Allow angle brackets around EBNF symbols.

gkellogg · gkellogg · commit 27dee0672566 · 2024-11-26T16:23:28.000-08:00
Fixes #15
diff --git a/Gemfile b/Gemfile
@@ -13,6 +13,7 @@ group :development do
   gem "redcarpet",      platforms: :mri
   gem "rocco",          platforms: :mri
   gem "pygmentize",     platforms: :mri
+  gem 'getoptlong'
 end
 
 group :development, :test do
diff --git a/README.md b/README.md
@@ -75,7 +75,7 @@ Generate formatted grammar using HTML (requires [Haml][Haml] gem):
 
 ### Parsing an ISO/IEC 14977 Grammar
 
-The EBNF gem can also parse [ISO/EIC 14977] Grammars (ISOEBNF) to [S-Expressions][S-Expression].
+The EBNF gem can also parse  [ISO/IEC 14977][] Grammars (ISOEBNF) to [S-Expressions][S-Expression].
 
     grammar = EBNF.parse(File.open('./etc/iso-ebnf.isoebnf'), format: :isoebnf)
 
@@ -104,7 +104,7 @@ The [EBNF][] variant used here is based on [W3C](https://w3.org/) [EBNF][]
 as defined in the
 [XML 1.0 recommendation](https://www.w3.org/TR/REC-xml/), with minor extensions:
 
-Note that the grammar includes an optional `[identifer]` in front of rule names, which can be in conflict with the `RANGE` terminal. It is typically not a problem, but if it comes up, try parsing with the `native` parser,  add comments or sequences to disambiguate. EBNF does not have beginning of line checks as all whitespace is treated the same, so the common practice of identifying each rule inherently leads to such ambiguity.
+Note that the grammar includes an optional `[number]` in front of rule names, which can be in conflict with the `RANGE` terminal. It is typically not a problem, but if it comes up, try parsing with the `native` parser,  add comments or sequences to disambiguate. EBNF does not have beginning of line checks as all whitespace is treated the same, so the common practice of identifying each rule inherently leads to such ambiguity.
 
 The character set for EBNF is UTF-8.
 
@@ -116,7 +116,7 @@ which can also be proceeded by an optional number enclosed in square brackets to
 
     [1] symbol ::= expression
 
-(Note, this can introduce an ambiguity if the previous rule ends in a range or enum and the current rule has no identifier. In this case, enclosing `expression` within parentheses, or adding intervening comments can resolve the ambiguity.)
+(Note, this can introduce an ambiguity if the previous rule ends in a range or enum and the current rule has no number. In this case, enclosing `expression` within parentheses, or adding intervening comments can resolve the ambiguity.)
 
 Symbols are written in CAPITAL CASE if they are the start symbol of a regular language (terminals), otherwise with they are treated as non-terminal rules. Literal strings are quoted.
 
@@ -134,7 +134,7 @@ Within the expression on the right-hand side of a rule, the following expression
   <tr><td><code>[^abc], [^#xN#xN#xN]</code></td>
     <td>matches any UTF-8 R\_CHAR or HEX with a value not among the characters given. The last component may be '-'. Enumerations and ranges of excluded values may be mixed in one set of brackets.</td></tr>
   <tr><td><code>"string"</code></td>
-    <td>matches a literal string matching that given inside the double quotes.</td></tr>
+    <td>matches a literal string matching that given inside the double quotes case insensitively.</td></tr>
   <tr><td><code>'string'</code></td>
     <td>matches a literal string matching that given inside the single quotes.</td></tr>
   <tr><td><code>A (B | C)</code></td>
@@ -158,7 +158,8 @@ Within the expression on the right-hand side of a rule, the following expression
 </table>
 
