    new_rules = new_rules.map {|r| r.to_bnf}.flatten
  elsif expr.first == :opt
    this = dup
    #   * Transform (a rule (opt b)) into (a rule (alt _empty b))
    this.expr = [:alt, :_empty, expr.last]
    new_rules = this.to_bnf
  elsif expr.first == :star
    #   * Transform (a rule (star b)) into (a rule (alt _empty (seq b a)))
    this = dup
    new_rule = this.build([:seq, expr.last, this.sym])
    this.expr = [:alt, :_empty, new_rule.sym]
    new_rules = [this] + new_rule.to_bnf
  elsif expr.first == :plus
    #   * Transform (a rule (plus b)) into (a rule (seq b (star b)
    this = dup
    this.expr = [:seq, expr.last, [:star, expr.last]]
    new_rules = this.to_bnf
  elsif [:alt, :seq].include?(expr.first)
    # Otherwise, no further transformation necessary
    new_rules << self
  elsif [:diff, :hex, :range].include?(expr.first)
    # This rules are fine, the just need to be terminals
    raise "Encountered #{expr.first.inspect}, which is a #{self.kind}, not :terminal" unless self.terminal?
    new_rules << self
  else
    # Some case we didn't think of
    raise "Error trying to transform #{expr.inspect} to BNF"
  end
  
  return new_rules
end

#to_sxp ⇒ String Also known as: to_s

Return SXP representation of this rule

Returns:

  • (String) 


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# File 'lib/ebnf/rule.rb', line 136

def to_sxp
  for_sxp.to_sxp
end

#to_ttl ⇒ String

Serializes this rule to an Turtle

Returns:

  • (String) 


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# File 'lib/ebnf/rule.rb', line 144

def to_ttl
  @ebnf.debug("to_ttl") {inspect}
  comment = orig.strip.
    gsub(/"""/, '\"\"\"').
    gsub("\\", "\\\\").
    sub(/^\"/, '\"').
    sub(/\"$/m, '\"')
  statements = [
    %{:#{id} rdfs:label "#{id}"; rdf:value "#{sym}";},
    %{  rdfs:comment #{comment.inspect};},
  ]
  
  statements += ttl_expr(expr, terminal? ? "re" : "g", 1, false)
  "\n" + statements.join("\n")
end