chapter 24 - added module for Frations

Author: mukeshsoni

chapter24/learning-parsers/src/Text/Fractions.hs

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+{-# LANGUAGE OverloadedStrings #-}
+module Text.Fractions where
+
+import Control.Applicative
+import Data.Ratio ((%))
+import Text.Trifecta
+
+badFraction = "1/0"
+alsoBad = "10"
+shouldWork = "1/2"
+shouldAlsoWork = "2/1"
+
+parseFraction :: Parser Rational
+parseFraction = do
+    numerator <- decimal
+    char '/'
+    denominator <- decimal
+    case denominator of
+        0 -> fail "Cannot divide by zero"
+        _ -> return (numerator % denominator)
+
+main = do
+    print $ parseString parseFraction mempty badFraction
+    print $ parseString parseFraction mempty alsoBad
+    print $ parseString parseFraction mempty shouldWork
+    print $ parseString parseFraction mempty shouldAlsoWork