 * Comments include `//` and `#` through end of line (other than hex character) and `/* ... */ (* ... *) which may cross lines`
-* All rules **MAY** start with an identifier, contained within square brackets. For example `[1] rule`, where the value within the brackets is a symbol `([a-z] | [A-Z] | [0-9] | "_" | ".")+`
+* All rules **MAY** start with an number, contained within square brackets. For example `[1] rule`, where the value within the brackets is a symbol `([a-z] | [A-Z] | [0-9] | "_" | ".")+`, which is not retained after parsing
+* Symbols **MAY** be enclosed in angle brackets `'<'` and `>`, which are dropped when parsing.
 * `@terminals` causes following rules to be treated as terminals. Any terminal which is all upper-case (eg`TERMINAL`), or any rules with expressions that match characters (`#xN`, `[a-z]`, `[^a-z]`, `[abc]`, `[^abc]`, `"string"`, `'string'`, or `A - B`), are also treated as terminals.
 * `@pass` defines the expression used to detect whitespace, which is removed in processing.
 * No support for `wfc` (well-formedness constraint) or `vc` (validity constraint).
@@ -177,7 +178,7 @@ Intermediate representations of the grammar may be serialized to Lisp-like [S-Ex
 
 is serialized as
 
-    (rule ebnf "1" (star (alt declaration rule)))
+    (rule ebnf (star (alt declaration rule)))
 
 Different components of an EBNF rule expression are transformed into their own operator:
 
diff --git a/etc/ebnf.ebnf b/etc/ebnf.ebnf
@@ -34,7 +34,9 @@
 
     [11] LHS        ::= ('[' SYMBOL ']' ' '+)? SYMBOL ' '* '::='
 
-    [12] SYMBOL     ::= ([a-z] | [A-Z] | [0-9] | '_' | '.')+
+    [12] SYMBOL     ::= '<' O_SYMBOL '>' | O_SYMBOL
+
+    [12a] O_SYMBOL  ::= ([a-z] | [A-Z] | [0-9] | '_' | '.')+
 
