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| author | Joe Zhao <ztuowen@gmail.com> | 2014-08-08 14:37:06 +0800 |
|---|---|---|
| committer | Joe Zhao <ztuowen@gmail.com> | 2014-08-08 14:37:06 +0800 |
| commit | e285e81c2519dfe9b000d0f297b72c6c9909662d (patch) | |
| tree | 352ee7f112be704111da437df4f62f15a37b3be9 /solveRPN.hs | |
| parent | 423693811904a6038a1a7532700726799e05fade (diff) | |
| download | haskbox-old-e285e81c2519dfe9b000d0f297b72c6c9909662d.tar.gz haskbox-old-e285e81c2519dfe9b000d0f297b72c6c9909662d.tar.bz2 haskbox-old-e285e81c2519dfe9b000d0f297b72c6c9909662d.zip | |
Last few chapters in LYHGG
Diffstat (limited to 'solveRPN.hs')
| -rw-r--r-- | solveRPN.hs | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/solveRPN.hs b/solveRPN.hs new file mode 100644 index 0000000..051999d --- /dev/null +++ b/solveRPN.hs @@ -0,0 +1,15 @@ +import Data.List +import Control.Monad +import Text.Read + +foldingFunction :: [Double] -> String -> Maybe [Double] +foldingFunction (x:y:ys) "*" = return ((y * x):ys) +foldingFunction (x:y:ys) "/" = return ((y / x):ys) +foldingFunction (x:y:ys) "+" = return ((y + x):ys) +foldingFunction (x:y:ys) "-" = return ((y - x):ys) +foldingFunction xs numberString = liftM (:xs) (readMaybe numberString) + +solveRPN :: String -> Maybe Double +solveRPN st = do + [result] <- foldM foldingFunction [] (words st) + return result |