I'd like to be able to do something like: import qualified Data.Massiv.Array (qualified map).
This gives error: parse error on input `map'.
Or better yet, import qualified Data.Massiv.Array (qualified map) as AM, so I also can access foo as either foo or AM.foo, unless foo == map, then I have to use AM.map. This is to avoid conflict with Prelude.map.
Write two imports and you can use map as AM.map and use other functions without AM..
import qualified Data.Massiv.Array as AM
import Data.Massiv.Array hiding (map)
I would like to use servant, in particular implement a literate haskell file. I cannot figure out how to use the literate haskell file. I've been searching for documentation but nothing helpful has come up.
So far I have named the file correctly with the extension .lhs and I have executed runhaskell filename.lhs. I am receiving the following error:
servantfinaltest.lhs line 150: unlit: No definitions in file (perhaps you forgot the '>'s?)
`unlit' failed in phase `Literate pre-processor'. (Exit code: 1)
This is my .lhs file below:
# Serving an API
Enough chit-chat about type-level combinators and representing an API as a
type. Can we have a webservice already?
## A first example
Equipped with some basic knowledge about the way we represent APIs, let's now
write our first webservice.
The source for this tutorial section is a literate haskell file, so first we
need to have some language extensions and imports:
``` haskell
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeOperators #-}
module Server where
import Prelude ()
import Prelude.Compat
import Control.Monad.Except
import Control.Monad.Reader
import Data.Aeson.Compat
import Data.Aeson.Types
import Data.Attoparsec.ByteString
import Data.ByteString (ByteString)
import Data.List
import Data.Maybe
import Data.String.Conversions
import Data.Time.Calendar
import GHC.Generics
import Lucid
import Network.HTTP.Media ((//), (/:))
import Network.Wai
import Network.Wai.Handler.Warp
import Servant
import System.Directory
import Text.Blaze
import Text.Blaze.Html.Renderer.Utf8
import qualified Data.Aeson.Parser
import qualified Text.Blaze.Html
```
**Important**: the `Servant` module comes from the **servant-server** package,
the one that lets us run webservers that implement a particular API type. It
reexports all the types from the **servant** package that let you declare API
types as well as everything you need to turn your request handlers into a
fully-fledged webserver. This means that in your applications, you can just add
**servant-server** as a dependency, import `Servant` and not worry about anything
else.
We will write a server that will serve the following API.
``` haskell
type UserAPI1 = "users" :> Get '[JSON] [User]
```
Here's what we would like to see when making a GET request to `/users`.
``` javascript
[ {"name": "Isaac Newton", "age": 372, "email": "isaac#newton.co.uk", "registration_date": "1683-03-01"}
, {"name": "Albert Einstein", "age": 136, "email": "ae#mc2.org", "registration_date": "1905-12-01"}
]
```
Now let's define our `User` data type and write some instances for it.
``` haskell
data User = User
{ name :: String
, age :: Int
, email :: String
, registration_date :: Day
} deriving (Eq, Show, Generic)
instance ToJSON User
```
Nothing funny going on here. But we now can define our list of two users.
``` haskell
users1 :: [User]
users1 =
[ User "Isaac Newton" 372 "isaac#newton.co.uk" (fromGregorian 1683 3 1)
, User "Albert Einstein" 136 "ae#mc2.org" (fromGregorian 1905 12 1)
]
```
Let's also write our API type.
``` haskell ignore
type UserAPI1 = "users" :> Get '[JSON] [User]
```
We can now take care of writing the actual webservice that will handle requests
to such an API. This one will be very simple, being reduced to just a single
endpoint. The type of the web application is determined by the API type,
through a *type family* named `Server`. (Type families are just functions that
take types as input and return types.) The `Server` type family will compute
the right type that a bunch of request handlers should have just from the
corresponding API type.
The first thing to know about the `Server` type family is that behind the
scenes it will drive the routing, letting you focus only on the business
logic. The second thing to know is that for each endpoint, your handlers will
by default run in the `Handler` monad. This is overridable very
easily, as explained near the end of this guide. Third thing, the type of the
value returned in that monad must be the same as the second argument of the
HTTP method combinator used for the corresponding endpoint. In our case, it
means we must provide a handler of type `Handler [User]`. Well,
we have a monad, let's just `return` our list:
``` haskell
server1 :: Server UserAPI1
server1 = return users1
```
That's it. Now we can turn `server` into an actual webserver using
[wai](http://hackage.haskell.org/package/wai) and
[warp](http://hackage.haskell.org/package/warp):
``` haskell
userAPI :: Proxy UserAPI1
userAPI = Proxy
-- 'serve' comes from servant and hands you a WAI Application,
-- which you can think of as an "abstract" web application,
-- not yet a webserver.
app1 :: Application
app1 = serve userAPI server1
```
The `userAPI` bit is, alas, boilerplate (we need it to guide type inference).