     [13] HEX        ::= '#x' ([a-f] | [A-F] | [0-9])+
 
diff --git a/etc/ebnf.html b/etc/ebnf.html
@@ -1,4 +1,4 @@
-<!-- Generated with ebnf version 2.4.0. See https://github.com/dryruby/ebnf. -->
+<!-- Generated with ebnf version 2.5.0. See https://github.com/dryruby/ebnf. -->
 <table class="grammar">
   <tbody id="grammar-productions" class="ebnf">
     <tr id="grammar-production-ebnf">
@@ -77,6 +77,12 @@
       <td>[12]</td>
       <td><code>SYMBOL</code></td>
       <td>::=</td>
+      <td><code class="grammar-paren">(</code>'<code class="grammar-literal">&lt;</code>' <a href="#grammar-production-O_SYMBOL">O_SYMBOL</a> '<code class="grammar-literal">&gt;</code>'<code class="grammar-paren">)</code> <code class="grammar-alt">|</code> <a href="#grammar-production-O_SYMBOL">O_SYMBOL</a></td>
+    </tr>
+    <tr id="grammar-production-O_SYMBOL">
+      <td>[12a]</td>
+      <td><code>O_SYMBOL</code></td>
+      <td>::=</td>
       <td><code class="grammar-paren">(</code><code class="grammar-brac">[</code><code class="grammar-literal">a-z</code><code class="grammar-brac">]</code> <code class="grammar-alt">|</code> <code class="grammar-brac">[</code><code class="grammar-literal">A-Z</code><code class="grammar-brac">]</code> <code class="grammar-alt">|</code> <code class="grammar-brac">[</code><code class="grammar-literal">0-9</code><code class="grammar-brac">]</code> <code class="grammar-alt">|</code> '<code class="grammar-literal">_</code>' <code class="grammar-alt">|</code> '<code class="grammar-literal">.</code>'<code class="grammar-paren">)</code><code class="grammar-plus">+</code></td>
     </tr>
     <tr id="grammar-production-HEX">
diff --git a/etc/ebnf.ll1.rb b/etc/ebnf.ll1.rb
@@ -1,4 +1,4 @@
-# This file is automatically generated by ebnf version 2.4.0
+# This file is automatically generated by ebnf version 2.5.0
 # Derived from etc/ebnf.ebnf
 module Meta
   START = :ebnf
diff --git a/etc/ebnf.ll1.sxp b/etc/ebnf.ll1.sxp
@@ -100,7 +100,8 @@
       (seq '@pass' expression))
      (terminals _terminals (seq))
      (terminal LHS "11" (seq (opt (seq '[' SYMBOL ']' (plus ' '))) SYMBOL (star ' ') '::='))
-     (terminal SYMBOL "12" (plus (alt (range "a-z") (range "A-Z") (range "0-9") '_' '.')))
+     (terminal SYMBOL "12" (alt (seq '<' O_SYMBOL '>') O_SYMBOL))
+     (terminal O_SYMBOL "12a" (plus (alt (range "a-z") (range "A-Z") (range "0-9") '_' '.')))
      (terminal HEX "13" (seq '#x' (plus (alt (range "a-f") (range "A-F") (range "0-9")))))
      (terminal RANGE "14"
       (seq '['
diff --git a/etc/ebnf.peg.rb b/etc/ebnf.peg.rb
@@ -1,4 +1,4 @@
-# This file is automatically generated by ebnf version 2.4.0
+# This file is automatically generated by ebnf version 2.5.0
 # Derived from etc/ebnf.ebnf
 module EBNFMeta
   RULES = [
@@ -25,11 +25,13 @@ module EBNFMeta
     EBNF::Rule.new(:_LHS_3, "11.3", [:seq, "[", :SYMBOL, "]", :_LHS_4], kind: :terminal).extend(EBNF::PEG::Rule),
     EBNF::Rule.new(:_LHS_4, "11.4", [:plus, " "], kind: :terminal).extend(EBNF::PEG::Rule),
     EBNF::Rule.new(:_LHS_2, "11.2", [:star, " "], kind: :terminal).extend(EBNF::PEG::Rule),
-    EBNF::Rule.new(:SYMBOL, "12", [:plus, :_SYMBOL_1], kind: :terminal).extend(EBNF::PEG::Rule),
-    EBNF::Rule.new(:_SYMBOL_1, "12.1", [:alt, :_SYMBOL_2, :_SYMBOL_3, :_SYMBOL_4, "_", "."], kind: :terminal).extend(EBNF::PEG::Rule),
