Add remaining haskell book exercises

1 files changed, 31 insertions, 0 deletions

diff --git a/Haskell-book/24/LearnParsers/src/Text/Fractions.hs b/Haskell-book/24/LearnParsers/src/Text/Fractions.hs
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index 0000000..f09efc0
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+++ b/Haskell-book/24/LearnParsers/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
+    return (numerator % denominator)
+
+virtuousFraction :: Parser Rational
+virtuousFraction = do
+    numerator <- decimal
+    char '/'
+    denominator <- decimal
+    case denominator of
+      0 -> fail "Denominator cannot be zero"
+      _ -> return $ numerator % denominator