Class: EBNF::Rule
- Inherits:
-
Object
- Object
- EBNF::Rule
- 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
-
#comp ⇒ Rule
A comprehension is a sequence which contains all elements but the first of the original rule.
-
#expr ⇒ Array
Rule expression.
-
#first ⇒ Array<Rule>
readonly
Terminals that immediately procede this rule.
-
#follow ⇒ Array<Rule>
readonly
Terminals that immediately follow this rule.
-
#id ⇒ String
ID of rule.
-
#kind ⇒ :rule, ...
Kind of rule.
-
#orig ⇒ String
Original EBNF.
-
#start ⇒ Boolean
Indicates that this is a starting rule.
-
#sym ⇒ Symbol
Symbol of rule.
Instance Method Summary collapse
-
#<=>(other) ⇒ Object
Rules compare using their ids.
- #==(other) ⇒ Boolean
-
#add_first(terminals) ⇒ Integer
Add terminal as proceding this rule.
-
#add_follow(terminals) ⇒ Integer
Add terminal as following this rule.
-
#alt? ⇒ Boolean
Is this rule of the form (alt …)?.
-
#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.
-
#equivalent?(other) ⇒ Boolean
Two rules are equivalent if they have the same #expr.
-
#first_includes_eps? ⇒ Boolean
Do the firsts of this rule include the empty string?.
-
#for_sxp ⇒ Array
Return representation for building S-Expressions.
-
#initialize(sym, id, expr, options = {}) ⇒ Rule
constructor
A new instance of Rule.
- #inspect ⇒ Object
-
#non_terminals(ast) ⇒ Array<Rule>
Return the non-terminals for this rule.
-
#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).
-
#rule? ⇒ Boolean
Is this a rule?.
-
#seq? ⇒ Boolean
Is this rule of the form (seq …)?.
-
#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.
-
#terminal? ⇒ Boolean
Is this a terminal?.
-
#terminals(ast) ⇒ Array<Rule>
Return the terminals for this rule.
-
#to_bnf ⇒ Array<Rule>
Transform EBNF rule to BNF rules:.
-
#to_sxp ⇒ String
(also: #to_s)
Return SXP representation of this rule.
-
#to_ttl ⇒ String
Serializes this rule to an Turtle.
Constructor Details
#initialize(sym, id, expr, options = {}) ⇒ Rule
Returns a new instance of Rule.
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# File 'lib/ebnf/rule.rb', line 63 def initialize(sym, id, expr, = {}) @sym, @id = sym, id @expr = expr.is_a?(Array) ? expr : [:seq, expr] @ebnf = [:ebnf] @top_rule = .fetch(:top_rule, self) @kind = case when [:kind] then [: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.
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# File 'lib/ebnf/rule.rb', line 25 def comp @comp end |
#expr ⇒ Array
Rule expression
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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
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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
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# File 'lib/ebnf/rule.rb', line 50 def follow @follow end |
#id ⇒ String
ID of rule
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# File 'lib/ebnf/rule.rb', line 20 def id @id end |
#kind ⇒ :rule, ...
Kind of rule
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# File 'lib/ebnf/rule.rb', line 30 def kind @kind end |
#orig ⇒ String
Original EBNF
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# File 'lib/ebnf/rule.rb', line 40 def orig @orig end |
#start ⇒ Boolean
Indicates that this is a starting rule
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# File 'lib/ebnf/rule.rb', line 55 def start @start end |
#sym ⇒ Symbol
Symbol of rule
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# File 'lib/ebnf/rule.rb', line 16 def sym @sym end |
Instance Method Details
#<=>(other) ⇒ Object
Rules compare using their ids
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# File 'lib/ebnf/rule.rb', line 339 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
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# File 'lib/ebnf/rule.rb', line 310 def ==(other) sym == other.sym && kind == other.kind && expr == other.expr end |
#add_first(terminals) ⇒ Integer
Add terminal as proceding this rule
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# File 'lib/ebnf/rule.rb', line 253 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
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# File 'lib/ebnf/rule.rb', line 264 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 …)?
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# File 'lib/ebnf/rule.rb', line 287 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
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# File 'lib/ebnf/rule.rb', line 83 def build(expr, = {}) new_sym, new_id = (@top_rule ||self).send(:make_sym_id) Rule.new(new_sym, new_id, expr, { :kind => [:kind], :ebnf => @ebnf, :top_rule => @top_rule || self, }.merge()) end |
#equivalent?(other) ⇒ Boolean
Two rules are equivalent if they have the same #expr
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# File 'lib/ebnf/rule.rb', line 319 def equivalent?(other) expr == other.expr end |
#first_includes_eps? ⇒ Boolean
Do the firsts of this rule include the empty string?
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# File 'lib/ebnf/rule.rb', line 246 def first_includes_eps? @first && @first.include?(:_eps) end |
#for_sxp ⇒ Array
Return representation for building S-Expressions
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# File 'lib/ebnf/rule.rb', line 94 def for_sxp elements = [kind, sym, 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 301 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
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# File 'lib/ebnf/rule.rb', line 197 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 |
#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).
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# File 'lib/ebnf/rule.rb', line 328 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?
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# File 'lib/ebnf/rule.rb', line 282 def rule? kind == :rule end |
#seq? ⇒ Boolean
Is this rule of the form (seq …)?
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# File 'lib/ebnf/rule.rb', line 292 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
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# File 'lib/ebnf/rule.rb', line 234 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?
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# File 'lib/ebnf/rule.rb', line 276 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
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# File 'lib/ebnf/rule.rb', line 214 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.2))
(_a_1 [n.1] rule (op2))
* Transform (a rule (opt b)) into (a rule (alt _empty "foo"))
* 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)
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# File 'lib/ebnf/rule.rb', line 139 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
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# File 'lib/ebnf/rule.rb', line 105 def to_sxp for_sxp.to_sxp end |
#to_ttl ⇒ String
Serializes this rule to an Turtle
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# File 'lib/ebnf/rule.rb', line 113 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 |