Add some missing unscans to PEG rule parser.

lib/ebnf/peg/parser.rb

@@ -91,8 +91,7 @@ def terminal(term, regexp = nil, **options, &block)
 
       ##
       # Defines a production called at the beggining of a particular production
-      # with data from previous production along with data defined for the
-      # current production. Block is called in an evaluation block from
+      # with data from previous production. Block is called in an evaluation block from
       # the enclosing parser.
       #
       # @param [Symbol] term

lib/ebnf/peg/rule.rb

@@ -89,6 +89,7 @@ def parse(input, **options)
           when String
             # If the input matches any terminal, then it can't be treated as a string
             if matched = parser.class.terminal_regexps.detect {|sym, re| input.scan(re)}
+              input.unscan  # Reset scan position
               :unmatched
             else
               s = input.scan(Regexp.new(Regexp.quote(prod), string_regexp_opts))
@@ -136,6 +137,7 @@ def parse(input, **options)
           rule.parse(input, **options)
         when String
           if matched = parser.class.terminal_regexps.detect {|sym, re| input.scan(re)}
+            input.unscan  # Reset scan position
             :unmatched
           else
             s = input.scan(Regexp.new(Regexp.quote(prod), string_regexp_opts))
@@ -194,6 +196,7 @@ def parse(input, **options)
             rule.parse(input, **options.merge(_rept_data: accumulator))
           when String
             if matched = parser.class.terminal_regexps.detect {|sym, re| input.scan(re)}
+              input.unscan  # Reset scan position
               :unmatched
             else
               s = input.scan(Regexp.new(Regexp.quote(prod), string_regexp_opts))