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+module PhoneNumber where
+
+import Control.Applicative
+import Text.Trifecta
+
+-- 4. Write a parser for US/Canada phone numbers with varying formats.
+-- Cf. Wikipeida's article on "National conventions for writing telephone
+-- numbers". You are encouraged to adapt the exercise to your locality's
+-- conventions if they are not part of the NNAP scheme.
+
+-- aka area code
+type NumberingPlanArea = Int
+type Exchange = Int
+type LineNumber = Int
+
+data PhoneNumber = PhoneNumber NumberingPlanArea Exchange LineNumber
+    deriving (Eq, Show)
+
+parsePhone :: Parser PhoneNumber
+parsePhone = do
+    _ <- optional ((try $ char '(') <|> (try (char '1' >> char '-')))
+    area <- count 3 digit
+    _ <- optional $ (try $ char ')')
+    _ <- optional $  (try $ char ' ') <|> (try $ char '-')
+    exchange <- count 3 digit
+    _ <- optional $ (char ' ') <|> (char '-')
+    lineNumber <- decimal
+    return $ PhoneNumber (read area) (read exchange) (fromIntegral lineNumber)