replace scotty deprecated raise with scotty throw for 500 errors

replace deprecated scotty param function
resolves #372

examples/Plantfarm.hs

@@ -6,15 +6,14 @@
 
 {-# LANGUAGE DerivingVia #-}
 
-
+import Control.Monad.Catch (Exception)
 import Codec.Winery (Serialise, WineryVariant(WineryVariant))
 import Control.DeepSeq (NFData)
 import Data.Aeson (FromJSON, ToJSON(toEncoding, toJSON))
 import Data.Data (Proxy(Proxy))
 import Data.Either (lefts, rights)
 import Data.Functor (($>))
-import Data.Text as T (Text)
-import qualified Data.Text.Lazy as TL (pack)
+import Data.Text as T (Text,pack)
 import GHC.Generics (Generic)
 import qualified ProjectM36.Base as Base
 import ProjectM36.DatabaseContext
@@ -147,7 +146,7 @@ main = do
 
     --  retrieve a plant by name
     S.get "/plant/:name" $ do
-        n <- S.param "name"
+        n <- S.pathParam "name"
         e <- liftIO $ getPlant c n
         p <- handleWebError e
         S.json p
@@ -170,7 +169,7 @@ main = do
     --  watering the plant having the provided name.
     --  This will water the plant and might let it progress to the next stage. It might also die.
     S.post "/plant/water/:name" $ do
-      n <- S.param "name"
+      n <- S.pathParam "name"
       e <- liftIO $ waterPlant c n
       p <- handleWebError e
       S.json p
@@ -190,14 +189,14 @@ main = do
 
     --  deleting all plants at a specific stage
     S.delete "/plants?stage=:stage" $ do
-      s <- S.param "stage"
+      s <- S.pathParam "stage"
       e <- liftIO $ deletePlantsByStage c s
       p <- handleWebError e
       S.json p
 
     --  deleting all plants at a specific stage
     S.delete "/plants" $ do
-      s <- S.param "name"
+      s <- S.queryParam "name"
       e <- liftIO $ deletePlantByName c s
       p <- handleWebError e
       S.json p
@@ -208,15 +207,20 @@ main = do
       ps <- handleWebErrors e
       S.json ps
 
+data WebError = WebError T.Text
+ deriving Show
+
+instance Exception WebError
+
 handleWebError :: Either Err b -> S.ActionM b
-handleWebError (Left e) = S.raise (TL.pack $ "An error occurred:\n" <> show e)
+handleWebError (Left e) = S.throw (WebError (T.pack $ "An error occurred:\n" <> show e))
 handleWebError (Right v) = pure v
 
 handleWebErrors :: [Either Err b] -> S.ActionM [b]
 handleWebErrors e = do
   case lefts e of
     [] -> pure (rights e)
-    l -> S.raise (TL.pack $ "Errors occurred:\n" <> concatMap ((<>"\n") . show) l)
+    l -> S.throw (WebError (T.pack $ "Errors occurred:\n" <> concatMap ((<>"\n") . show) l))
 
 
 -- |    watering a plant and thereby possibly updating its stage