-    EBNF::Rule.new(:_SYMBOL_2, "12.2", [:range, "a-z"], kind: :terminal).extend(EBNF::PEG::Rule),
-    EBNF::Rule.new(:_SYMBOL_3, "12.3", [:range, "A-Z"], kind: :terminal).extend(EBNF::PEG::Rule),
-    EBNF::Rule.new(:_SYMBOL_4, "12.4", [:range, "0-9"], kind: :terminal).extend(EBNF::PEG::Rule),
+    EBNF::Rule.new(:SYMBOL, "12", [:alt, :_SYMBOL_1, :O_SYMBOL], kind: :terminal).extend(EBNF::PEG::Rule),
+    EBNF::Rule.new(:_SYMBOL_1, "12.1", [:seq, "<", :O_SYMBOL, ">"], kind: :terminal).extend(EBNF::PEG::Rule),
+    EBNF::Rule.new(:O_SYMBOL, "12a", [:plus, :_O_SYMBOL_1], kind: :terminal).extend(EBNF::PEG::Rule),
+    EBNF::Rule.new(:_O_SYMBOL_1, "12a.1", [:alt, :_O_SYMBOL_2, :_O_SYMBOL_3, :_O_SYMBOL_4, "_", "."], kind: :terminal).extend(EBNF::PEG::Rule),
+    EBNF::Rule.new(:_O_SYMBOL_2, "12a.2", [:range, "a-z"], kind: :terminal).extend(EBNF::PEG::Rule),
+    EBNF::Rule.new(:_O_SYMBOL_3, "12a.3", [:range, "A-Z"], kind: :terminal).extend(EBNF::PEG::Rule),
+    EBNF::Rule.new(:_O_SYMBOL_4, "12a.4", [:range, "0-9"], kind: :terminal).extend(EBNF::PEG::Rule),
     EBNF::Rule.new(:HEX, "13", [:seq, "#x", :_HEX_1], kind: :terminal).extend(EBNF::PEG::Rule),
     EBNF::Rule.new(:_HEX_1, "13.1", [:plus, :_HEX_2], kind: :terminal).extend(EBNF::PEG::Rule),
     EBNF::Rule.new(:_HEX_2, "13.2", [:alt, :_HEX_3, :_HEX_4, :_HEX_5], kind: :terminal).extend(EBNF::PEG::Rule),
diff --git a/etc/ebnf.peg.sxp b/etc/ebnf.peg.sxp
@@ -22,11 +22,13 @@
      (terminal _LHS_3 "11.3" (seq '[' SYMBOL ']' _LHS_4))
      (terminal _LHS_4 "11.4" (plus ' '))
      (terminal _LHS_2 "11.2" (star ' '))
-     (terminal SYMBOL "12" (plus _SYMBOL_1))
-     (terminal _SYMBOL_1 "12.1" (alt _SYMBOL_2 _SYMBOL_3 _SYMBOL_4 '_' '.'))
-     (terminal _SYMBOL_2 "12.2" (range "a-z"))
-     (terminal _SYMBOL_3 "12.3" (range "A-Z"))
-     (terminal _SYMBOL_4 "12.4" (range "0-9"))
+     (terminal SYMBOL "12" (alt _SYMBOL_1 O_SYMBOL))
+     (terminal _SYMBOL_1 "12.1" (seq '<' O_SYMBOL '>'))
+     (terminal O_SYMBOL "12a" (plus _O_SYMBOL_1))
+     (terminal _O_SYMBOL_1 "12a.1" (alt _O_SYMBOL_2 _O_SYMBOL_3 _O_SYMBOL_4 '_' '.'))
+     (terminal _O_SYMBOL_2 "12a.2" (range "a-z"))
+     (terminal _O_SYMBOL_3 "12a.3" (range "A-Z"))
+     (terminal _O_SYMBOL_4 "12a.4" (range "0-9"))
      (terminal HEX "13" (seq '#x' _HEX_1))
      (terminal _HEX_1 "13.1" (plus _HEX_2))
      (terminal _HEX_2 "13.2" (alt _HEX_3 _HEX_4 _HEX_5))
diff --git a/etc/ebnf.sxp b/etc/ebnf.sxp
@@ -12,7 +12,8 @@
      (rule pass "10" (seq '@pass' expression))
      (terminals _terminals (seq))
      (terminal LHS "11" (seq (opt (seq '[' SYMBOL ']' (plus ' '))) SYMBOL (star ' ') '::='))
-     (terminal SYMBOL "12" (plus (alt (range "a-z") (range "A-Z") (range "0-9") '_' '.')))
+     (terminal SYMBOL "12" (alt (seq '<' O_SYMBOL '>') O_SYMBOL))
+     (terminal O_SYMBOL "12a" (plus (alt (range "a-z") (range "A-Z") (range "0-9") '_' '.')))
      (terminal HEX "13" (seq '#x' (plus (alt (range "a-f") (range "A-F") (range "0-9")))))
      (terminal RANGE "14"
       (seq '['
diff --git a/lib/ebnf/ebnf/meta.rb b/lib/ebnf/ebnf/meta.rb
@@ -1,4 +1,4 @@
-# This file is automatically generated by ebnf version 2.0.0
+# This file is automatically generated by ebnf version 2.5.0
 # Derived from etc/ebnf.ebnf
 module EBNFMeta
   RULES = [
@@ -25,11 +25,13 @@ module EBNFMeta
