Merge pull request #1 from purescript/error

Use Error type for exceptions

Author: paf31

README.md

@@ -4,11 +4,24 @@
 
 ### Types
 
-    data Exception :: * -> !
+    data Error :: *
+
+    data Exception :: !
+
+
+### Type Class Instances
+
+    instance showError :: Show Error
 
 
 ### Values
 
-    catchException :: forall e r a. (e -> Eff r a) -> Eff (err :: Exception e | r) a -> Eff r a
+    catchException :: forall a eff. (Error -> Eff eff a) -> Eff (err :: Exception | eff) a -> Eff eff a
+
+    error :: String -> Error
+
+    message :: Error -> String
+
+    showErrorImpl :: Error -> String
 
-    throwException :: forall a e r. e -> Eff (err :: Exception e | r) a
+    throwException :: forall a eff. Error -> Eff (err :: Exception | eff) a

src/Control/Monad/Eff/Exception.purs

@@ -2,14 +2,34 @@ module Control.Monad.Eff.Exception where
 
 import Control.Monad.Eff
 
-foreign import data Exception :: * -> !
+foreign import data Exception :: !
 
+foreign import data Error :: *
+
+instance showError :: Show Error where
+  show = showErrorImpl
+
+foreign import showErrorImpl
+  "function showErrorImpl(err) {\
+  \  return err.stack ? err.stack : err.toString();\
+  \}" :: Error -> String
+
+foreign import error
+  "function error(msg) {\
+  \  return new Error(msg);\
+  \};" :: String -> Error
+
+foreign import message 
+  "function message(e) {\
+  \  return e.message;\
+  \}" :: Error -> String
+  
 foreign import throwException 
   "function throwException(e) {\
   \  return function() {\
   \    throw e;\
   \  };\
-  \}" :: forall a e r. e -> Eff (err :: Exception e | r) a
+  \}" :: forall a eff. Error -> Eff (err :: Exception | eff) a
 
 foreign import catchException 
   "function catchException(c) {\
@@ -18,8 +38,12 @@ foreign import catchException
   \      try {\
   \        return t();\
   \      } catch(e) {\
-  \        return c(e)();\
+  \        if (e instanceof Error) {\
+  \          return c(e)();\
+  \        } else {\
+  \          throw e;\
+  \        }\
   \      }\
   \    };\
   \  };\
-  \}" :: forall e r a. (e -> Eff r a) -> Eff (err :: Exception e | r) a -> Eff r a
+  \}" :: forall a eff. (Error -> Eff eff a) -> Eff (err :: Exception | eff) a -> Eff eff a