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------------------------------------------------------------------------------ --- Library with some functions for reading and converting numeric tokens. -- --- @author Michael Hanus, Frank Huch, Bjoern Peemoeller --- @version November 2016 --- @category general ------------------------------------------------------------------------------ module ReadNumeric ( readInt, readNat, readHex, readOct, readBin ) where import Char (digitToInt, isBinDigit, isOctDigit, isDigit, isHexDigit, isSpace) --- Read a (possibly negative) integer as a first token in a string. --- The string might contain leadings blanks and the integer is read --- up to the first non-digit. --- If the string does not start with an integer token, `Nothing` is returned, --- otherwise the result is `Just (v, s)`, where `v` is the value of the integer --- and `s` is the remaing string without the integer token. readInt :: String -> Maybe (Int, String) readInt str = case dropWhile isSpace str of [] -> Nothing '-':str1 -> maybe Nothing (\ (val,rstr) -> Just (-val,rstr)) (readNat str1) str1 -> readNat str1 --- Read a natural number as a first token in a string. --- The string might contain leadings blanks and the number is read --- up to the first non-digit. --- If the string does not start with a natural number token, --- `Nothing` is returned, --- otherwise the result is `Just (v, s)` where `v` is the value of the number --- and s is the remaing string without the number token. readNat :: String -> Maybe (Int, String) readNat str = readNumPrefix (dropWhile isSpace str) Nothing 10 isDigit digitToInt --- Read a hexadecimal number as a first token in a string. --- The string might contain leadings blanks and the number is read --- up to the first non-hexadecimal digit. --- If the string does not start with a hexadecimal number token, --- `Nothing` is returned, --- otherwise the result is `Just (v, s)` where `v` is the value of the number --- and s is the remaing string without the number token. readHex :: String -> Maybe (Int, String) readHex l = readNumPrefix (dropWhile isSpace l) Nothing 16 isHexDigit digitToInt --- Read an octal number as a first token in a string. --- The string might contain leadings blanks and the number is read --- up to the first non-octal digit. --- If the string does not start with an octal number token, --- `Nothing` is returned, --- otherwise the result is `Just (v, s)` where `v` is the value of the number --- and s is the remaing string without the number token. readOct :: String -> Maybe (Int, String) readOct l = readNumPrefix (dropWhile isSpace l) Nothing 8 isOctDigit digitToInt --- Read a binary number as a first token in a string. --- The string might contain leadings blanks and the number is read --- up to the first non-binary digit. --- If the string does not start with a binary number token, --- `Nothing` is returned, --- otherwise the result is `Just (v, s)` where `v` is the value of the number --- and s is the remaing string without the number token. readBin :: String -> Maybe (Int, String) readBin l = readNumPrefix (dropWhile isSpace l) Nothing 2 isBinDigit digitToInt --- Read an integral number prefix where the value of an already read number --- prefix is provided as the second argument. --- The third argument is the base, the fourth argument --- is a predicate to distinguish valid digits, and the fifth argument converts --- valid digits into integer values. readNumPrefix :: String -> Maybe Int -> Int -> (Char -> Bool) -> (Char -> Int) -> Maybe (Int, String) readNumPrefix [] Nothing _ _ _ = Nothing readNumPrefix [] (Just n) _ _ _ = Just (n,"") readNumPrefix (c:cs) (Just n) base isdigit valueof | isdigit c = readNumPrefix cs (Just (base*n+valueof c)) base isdigit valueof | otherwise = Just (n,c:cs) readNumPrefix (c:cs) Nothing base isdigit valueof | isdigit c = readNumPrefix cs (Just (valueof c)) base isdigit valueof | otherwise = Nothing |