[web-devel] Happstack Irregular News Issue #2

Jeremy Shaw jeremy at n-heptane.com
Mon Jul 2 18:45:02 CEST 2012


I pleased to announce that Happstack Irregular News Issue #2 is now
available. You can view it online at:


Or continue reading the rest of this message.

Happstack Irregular News Issue #2

Hello! It is I, your editor Jeremy Shaw. I am pleased to bring you
Happstack Irregular News Issue #2. Some exciting things have happened
since the last issue!


The biggest news since the last issue is the release of clckwrks:


clckwrks is a Haskell-based blog and CMS framework with support for
editing pages via the browser plus downloadable themes and plugins.

clckwrks is now powering happstack.com and clckwrks.com.

We are currently focusing on making the clckwrks blogging portion
solid. We have moved the official Happstack blog to clckwrks in order
to encourage us to make it better :)

If you want to help out, you can [browse our bug
list](http://www.clckwrks.com/B/Timeline) and find something to take
action on. We are more than happy to provide guidance and other


The other new big release was
[reform](http://www.happstack.com/C/ViewPage/11). `reform` is a form
generation library that continues in the footsteps of `formlets` and
`digestive-functors <= 0.2`. `digestive-functors 0.3` has gone off to
explore a different direction, and we wanted to continue pushing the
development in this direction. There are still many ideas we can share
between the two libraries. Two changes we want to make in the next
release include:

  1. switch to `Bifunctors` package instead of homebrewed
  `IndexedApplicative` (thanks to Leonid Onokhov for pointing that
  out). (Another alternative might be `index-core`, though it does not
  yet export the `Applicative` instances).

  2. consider using a `Free Applicative` / `Operational Applicative` for
  implementing the `reform` applicative instances. `digestive functors
  0.3` does something like this and Jasper Van der Jeugt said it was
  very beneficial and we should try it in `reform` as well.


Dag Odenhall has released `happstack-yui`, which makes it easy to use
YUI with Happstack. According the YUI website:

  "YUI is a free, open source JavaScript and CSS framework for
building richly interactive web applications."


[YUI website](http://yuilibrary.com/)


Niklas Broberg and I (Jeremy Shaw) did some work on HSX. It now builds
with GHC 7.4 and we also fixed some hidden bugs in
`HSX.Transform`. One thing we have been experimenting with is a
`QuasiQuoter` for HSX. A demo version can be found here:

    darcs get http://src.seereason.com/hsx-qq/

The QQ provides an alternative to the `trhsx` preprocessor and
allows you to write things like:

    html :: (XMLGenerator m) => XMLGenT m (XMLType m)
    html = [hsx| <p class="foo"><% map toUpper "hello, world!"  %></p> |]

This should be included in the next release of HSX.

The next release of HSX will also contain a major refactoring of the
packages. Mostly we are just planning to move modules into different
packages and divide things up differently. One major benefit of the
new arrangement is that you will no longer be required to install
`HJavaScript` and `HJScript` even though you probably never use them.

Other Minor Fixes

 * changed types in `happstack-lite` so that `serveFile` and `asContentType`
   work better together, and added `guessContentType`, `MimeMap`, `mimeType`

 * patched `happstack-jmacro` to work with older versions of `template haskell`

 * tweaks to `ixset.cabal` so that it does not require the latest
`Cabal` to build

acid-state and hackage2

I have started research into why hackage2 requires so much RAM to
run. I will be blogging about that separately. I do expect that we can
substantially reduce that amount of RAM it requires. So far I have
uncovered two minor issues:

 1. it turns out that `mapM Lazy.readFile fileList` returns the file
 contents lazily but opens all the files immediately. This means you
 can run out of file descriptors if you have a lot of checkpoints or
 event files. A patch has been submitted for `acid-state` and it will
 be fixed in the next release.

 2. `acid-state` reads the entire checkpoint file into RAM before
 decoding it. There are a couple places in the code that cause this to
 happen. The first place is in `cereal`. The `getLazyByteString`
 function does return a lazy `ByteString`.. but it does it by first
 reading a strict `ByteString` of the required length and then
 converting it into a lazy `ByteString`. Changing the behavior of
 `getLazyByteString` is actually quite difficult, as `cereal` was
 designed to allow for value-level error handling, instead of throwing
 async exceptions.

 We can probably work around this by using `runGetState` to get
 one-chunk at a time and build the lazy `ByteString` that way. That
 might actually be a lot less hackish than it sounds at first, because
 it allows us to explicity detect and handle failure cases and control
 how much and when things are read into RAM. Though, at that point, it
 starts to feel a bit like enumerators/iteratee/etc. Perhaps we will
 switch to `pipes` at some point in time. `pipes` provides streaming for
 pure (non-IO) values -- which is probably what we want here.


Evan Czaplicki has been doing a ton of work on ELM recently. As
described on the [ELM Language Homepage](http://elm-lang.org/):

  "Elm is a type-safe, functional reactive language that compiles to
HTML, CSS, and JavaScript."

It is easy to use ELM with Happstack -- no special support is
required. (i.e., we do not need `happstack-elm`). Vincent Ambo has
created a simple demo here:

[elm-happstack demo](https://github.com/tazjin/Elm/tree/master/Examples/elm-happstack)

web-routes + Hamlet

Vincent also wrote a nice blog post showing how to combine `web-routes`
(type-safe URL routing) with `Hamlet` (a `QuasiQuoter` for generating
`blaze-html` from HTML-like syntax):

[Best of both worlds: Using Hamlet and web-routes with

quasi-quoter for language-css

`JMacro` is great for creating JavaScript, but we still have a hole
when it comes to generating CSS. The
library already contains combinators and a syntax ADT for CSS3.

If it had a parser, then we could also create a syntax-checking
`[css| |]` `QuasiQuoter`.

I have discussed the idea with Anton Kholomiov, and he is interested
-- but we could use some one else to help write the parser. If you
love writing parsers, this should be a fun little project.

happstack.com theme

Finally, if you could suggest one thing that would make the
happstack.com website nicer that would be awesome. There are four
things we already plan to change:

 1. use black on white text instead of gray on white

 2. fix the paragraph width so that paragraphs are around 45em wide.

 3. fix the grid alignment so that things are properly aligned to the

 4. add more dates to the pages so that it clear that the site and
 project is still active

If you have other suggestions, we would love to hear them! If you want
to hack on the theme directly, that is even better!

Until next time, happy hacking.

 - Jeremy Shaw

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