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Today's Topics:
1. Re: Recommended DB layer? (harry)
2. Re: Recommended DB layer? (Felipe Almeida Lessa)
3. Re: Reform and blaze: trouble with example code (Jeremy Shaw)
----------------------------------------------------------------------
Message: 1
Date: Mon, 17 Jun 2013 13:56:00 +0000 (UTC)
From: harry <[email protected]>
Subject: Re: [Haskell-beginners] Recommended DB layer?
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
Jeremy Shaw <jeremy <at> n-heptane.com> writes:
> For example, I believe that at one point in time (no idea about right
now), persistent could not do SQL-level joins -- because not all backends
could support joins..
I don't know how persistent is implemented, but the usual solution to a
problem like that is that the capable backends will implement joins in SQL,
while the others fake it in code.
------------------------------
Message: 2
Date: Mon, 17 Jun 2013 13:00:16 -0300
From: Felipe Almeida Lessa <[email protected]>
Subject: Re: [Haskell-beginners] Recommended DB layer?
To: beginners <[email protected]>
Message-ID:
<CANd=ogekdcjg3wr4sbejok9sw4qfdg40vliozysagk1ux-1...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
On Mon, Jun 17, 2013 at 6:36 AM, Erik de Castro Lopo
<[email protected]> wrote:
>> If persistent aims to be able to target wildly different backends, some of
>> which are not even SQL based, then it seems like it would hard for it to
>> also have optimal performance.
>
> It is my understanding that esqueleto only supports SQL databases
That's correct. Esqueleto is, and always will be, SQL-only. Its goal
is to be as close to SQL as possible.
Cheers,
--
Felipe.
------------------------------
Message: 3
Date: Tue, 18 Jun 2013 00:17:29 -0500
From: Jeremy Shaw <[email protected]>
Subject: Re: [Haskell-beginners] Reform and blaze: trouble with
example code
To: Adrian May <[email protected]>
Cc: Jasper Van der Jeugt <[email protected]>,
"[email protected]" <[email protected]>
Message-ID:
<cage_jkboizsey+zeyyezk+f9hyhfwew64kxycy-vqgdtoop...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
Hello,
label has the type:
label :: (Monad m, ToMarkup children) => children -> Form m input error
Html () ()
Meaning the argument to 'label' can be anything which can be embedded as
markup. Unfortunately, when you use OverloadedStrings and write:
label "username: "
It doesn't know if it should treat "username: " as a String value or an
Html value -- as both have IsString instances. You can fix it by typing:
label ("username: " :: String)
So that it knows. That is pretty annoying, and so we should probably have a
function like:
labelString :: (Monad m) => String -> Form m input error Html () ()
which is not ambiguous, and you can do:
labelString "username: "
I believe I have added that to the reform-hsp library, but not reform-blaze.
In your second attempt, you imported the functions from .Common. But
inputtext takes an extra parameter there:
inputText ::
(Monad<http://hackage.haskell.org/packages/archive/base/4.6.0.1/doc/html/Control-Monad.html#t:Monad>
m,
FormError<http://hackage.haskell.org/packages/archive/reform/0.1.2/doc/html/Text-Reform-Backend.html#t:FormError>
error,
ToValue<http://hackage.haskell.org/packages/archive/blaze-markup/0.5.1.4/doc/html/Text-Blaze.html#t:ToValue>
text)
=> (input ->
Either<http://hackage.haskell.org/packages/archive/base/4.6.0.1/doc/html/Data-Either.html#t:Either>
error
text) -> text ->
Form<http://hackage.haskell.org/packages/archive/reform/0.1.2/doc/html/Text-Reform-Core.html#t:Form>
m
input error
Html<http://hackage.haskell.org/packages/archive/blaze-html/0.6.0.0/doc/html/Text-Blaze-Html.html#t:Html>
()
text
The .Common module is really only for common code that is shared between
.String, .Text, and whatever may come in the future. It should have a
comment at the top explaining its purpose. Sorry about that.