But that's about as much boilerplate as you get.
And we're done! Let's run our webservice on the port 8081.
``` haskell
main :: IO ()
main = run 8081 app1
```
First of all - if you have not written any haskell code - starting with servant and is I'd say quite ambitious - as it leverages several high level concepts/mechanisms provided by several language extensions like TypeFamilies and DataKinds ...
What you are writing is no literate haskell file - at least it violates the syntax as described here
I recommend either sticking to normal haskell files or reading the document I linked to first.
Here is a translation of your file into valid literate haskell:
# Serving an API
Enough chit-chat about type-level combinators and representing an API as a
type. Can we have a webservice already?
## A first example
Equipped with some basic knowledge about the way we represent APIs, let's now write our first webservice.
The source for this tutorial section is a literate haskell file, so first we need to have some language extensions and imports:
``` haskell
> {-# LANGUAGE DataKinds #-}
> {-# LANGUAGE DeriveGeneric #-}
> {-# LANGUAGE FlexibleInstances #-}
> {-# LANGUAGE GeneralizedNewtypeDeriving #-}
> {-# LANGUAGE MultiParamTypeClasses #-}
> {-# LANGUAGE OverloadedStrings #-}
> {-# LANGUAGE ScopedTypeVariables #-}
> {-# LANGUAGE TypeOperators #-}
> module Server where
> import Prelude ()
> import Prelude.Compat
> import Control.Monad.Except
> import Control.Monad.Reader
> import Data.Aeson.Compat
> import Data.Aeson.Types
> import Data.Attoparsec.ByteString
> import Data.ByteString (ByteString)
> import Data.List
> import Data.Maybe
> import Data.String.Conversions
> import Data.Time.Calendar
> import GHC.Generics
> import Lucid
> import Network.HTTP.Media ((//), (/:))
> import Network.Wai
> import Network.Wai.Handler.Warp
> import Servant
> import System.Directory
> import Text.Blaze
> import Text.Blaze.Html.Renderer.Utf8
> import qualified Data.Aeson.Parser
> import qualified Text.Blaze.Html
```
**Important**: the `Servant` module comes from the **servant-server** package, the one that lets us run webservers that implement a particular API type. It reexports all the types from the **servant** package that let you declare API types as well as everything you need to turn your request handlers into a fully-fledged webserver. This means that in your applications, you can just add **servant-server** as a dependency, import `Servant` and not worry about anything else.
We will write a server that will serve the following API.
``` haskell
> type UserAPI1 = "users" :> Get '[JSON] [User]
```
Here's what we would like to see when making a GET request to `/users`.
``` javascript
[ {"name": "Isaac Newton", "age": 372, "email": "isaac#newton.co.uk", "registration_date": "1683-03-01"}
, {"name": "Albert Einstein", "age": 136, "email": "ae#mc2.org", "registration_date": "1905-12-01"}
]
```
Now let's define our `User` data type and write some instances for it.
``` haskell
> data User = User
> { name :: String
> , age :: Int
> , email :: String
> , registration_date :: Day
> } deriving (Eq, Show, Generic)
> instance ToJSON User
```
Nothing funny going on here. But we now can define our list of two users.
``` haskell
> users1 :: [User]
> users1 =
> [ User "Isaac Newton" 372 "isaac#newton.co.uk" (fromGregorian 1683 3 1)
> , User "Albert Einstein" 136 "ae#mc2.org" (fromGregorian 1905 12 1)
> ]
```
Let's also write our API type.
``` haskell ignore
type UserAPI1 = "users" :> Get '[JSON] [User]
```
We can now take care of writing the actual webservice that will handle requests to such an API. This one will be very simple, being reduced to just a single endpoint. The type of the web application is determined by the API type, through a *type family* named `Server`. (Type families are just functions that take types as input and return types.) The `Server` type family will compute the right type that a bunch of request handlers should have just from the
corresponding API type.
