On 9/26/12 4:53 PM, Ertugrul Söylemez wrote:

Bryce Verdier wrote:

...

This is the new code that is trying to use try (imported from Control.Exception) getGoogR = do body <- try {- [...] -}

[...]

I'm sure that my problem has a simple fix, but I just don't know what it is. I will be happy to share any other code if people ask, I'm just giving the short version for brevities sake. The fix is indeed simple. In fact you're just using the wrong 'try', because Yesod handlers aren't IO actions, but actions in a monad that is specific to your application, called Handler. The error message suggests that, although the type is spelled out completely there.

What you want is the lifted version of 'try', which you find in the Control.Exception.Lifted module.

Greets, Ertugrul

Thank you for the reply Ertugrul, sadly that didn't seem to help. :( Here are my changes: import qualified Control.Exception.Lifted as L ... body <- L.try (simpleHttp "http://www.google.com") :: IO (Either L.SomeException Data.ByteString.Lazy.Internal.ByteString) I did the full qualified because the first time I tried your suggestion I just "Control.Exception.Lifted" and I got the same error as I'm sharing below. playhaven.hs:51:19: Couldn't match expected type `IO b0' with actual type `GHandler sub0 master0 RepJson' In the expression: Thanks for being willing to help me with this. Bryce

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On 9/26/12 6:00 PM, Ertugrul Söylemez wrote:

Bryce Verdier wrote:

...

body <- L.try (simpleHttp "http://www.google.com") :: IO (Either L.SomeException Data.ByteString.Lazy.Internal.ByteString)

Almost right, but your type signature is lying. =)

Greets, Ertugrul

Thanks for your hint, with a fair amount of head bashing against a wall I was able to figure this out. At the end of day I got : body <- try (simpleHttp "http://www.google.com") :: GHandler PlayHaven PlayHaven (Either SomeException ByteString) But what I don't understand, is why do I have GHandler PlayHaven PlayHaven (Either SomeException ByteString) instead of IO (Either SomeException ByteString)? Thanks again, Bryce

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On 9/27/12 10:33 AM, Brent Yorgey wrote:

On Thu, Sep 27, 2012 at 10:01:25AM -0700, Bryce Verdier wrote:

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On 9/26/12 6:00 PM, Ertugrul Söylemez wrote:

...

Bryce Verdier wrote:

...

body <- L.try (simpleHttp "http://www.google.com") :: IO (Either L.SomeException Data.ByteString.Lazy.Internal.ByteString)

Almost right, but your type signature is lying. =)

Greets, Ertugrul Thanks for your hint, with a fair amount of head bashing against a wall I was able to figure this out. At the end of day I got :

body <- try (simpleHttp "http://www.google.com") :: GHandler PlayHaven PlayHaven (Either SomeException ByteString) Do you need a type signature there at all?

-Brent That is an awesome question. Originally I tried:

body <- try (simpleHttp "http://www.google.com") and I got this error: playhaven.hs:54:73: Ambiguous type variable `a0' in the constraints: (Show a0) arising from a use of `show' at playhaven.hs:54:73-76 (Exception a0) arising from a use of `try' at playhaven.hs:52:13-15 Probable fix: add a type signature that fixes these type variable(s) So I figured that adding the type signature would help with it. If you know of another way to make this work I would really like to hear about it. Thanks, Bryce

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On Thu, Sep 27, 2012 at 7:38 PM, Bryce Verdier wrote:

On 9/27/12 10:33 AM, Brent Yorgey wrote:

...

On Thu, Sep 27, 2012 at 10:01:25AM -0700, Bryce Verdier wrote:

...

On 9/26/12 6:00 PM, Ertugrul Söylemez wrote:

...

Bryce Verdier wrote:

body <- L.try (simpleHttp "http://www.google.com") :: IO (Either

...

L.SomeException Data.ByteString.Lazy.Internal.**ByteString)

Almost right, but your type signature is lying. =)

Greets, Ertugrul

Thanks for your hint, with a fair amount of head bashing against a wall I was able to figure this out. At the end of day I got :

body <- try (simpleHttp "http://www.google.com") :: GHandler PlayHaven PlayHaven (Either SomeException ByteString)

Do you need a type signature there at all?

