27 lines
716 B
Haskell
27 lines
716 B
Haskell
import qualified Lambda as L
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import Data.Maybe
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-- Helper type for using arbitrary strings as symbols
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newtype StrSymbol = StrSymbol String
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instance Show StrSymbol where
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show (StrSymbol s) = s
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instance Eq StrSymbol where
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(StrSymbol a) == (StrSymbol b) = a == b
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-- process a string line by line instead of all at once
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linewise :: (String -> String) -> String -> String
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linewise f = unlines . map f . lines
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evaluate :: String -> String
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evaluate s =
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let result = return
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. map (L.display True)
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. L.evaluate
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. fmap StrSymbol
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l = fromMaybe ["Error: Could not parse expression."]
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$ L.parseMaybe s >>= result
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in unlines l
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main = interact $ linewise evaluate
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