     EBNF::Rule.new(:_LHS_3, "11.3", [:seq, "[", :SYMBOL, "]", :_LHS_4], kind: :terminal).extend(EBNF::PEG::Rule),
     EBNF::Rule.new(:_LHS_4, "11.4", [:plus, " "], kind: :terminal).extend(EBNF::PEG::Rule),
     EBNF::Rule.new(:_LHS_2, "11.2", [:star, " "], kind: :terminal).extend(EBNF::PEG::Rule),
-    EBNF::Rule.new(:SYMBOL, "12", [:plus, :_SYMBOL_1], kind: :terminal).extend(EBNF::PEG::Rule),
-    EBNF::Rule.new(:_SYMBOL_1, "12.1", [:alt, :_SYMBOL_2, :_SYMBOL_3, :_SYMBOL_4, "_", "."], kind: :terminal).extend(EBNF::PEG::Rule),
-    EBNF::Rule.new(:_SYMBOL_2, "12.2", [:range, "a-z"], kind: :terminal).extend(EBNF::PEG::Rule),
-    EBNF::Rule.new(:_SYMBOL_3, "12.3", [:range, "A-Z"], kind: :terminal).extend(EBNF::PEG::Rule),
-    EBNF::Rule.new(:_SYMBOL_4, "12.4", [:range, "0-9"], kind: :terminal).extend(EBNF::PEG::Rule),
+    EBNF::Rule.new(:SYMBOL, "12", [:alt, :_SYMBOL_1, :O_SYMBOL], kind: :terminal).extend(EBNF::PEG::Rule),
+    EBNF::Rule.new(:_SYMBOL_1, "12.1", [:seq, "<", :O_SYMBOL, ">"], kind: :terminal).extend(EBNF::PEG::Rule),
+    EBNF::Rule.new(:O_SYMBOL, "12a", [:plus, :_O_SYMBOL_1], kind: :terminal).extend(EBNF::PEG::Rule),
+    EBNF::Rule.new(:_O_SYMBOL_1, "12a.1", [:alt, :_O_SYMBOL_2, :_O_SYMBOL_3, :_O_SYMBOL_4, "_", "."], kind: :terminal).extend(EBNF::PEG::Rule),
+    EBNF::Rule.new(:_O_SYMBOL_2, "12a.2", [:range, "a-z"], kind: :terminal).extend(EBNF::PEG::Rule),
+    EBNF::Rule.new(:_O_SYMBOL_3, "12a.3", [:range, "A-Z"], kind: :terminal).extend(EBNF::PEG::Rule),
+    EBNF::Rule.new(:_O_SYMBOL_4, "12a.4", [:range, "0-9"], kind: :terminal).extend(EBNF::PEG::Rule),
     EBNF::Rule.new(:HEX, "13", [:seq, "#x", :_HEX_1], kind: :terminal).extend(EBNF::PEG::Rule),
     EBNF::Rule.new(:_HEX_1, "13.1", [:plus, :_HEX_2], kind: :terminal).extend(EBNF::PEG::Rule),
     EBNF::Rule.new(:_HEX_2, "13.2", [:alt, :_HEX_3, :_HEX_4, :_HEX_5], kind: :terminal).extend(EBNF::PEG::Rule),
diff --git a/lib/ebnf/native.rb b/lib/ebnf/native.rb
@@ -52,7 +52,7 @@ def eachRule(scanner)
           yield r unless r.empty?
           #debug("eachRule(rule)") { "[#{cur_lineno}] #{s.inspect}" }
           @lineno = cur_lineno
-          r = s
+          r = s.gsub(/[<>]/, '') # Remove angle brackets
         else
           # Collect until end of line, or start of comment or quote
           s = scanner.scan_until(%r{(?:[/\(]\*)|#(?!x)|//|["']|$})
@@ -81,6 +81,7 @@ def ruleParts(rule)
       num, sym = num_sym.split(']', 2).map(&:strip)
       num, sym = "", num if sym.nil?
       num = num[1..-1]
+      sym = sym[1..-2] if sym.start_with?('<') && sym.end_with?('>')
       r = Rule.new(sym && sym.to_sym, num, expression(expr).first, ebnf: self)
       debug("ruleParts") { r.inspect }
       r
@@ -226,7 +227,7 @@ def diff(s)
     #     (a ' b c')
     #     
     #     >>> postfix("a? b c")
-    #     ((opt, a) ' b c')
+    #     ((opt a) ' b c')
     def postfix(s)
       debug("postfix") {"(#{s.inspect})"}
       e, s = depth {primary(s)}
@@ -297,8 +298,8 @@ def terminal(s)
         s.match(/(#x\h+)(.*)$/)
         l, s = $1, $2
         [[:hex, l], s]
-      when /[\w\.]/ # SYMBOL
-        s.match(/([\w\.]+)(.*)$/)
+      when '<', /[\w\.]/ # SYMBOL
+        s.match(/<?([\w\.]+)>?(.*)$/)
         l, s = $1, $2
         [l.to_sym, s]
       when '-'
diff --git a/lib/ebnf/parser.rb b/lib/ebnf/parser.rb
@@ -26,15 +26,17 @@ class Parser
 
