[Haskell-cafe] ANN (2 Libs) -- hvac 0.1b,
a lightweight web framework and HStringTemplate 0.3
tphyahoo at gmail.com
Tue Jun 3 13:08:19 EDT 2008
I just tried out hvac. I was trying to run the hvac examples
after following the readme in the samples directory.
sudo lighttpd -D -f lh.conf
[sudo] password for thartman:
2008-06-03 09:30:02: (log.c.75) server started
so that's okay, but
in firefox attempted to open a binary file "1".
Same result for http://localhost:3000/hvac-board
I don't know if this is an hvac issue or a fastcgi issue (seems more
likely) but any
2008/3/22 Sterling Clover <s.clover at gmail.com>:
> 1) hvac 0.1b: transactional, declarative framework for lightweight web
> 2) HStringTemplate 0.3
> 1) hvac 0.1b
> hvac (short for http view and controller) has been my project for the last
> little while, and is finally in a fairly usable state, so I'm opening up the
> repo (darcs get http://community.haskell.org/~sclv/hvac/) for folks to play
> with and to get some feedback. While not quite yet ready for hackage, the
> package as provided should be fully cabal installable. Documentation is
> available at http://community.haskell.org/~sclv/hvac/html_docs/hvac/
> The aim of hvac is to provide an environment that makes the creation of
> lightweight fastcgi based web applications as simple as possible, with an
> emphasis on concise, declarative style code, correct concurrent
> transactional logic, and transparency in adding caching combinators.
> There are two included example programs, naturally neither of which is
> feature complete. They share a common login module of about 50 lines of
> code, excluding imports, templates, and database schema.
> The first program is a classic, greenspun-style message board with basic
> login functionality. It totals roughly 40 lines and tends to use just under
> 4mb of resident memory on my system.
> The second is a wiki based on Pandoc and the PandocWiki code. The code
> totals roughly 30 lines (rendering borrowed from PandocWiki aside) and uses
> about 5mb of memory.
> hvac processes all requests in the STM monad, with some bells attached to
> properly interleave STM with session, database and filesystem operations
> such that they all conceptually occur together in a single transaction per
> request. Currently it is only fully tested with sqlite, but it should
> operate, modulo a few tweaks, with any database accessible via HDBC.
> hvac is particularly designed to use the HStringTemplate library as an
> output layer, in a simple declarative fashion. As the StringTemplate grammar
> is explicitly sub-turing, this ensures a clean separation of program logic
> from presentation, while providing a nonetheless fairly powerful language to
> express typical display tasks.
> The included cache combinators, still experimental, should allow a simple
> and fine-grained control over the level of caching of various disk-bound
> operations. Phantom types are used to ensure that no functions that modify
> state may be cached.
> To give a flavor of hvac code, the following is the complete (twenty lines!)
> source of the wiki controller (due to sql statements, some lines are rather
> wikiController tmpl =
> h |/ "login" *> login_plug tmpl
> (h |/ "wiki" |\\ \pageName -> h |// "POST" *>
> withValidation [ ("contents", return) ]
> (\ [contents] -> do
> pageId <- selectVal "id from pages where name=?" [toSql
> maybe (addErrors [("Login","must be logged in.")] >> continue)
> (\user -> case fromSql pageId of
> Just (_::Int) ->
> execStat "insert into
> page_hist(pageId,contents,author) values(?,?,?)" [pageId, toSql contents,
> toSql . userName $ user]
> Nothing -> do
> execStat "insert into pages(name,locked)
> values(?,?)" [toSql pageName, toSql (0::Int)]
> pid <- selectVal "max(id) from pages" 
> execStat "insert into
> page_hist(pageId,contents,author) values(?,?,?)" [pid, toSql contents, toSql
> . userName $ user]) =<< getSes
> <|> do
> pageId <- selectVal "id from pages where name=?" [toSql pageName]
> (join $ renderf (tmpl "showPage") ("pageName", pageName)
> <$> "pageContents" |= selectRow "* from page_hist where
> pageId=? order by time desc limit 1" [pageId] ))
> <|> (redirect . ( ++ "/wiki/Index") =<< scriptName)
> Future directions for work on hvac include: Stress testing for correctness
> of transactional logic and benchmarks. Exploration of various efficiency
> tweaks. Unit tests. Further development of the cache combinator API.
> Improvement of the example apps and addition of a few others (a blog maybe).
> Expansion of the library of validator functions. Exploration of transferring
> hvac to the standard FastCGI bindings (currently it uses a custom modified
> version to work properly with STM). Improvement of the database layer,
> particularly with regards to common paging functions. Creation of a set of
> simple combinators for generating CRUD (create read update delete) pages.
> Creation of a minimal set of standard templates (maybe).
> 2) HStringTemplate 0.3.1
> This release of HStringTemplate (up now at Hackage) fixes a number of bugs
> pointed out to me by its small but growing user base (thanks, cinema,
> elliottt!) ranging from the minor (a particular two-level iteration pattern
> wasn't working properly) to the truly irritating (poor handling of file
> groups). It's still unfortunately skimpy on the docs, outside of the
> haddocks and the main StringTemplate grammar documentation at
> http://www.stringtemplate.org (although the examples from hvac should also
> prove helpful). However, it does have a set of very nice and handy new
> features for development.
> * renderf, a function similar in spirit to printf, that takes an arbitrary
> number of heterogeneous (String, value) tuples as arguments. This should cut
> down considerably on long setAttribute chains. Additionally, with custom
> instances (not, I'll grant, trivial to write) it can be used to
> declaratively chain together strings of attribute retrieval functions in
> arbitrary monads, as in the above code example from hvac.
> * dumpAttribs, a function/template that prints out the tree of the entire
> attribute environment a template is operating in -- extremely handy for
> * nullGroup, also for use in development, a simple way to display more
> information about templates that can't be found. Error messages in
> usafeVolatileDirectoryGroup have also been significantly improved.
> * getStringTemplate', a version of getStringTemplate guaranteed not to be
> inlined. While the optimizer will still sometimes rearrange code such that a
> volatile group is not updated properly, this at least helps remedy the
> situation (I think).
> * Some minor changes: For grammar reasons, dots have been removed from
> template names -- however, underscores and slashes are now available.
> Additionally, there's a much improved logic for which aspects of a local
> environment are overridden and preserved when a template is called from
> For both of these libraries, patches, comments, bug reports, requests, and
> of course contributions more than welcome!
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
More information about the Haskell-Cafe