-Brent

That is an awesome question. Originally I tried:

body <- try (simpleHttp "http://www.google.com")

this can be made to work by adding less stuff :

getGoogR = do body <- try (simpleHttp "http://www.google.com") case body of Left (SomeException _) -> jsonToRepJson $ object ["response" .= ( show "ERROR: NO DATA FOR ONE REASON OR ANOTHER")] Right val -> jsonToRepJson $ object ["response" .= (showDigest $ sha1 val)]

I think that should work... -- Jedaï

On 9/27/12 12:43 PM, Chaddaï Fouché wrote:

On Thu, Sep 27, 2012 at 9:25 PM, Chaddaï Fouché wrote:

...

...

body <- try (simpleHttp "http://www.google.com") case body of Left (SomeException _) -> jsonToRepJson $ object ["response" .= ( show "ERROR: NO DATA FOR ONE REASON OR ANOTHER")]

I think that should work...

Thank you for that Jedai! That looks MUCH MUCH cleaner than the :: GHandler ... type signature.

Since the signature was made necessary by the ambiguity on which type of exception you wished to catch with your "try", using (SomeException _) in your pattern match should make that clear. By the way, why are you show()ing a String ? The only thing that does is adding quotes around it and escaping some characters, shouldn't you just use :

...

Left (SomeException _) -> jsonToRepJson $ object ["response" .= "ERROR: NO DATA FOR ONE REASON OR ANOTHER"]

I was doing that because when I removed it, I got an error similar to this: Ambiguous type variable `a0' in the constraints: (Data.String.IsString a0) arising from the literal `"ERROR: "' at playhaven.hs:54:73-81 (aeson-0.6.0.2:Data.Aeson.Types.Class.ToJSON a0)

which I was able to remove by throwing a show in there. If you know of a better way I would love to know about it. Thanks again! Bryce

I think what he is asking is if try (from lifted) has type try :: (MonadBaseControlhttp://hackage.haskell.org/packages/archive/monad-control/0.3.1.4/doc/html/C... IOhttp://hackage.haskell.org/packages/archive/base/4.5.0.0/doc/html/System-IO....m, Exceptionhttp://hackage.haskell.org/packages/archive/base/4.5.0.0/doc/html/Control-Ex...e) => m a -> m ( Eitherhttp://hackage.haskell.org/packages/archive/base/4.5.0.0/doc/html/Data-Eithe...e a) and simpleHttp is simpleHttp "googe" :: IOhttp://hackage.haskell.org/packages/archive/base/4.6.0.0/doc/html/System-IO....( Resulthttp://hackage.haskell.org/packages/archive/HTTP/latest/doc/html/Network-Str...( Responsehttp://hackage.haskell.org/packages/archive/HTTP/latest/doc/html/Network-HTT...ty)) then how can the whole statement have try $ simpleHttp "goog" :: GHandler master sub (Either SomeException ByteString) when the m in both parts of try is the same, it should end up IO not GHandler master sub. So I don't understand why this would work, either. On Thu, Sep 27, 2012 at 1:33 PM, Brent Yorgey wrote:

On Thu, Sep 27, 2012 at 10:01:25AM -0700, Bryce Verdier wrote:

...

On 9/26/12 6:00 PM, Ertugrul Söylemez wrote:

...

Bryce Verdier wrote:

...

body <- L.try (simpleHttp "http://www.google.com") :: IO (Either L.SomeException Data.ByteString.Lazy.Internal.ByteString)

Almost right, but your type signature is lying. =)

Greets, Ertugrul

Thanks for your hint, with a fair amount of head bashing against a wall I was able to figure this out. At the end of day I got :

body <- try (simpleHttp "http://www.google.com") :: GHandler PlayHaven PlayHaven (Either SomeException ByteString)

Do you need a type signature there at all?

-Brent

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