     # Match the Left hand side of a rule or terminal
     #
-    #     [11] LHS        ::= ('[' SYMBOL+ ']' ' '+)? SYMBOL ' '* '::='
+    #     [11] LHS        ::= ('[' SYMBOL+ ']' ' '+)? <? SYMBOL >? ' '* '::='
     terminal(:LHS, LHS) do |value, prod|
-      value.to_s.scan(/(?:\[([^\]]+)\])?\s*(\w+)\s*::=/).first
+      value.to_s.scan(/(?:\[([^\]]+)\])?\s*<?(\w+)>?\s*::=/).first
     end
 
     # Match `SYMBOL` terminal
     #
-    #     [12] SYMBOL     ::= ([a-z] | [A-Z] | [0-9] | '_' | '.')+
+    #     [12] SYMBOL     ::= '<' O_SYMBOL '>' | O_SYMBOL
+    #     [12a] O_SYMBOL  ::= ([a-z] | [A-Z] | [0-9] | '_' | '.')+
     terminal(:SYMBOL, SYMBOL) do |value|
+      value = value[1..-2] if value.start_with?('<') && value.end_with?('>')
       value.to_sym
     end
 
@@ -266,10 +268,10 @@ class Parser
     # @return [EBNFParser]
     def initialize(input, **options, &block)
       # If the `level` option is set, instantiate a logger for collecting trace information.
-      if options.has_key?(:level)
-        options[:logger] = Logger.new(STDERR)
-        options[:logger].level = options[:level]
-        options[:logger].formatter = lambda {|severity, datetime, progname, msg| "#{severity} #{msg}\n"}
+      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
 
       # Read input, if necessary, which will be used in a Scanner.
diff --git a/lib/ebnf/terminals.rb b/lib/ebnf/terminals.rb
@@ -2,12 +2,12 @@
 # Terminal definitions for the EBNF grammar
 module EBNF::Terminals
   SYMBOL_BASE  = %r(\b[a-zA-Z0-9_\.]+\b)u.freeze
-  SYMBOL  = %r(#{SYMBOL_BASE}(?!\s*::=))u.freeze
+  SYMBOL  = %r(<?#{SYMBOL_BASE}>?(?!\s*::=))u.freeze
   HEX     = %r(\#x\h+)u.freeze
   CHAR    = %r([\u0009\u000A\u000D\u0020-\uD7FF\u{10000}-\u{10FFFF}])u.freeze
   R_CHAR  = %r([\u0009\u000A\u000D\u0020-\u002C\u002E-\u005C\u005E-\uD7FF\u{10000}-\u{10FFFF}])u.freeze
-  RANGE   = %r(\[(?:(?:#{R_CHAR}\-#{R_CHAR})|(?:#{HEX}\-#{HEX})|#{R_CHAR}|#{HEX})+-?\](?!\s+#{SYMBOL_BASE}\s*::=))u.freeze
-  LHS     = %r((?:\[#{SYMBOL_BASE}\])?\s*#{SYMBOL_BASE}\s*::=)u.freeze
+  RANGE   = %r(\[(?:(?:#{R_CHAR}\-#{R_CHAR})|(?:#{HEX}\-#{HEX})|#{R_CHAR}|#{HEX})+-?\](?!\s+<?#{SYMBOL_BASE}>?\s*::=))u.freeze
+  LHS     = %r((?:\[#{SYMBOL_BASE}\])?\s*<?#{SYMBOL_BASE}>?\s*::=)u.freeze
   O_RANGE = %r(\[\^(?:(?:#{R_CHAR}\-#{R_CHAR})|(?:#{HEX}\-#{HEX}|#{R_CHAR}|#{HEX}))+-?\])u.freeze
   STRING1 = %r("[\u0009\u000A\u000D\u0020\u0021\u0023-\uD7FF\u{10000}-\u{10FFFF}]*")u.freeze
   STRING2 = %r('[\u0009\u000A\u000D\u0020-\u0026\u0028-\uD7FF\u{10000}-\u{10FFFF}]*')u.freeze
diff --git a/spec/ebnf_spec.rb b/spec/ebnf_spec.rb
@@ -30,6 +30,14 @@
                     |   STRING2
                     |   '(' expression ')'
       } => %{((rule primary (alt HEX RANGE O_RANGE STRING1 STRING2 (seq '(' expression ')'))))},
+      %{
+        <primary>   ::= <HEX>
+                    |   <RANGE>
+                    |   <O_RANGE>
+                    |   <STRING1>
+                    |   <STRING2>
+                    |   '(' <expression> ')'
+      } => %{((rule primary (alt HEX RANGE O_RANGE STRING1 STRING2 (seq '(' expression ')'))))},
     }.each do |input, expected|
       context input do
         subject {EBNF.parse(input)}
diff --git a/spec/native_spec.rb b/spec/native_spec.rb
@@ -60,6 +60,10 @@
           %{Prolog    ::=           BaseDecl? PrefixDecl*},
           %{((rule Prolog (seq (opt BaseDecl) (star PrefixDecl))))}
         ],
+        "prolog (with brackets)": [
+          %{<Prolog>    ::=           <BaseDecl>? <PrefixDecl>*},
+          %{((rule Prolog (seq (opt BaseDecl) (star PrefixDecl))))}
+        ],
         "aliteration": [
           %{declaration ::= '@terminals' | '@pass'},
           %{((rule declaration (alt '@terminals' '@pass')))},
@@ -111,7 +115,7 @@
       %{NCCHAR1 | '-' | [0-9] | #x00B7 | [#x0300-#x036F] | [#x203F-#x2040]} =>
         %{(alt NCCHAR1 '-' (range "0-9") (hex "#x00B7") (range "#x0300-#x036F") (range "#x203F-#x2040"))},
       %{'<' ([^<>"{}|^`\]-[#x00-#x20] | UCHAR)* '>'} =>
-        %{(seq '<' (star (alt (diff (range "^<>\\\"{}|^`") (range "#x00-#x20")) UCHAR)) '>')}
+        %{(seq '<' (star (alt (diff (range "^<>\\\"{}|^`") (range "#x00-#x20")) UCHAR)) '>')},
     }.each do |input, expected|
       it "given #{input.inspect} produces #{expected}" do
         rule = parse("rule ::= #{input}").ast.first
diff --git a/spec/peg_spec.rb b/spec/peg_spec.rb
@@ -20,8 +20,28 @@
                         |   '(' expression ')'
         