- jeremy
On Sat, Jun 15, 2013 at 4:19 AM, Adrian May
<[email protected]>wrote:
> Hi All,
>
> I'm trying to get this example working:
>
>
> http://patch-tag.com/r/stepcut/reform/snapshot/current/content/pretty/examples/BlazeMain.hs
>
> It emitted what I took to be bitrot about ToHtml having apparently been
> generallised to ToMarkup and similar stuff, so I banged it into this form:
>
> {-# LANGUAGE FlexibleContexts, FlexibleInstances, TypeFamilies,
> OverloadedStrings #-}
> module Main where
>
> import Control.Applicative.Indexed
> import Control.Monad
> import qualified Data.ByteString.Char8 as C
> * import Text.Blaze *
> import qualified Text.Blaze.Html5 as H
> import qualified Text.Blaze.Html5.Attributes as A
> import Text.Blaze.Renderer.Utf8 (renderHtml)
> import Text.Reform
> * --import Text.Reform.Blaze.Common*
> * --import Text.Reform.Blaze.Text*
> * import Text.Reform.Blaze.String*
> import Text.Reform.Happstack
> import Happstack.Server
> import SharedForm
>
> instance *ToMarkup* (DemoFormError [Input]) where
> *toMarkup* InvalidEmail = "Email address must contain a @."
> *toMarkup* InvalidUsername = "Username must not be blank."
> *toMarkup* (CommonError (InputMissing fid)) = H.toHtml $
> "Internal Error. Input missing: " ++ show fid
> *toMarkup* (CommonError (NoStringFound input)) = H.toHtml $
> "Internal Error. Could not extract a String from: " ++ show input
> *toMarkup* (CommonError (MultiStringsFound input)) = H.toHtml $
> "Internal Error. Found more than one String in: " ++ show input
>
> usernameForm :: (Monad m, FormInput input, *ToMarkup* (DemoFormError
> input)) =>
> String
> -> Form m input (DemoFormError input) *Markup* NotNull Username
> usernameForm initialValue =
> ( *label "username: " ++>* (Username <<$>> inputText initialValue
> `prove` (notNullProof InvalidUsername)))
> {-
> usernameForm :: (Monad m, FormInput input, ToMarkup (DemoFormError
> input)) =>
> String
> -> Form m input (DemoFormError input) Markup NotNull Username
> usernameForm initialValue =
> errorList ++> (*label "username: " ++> *(Username <<$>> inputText
> initialValue `prove` (notNullProof InvalidUsername)))
> -}
> blazeResponse :: *Markup* -> Response
> blazeResponse html = toResponseBS (C.pack "text/html;charset=UTF-8") $
> renderHtml html
>
> blazeForm :: *Markup* -> *Markup*
> blazeForm html =
> H.form ! A.action "/"
> ! A.method "POST"
> ! A.enctype "multipart/form-data" $
> do html
> H.input ! A.type_ "submit"
>
> formHandler :: (*ToMarkup* error, Show a) => Form (ServerPartT IO)
> [Input] error *Markup* proof a -> ServerPart Response
> formHandler form =
> msum [ do method GET
> html <- viewForm "user" form
> ok $ blazeResponse $ blazeForm html
>
> , do method POST
> r <- eitherForm environment "user" form
> case r of
> (Right a) -> ok $ toResponse $ show a
> (Left view) ->
> ok $ blazeResponse $ blazeForm view
>
> ]
>
> main :: IO ()
> main =
> do let form = usernameForm ""
> simpleHTTP nullConf $ do decodeBody (defaultBodyPolicy "/tmp" 0 10000
> 10000)
> formHandler form
>
>
> where *italics* indicate the bits I changed, but now I'm stumped by the *
> bold* bit barfing with:
>
> Taser.hs:30:13:
> Ambiguous type variable `children0' in the constraints:
> (Data.String.IsString children0)
> arising from the literal `"username: "' at Taser.hs:30:13-24
> (ToMarkup children0)
> arising from a use of `label' at Taser.hs:30:7-11
> Probable fix: add a type signature that fixes these type variable(s)
> In the first argument of `label', namely `"username: "'
> In the first argument of `(++>)', namely `label "username: "'
> In the expression:
> (label "username: "
> ++>
> (Username
> <<$>>
> inputText initialValue `prove` (notNullProof InvalidUsername)))
>
> If I take out label "username: " ++>, then it all works fine, except I
> don't have a label. I also tried putting the label inside the Username
> constructor with the same result.
>
> I have the following versions installed:
>
> * blaze-markup (library)
> Versions installed: 0.5.1.5
> * blaze-html (library)
> Versions installed: 0.6.1.1
> * reform (library)
> Versions installed: 0.1.2
> * reform-blaze (library)
> Versions installed: 0.1.2
> The Glorious Glasgow Haskell Compilation System, version 7.4.2
>
> Perhaps the markup thing is what broke it, but I can't see ToHtml in any
> of those modules.
>
> Thanks in advance,
> Adrian.
>
>
>
>
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