Merge pull request #15 from ford-prefect/custom-error

Add a toAff' for native code that does not fail with Errors or strings

src/Control/Promise.purs

@@ -1,4 +1,4 @@
-module Control.Promise (fromAff, toAff, toAffE, Promise()) where
+module Control.Promise (fromAff, toAff, toAff', toAffE, Promise()) where
 
 import Prelude
 
@@ -37,10 +37,16 @@ coerce fn =
 -- | coerce the error value into an actual JavaScript Error object. We can do this
 -- | with Error objects or Strings. Anything else gets a "dummy" Error object.
 toAff :: forall a. Promise a -> Aff a
-toAff p = makeAff
+toAff = toAff' coerce
+
+-- | Convert a Promise into an Aff with custom Error coercion.
+-- | When the promise rejects, we attempt to coerce the error value into an
+-- | actual JavaScript Error object using the provided function.
+toAff' :: forall a. (Foreign -> Error) -> Promise a -> Aff a
+toAff' customCoerce p = makeAff
   (\cb -> mempty <$ thenImpl
     p
-    (mkEffectFn1 $ cb <<< Left <<< coerce)
+    (mkEffectFn1 $ cb <<< Left <<< customCoerce)
     (mkEffectFn1 $ cb <<< Right))
 
 -- | Utility to convert an Effect returning a Promise into an Aff (i.e. the inverse of fromAff)

test/Main.js

@@ -1,3 +1,4 @@
 exports.helloPromise = Promise.resolve("Hello");
 exports.goodbyePromise = Promise.reject("Goodbye");
 exports.errPromise = Promise.reject(new Error('err'));
+exports.customErrPromise = Promise.reject({ code: "err" });

test/Main.purs

@@ -2,14 +2,16 @@ module Test.Main where
 
 import Prelude
 
-import Control.Monad.Except (throwError)
+import Control.Monad.Except (runExcept, throwError)
 import Control.Promise (Promise)
 import Control.Promise as Promise
 import Data.Either (either)
 import Effect (Effect)
 import Effect.Aff (attempt)
 import Effect.Class (liftEffect)
-import Effect.Exception (message, error)
+import Effect.Exception (error, message)
+import Foreign (readString, unsafeFromForeign)
+import Foreign.Index (readProp)
 import Test.Unit (suite, test, timeout)
 import Test.Unit.Assert as Assert
 import Test.Unit.Main (runTest)
@@ -18,6 +20,8 @@ foreign import helloPromise :: Promise String
 
 foreign import errPromise :: Promise String
 
+foreign import customErrPromise :: Promise String
+
 foreign import goodbyePromise :: Promise String
 
 main :: Effect Unit
@@ -29,6 +33,9 @@ main = runTest do
     test "err" do
       res <- attempt $ Promise.toAff errPromise
       Assert.equal "err" $ either message (const "-") res
+    test "customErr" do
+      res <- attempt $ Promise.toAff' errorCodeCoerce customErrPromise
+      Assert.equal "err" $ either message (const "-") res
     test "Goodbye" do
       res <- attempt $ Promise.toAff goodbyePromise
       Assert.equal "Goodbye" $ either message (const "-") res
@@ -46,3 +53,6 @@ main = runTest do
       promise <- liftEffect $ Promise.fromAff $ throwError $ error "err123"
       res <- attempt $ Promise.toAff promise
       Assert.equal "err123" $ either message (const "-") res
+  where
+    errorCodeCoerce v = either (\_ -> error "fail") error $
+                          (runExcept $ readProp "code" (unsafeFromForeign v) >>= readString)