From 98329e0a3dd4f78b5d815ac3896272ec70904901 Mon Sep 17 00:00:00 2001
From: Eugen Wissner <belka@caraus.de>
Date: Thu, 11 Dec 2025 10:28:11 +0100
Subject: Add remaining haskell book exercises

---
 Haskell-book/24/ParserExercises/src/PhoneNumber.hs | 28 ++++++++++++++++++++++
 1 file changed, 28 insertions(+)
 create mode 100644 Haskell-book/24/ParserExercises/src/PhoneNumber.hs

(limited to 'Haskell-book/24/ParserExercises/src/PhoneNumber.hs')

diff --git a/Haskell-book/24/ParserExercises/src/PhoneNumber.hs b/Haskell-book/24/ParserExercises/src/PhoneNumber.hs
new file mode 100644
index 0000000..dad75a7
--- /dev/null
+++ b/Haskell-book/24/ParserExercises/src/PhoneNumber.hs
@@ -0,0 +1,28 @@
+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)
-- 
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