The first thing to know about the `Server` type family is that behind the
scenes it will drive the routing, letting you focus only on the business
logic. The second thing to know is that for each endpoint, your handlers will by default run in the `Handler` monad. This is overridable very
easily, as explained near the end of this guide. Third thing, the type of the value returned in that monad must be the same as the second argument of the HTTP method combinator used for the corresponding endpoint. In our case, it means we must provide a handler of type `Handler [User]`. Well,
we have a monad, let's just `return` our list:
``` haskell
> server1 :: Server UserAPI1
> server1 = return users1
```
That's it. Now we can turn `server` into an actual webserver using
[wai](http://hackage.haskell.org/package/wai) and
[warp](http://hackage.haskell.org/package/warp):
``` haskell
> userAPI :: Proxy UserAPI1
> userAPI = Proxy
```
'serve' comes from servant and hands you a WAI Application,
which you can think of as an "abstract" web application,
not yet a webserver.
```haskell
> app1 :: Application
> app1 = serve userAPI server1
```
The `userAPI` bit is, alas, boilerplate (we need it to guide type inference).
But that's about as much boilerplate as you get.
And we're done! Let's run our webservice on the port 8081.
```haskell
> main :: IO ()
> main = run 8081 app1
```
I'm trying to understand how to create a GUI with GHCJS-DOM. I've been looking at the hello world example https://github.com/ghcjs/ghcjs-dom-hello, which is trivial. Adding new nodes is straightforward. What I can't do, and cannot work out from the library documentation (only signatures) is to add some events. For example add a new node to the body on a mouse click.
I wish to avoid using JS libraries like JQuery, because I want by GUI to be portable between GHC (webkit) and GHCJS.
Ultimately I'd like to be able to express a mouse event as a FRP Event, but I'll settle for one step at a time.
If anyone has any guidance I'd be most grateful. I've used haskell for a few years now, but this is my first venture into DOM.
You can get information about the DOM from a number of places including mozilla. Here is an example that adds an event handler for click events on the document body...
module Main (
main
) where
import Control.Applicative ((<$>))
import Control.Monad.Trans (liftIO)
import GHCJS.DOM
(enableInspector, webViewGetDomDocument, runWebGUI)
import GHCJS.DOM.Document (documentGetBody, documentCreateElement)
import GHCJS.DOM.HTMLElement (htmlElementSetInnerHTML, htmlElementSetInnerText)
import GHCJS.DOM.Element (elementOnclick)
import GHCJS.DOM.HTMLParagraphElement
(castToHTMLParagraphElement)
import GHCJS.DOM.Node (nodeAppendChild)
import GHCJS.DOM.EventM (mouseClientXY)
main = runWebGUI $ \ webView -> do
enableInspector webView
Just doc <- webViewGetDomDocument webView
Just body <- documentGetBody doc
htmlElementSetInnerHTML body "<h1>Hello World</h1>"
elementOnclick body $ do
(x, y) <- mouseClientXY
liftIO $ do
Just newParagraph <- fmap castToHTMLParagraphElement <$> documentCreateElement doc "p"
htmlElementSetInnerText newParagraph $ "Click " ++ show (x, y)
nodeAppendChild body (Just newParagraph)
return ()
return ()
How can I convert the internal value to a Data.Text.Text?
import qualified Data.Text as T
import qualified Data.Text.Lazy.IO as X
main = do
name <- X.readFile "someFile"
How can I convert the value in name to T.Text?
There's a function explicitly for that, Data.Text.Lazy.toStrict.
I suppose you're actually doing something else in between that requires reading as a lazy Text, otherwise, you should read as a strict Text directly of course.
I'm using the file-embed package thusly:
import qualified Data.ByteString as B
import qualified Data.ByteString.Internal as B (w2c)
import qualified Data.FileEmbed as E
initWindow = do
b <- Gtk.builderNew
let glade = map B.w2c $ B.unpack $ $(E.embedFile "window.glade") in
Gtk.builderAddFromString b glade
...
Is it possible to make cabal rebuild this file even when only the glade file changes?
Support for this will be/has been added in GHC 7.4/7.6. The problem is that the compiler doesn't allow TemplateHaskell splices to add file dependencies yet. See this ticket for more information.
When this change lands, you can use the following code to create a new embedFile' function:
import Data.FileEmbed
import Language.Haskell.TH.Syntax
import Language.Haskell.TH.Lib
embedFile' :: FilePath -> Q Exp
embedFile' path = do
qAddDependentFile path
embedFile path
This has to be in a separate module from where you use the TH function.