Parse identifiers

lib/chervil/ast.rb

 module Chervil::AST
+  require "chervil/ast/identifier"
   require "chervil/ast/number"
 end

lib/chervil/ast/identifier.rb

+module Chervil::AST
+  class Identifier
+    attr_reader :name
+
+    def initialize(name)
+      @name = name
+    end
+
+    def ==(other)
+      @name == other.name
+    end
+  end
+end

lib/chervil/lexer.rb

         if match = source.match(/^[0-9]+(\.[0-9]+)?/)
           advance(match[0].size)
           Token.new(:number, match[0])
-        elsif match = source.match(/^[a-z!$%&*\/:<=>?~_^][a-z0-9@!$%&*\/:<=>?~_^,+\-]*/)
+        elsif match = source.match(/^[a-z!$%&*\/:<=>?~_^+][a-z0-9@!$%&*\/:<=>?~_^,\-]*/)
           advance(match[0].size)
           Token.new(:identifier, match[0])
         end

lib/chervil/parser.rb

     def expr
       if @current_token.type == :number
         constant
+      elsif @current_token.type == :identifier
+        identifier
       end
     end
 
+    def identifier
+      identifier = eat(:identifier)
+      AST::Identifier.new(identifier.value)
+    end
+
     def constant
       case @current_token.type
       when :number

spec/parser_spec.rb

     end
 
     it 'parses a number' do
-      expect(parse("1").first).to eq(AST::Number.new(1.0))
+      expect(parse('1').first).to eq(AST::Number.new(1.0))
+    end
+
+    it 'parses an identifier' do
+      expect(parse('+').first).to eq(AST::Identifier.new('+'))
     end
   end
 end