Basic expression parsing

lib/liquid/lexer.rb

@@ -21,7 +21,9 @@ module Liquid
       '|' => :pipe,
       '.' => :dot,
       ':' => :colon,
-      ',' => :comma
+      ',' => :comma,
+      '[' => :open_square,
+      ']' => :close_square
     }
     IDENTIFIER = /[\w\-]+/
     SINGLE_STRING_LITERAL = /'[^\']*'/
@@ -56,7 +58,7 @@ module Liquid
       else
         c = @ss.getch
         if s = SPECIALS[c]
-          return Token[s]
+          return Token[s,c]
         end
 
         raise SyntaxError, "Unexpected character #{c}."

lib/liquid/parser.rb

@@ -8,19 +8,51 @@ module Liquid
       @p = 0 # pointer to current location
     end
 
-    def consume(type)
+    def consume(type = nil)
       token = @tokens[@p]
-      if match && token.type != type
+      if type && token.type != type
-        raise SyntaxError, "Expected #{match} but found #{@tokens[@p]}"
+        raise SyntaxError, "Expected #{type} but found #{@tokens[@p]}"
       end
       @p += 1
-      token
+      token.contents
+    end
+
+    def cur_token()
+      tok = @tokens[@p]
+      raise SyntaxError, 'Expected more input.' unless tok
+      tok
     end
 
     def look(type)
-      @tokens[@p].type == type
+      tok = @tokens[@p]
+      return false unless tok
+      tok.type == type
     end
 
     # === General Liquid parsing functions ===
+
+    def expression
+      token = cur_token
+      if token.type == :id
+        variable_signature
+      elsif [:string, :integer, :float].include? token.type
+        token.contents
+      else
+        raise SyntaxError, "#{token} is not a valid expression."
+      end
+    end
+
+    def variable_signature
+      str = consume(:id)
+      if look(:dot)
+        str << consume
+        str << variable_signature
+      elsif look(:open_square)
+        str << consume
+        str << expression
+        str << consume(:close_square)
+      end
+      str
+    end
   end
 end