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28 lines
682 B
Idris
28 lines
682 B
Idris
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toBit : Num i => Char -> Maybe i
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toBit '0' = Just 0
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toBit '1' = Just 1
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toBit _ = Nothing
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-- Return the number represented in binary as an initial segment of
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-- the string (remembering that if a number begins 0, it's zero).
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eatBinary : (Eq i, Num i) => String -> i
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eatBinary = firstDigit . unpack where
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laterDigit : i -> List Char -> i
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laterDigit n [] = n
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laterDigit n (d :: ds) = let
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f : Maybe i -> i
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f Nothing = n
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f (Just a) = laterDigit (2*n + a) ds
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in f $ toBit d
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firstDigit : List Char -> i
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firstDigit [] = 0
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firstDigit (d :: ds) = let
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f : Maybe i -> i
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f Nothing = 0
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f (Just 0) = 0
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f (Just a) = laterDigit a ds
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in f $ toBit d
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