       } =>
-        %{((rule primary "9" (alt HEX RANGE O_RANGE STRING1 STRING2 _primary_1))
-           (rule _primary_1 "9.1" (seq '(' expression ')')))},
+      %{((rule primary "9" (alt HEX RANGE O_RANGE STRING1 STRING2 _primary_1))
+         (rule _primary_1 "9.1" (seq '(' expression ')')))},
+      %{
+        primary     ::= HEX
+                    |   RANGE
+                    |   O_RANGE
+                    |   STRING1
+                    |   STRING2
+                    |   '(' expression ')'
+      } =>
+      %{((rule primary (alt HEX RANGE O_RANGE STRING1 STRING2 _primary_1))
+         (rule _primary_1 (seq '(' expression ')')))},
+      %{
+        <primary>   ::= <HEX>
+                    |   <RANGE>
+                    |   <O_RANGE>
+                    |   <STRING1>
+                    |   <STRING2>
+                    |   '(' <expression> ')'
+      } =>
+      %{((rule primary (alt HEX RANGE O_RANGE STRING1 STRING2 _primary_1))
+         (rule _primary_1 (seq '(' expression ')')))},
       %{[1] start ::= A B C} =>
         %{((rule start "1" (seq A B C)))},
       %{[1] start ::= A B? C* D+} =>
diff --git a/spec/rule_spec.rb b/spec/rule_spec.rb

Original file line number	Diff line number	Diff line change
`@@ -1,4 +1,4 @@`
`1`		`-# This file is automatically generated by ebnf version 2.4.0`
	`1`	`+# This file is automatically generated by ebnf version 2.5.0`
`2`	`2`	`# Derived from etc/ebnf.ebnf`
`3`	`3`	`module Meta`
`4`	`4`	`START = :ebnf`