On Wed, Aug 01, 2007 at 01:48:07PM -0700, David Pollak wrote:

Howdy,

I'm considering building a desktop app using Haskell. The primary target for the app is Windows, but if it runs on Linux and Mac (Intel and PPC), that'd be a bonus. I've got a bunch of questions that hopefully folks can answer.

I use a Unix; treat my answers as thus qualified.

Well, before I start, you might well be asking "Gee David, you're a Scala kind of guy... I mean, you're the primary contributor to lift... why not use Scala?" Well, I'm looking to build something that compiles down to native code and has a smaller download (and runtime) footprint than the JVM offers. I've come to love functional programming and am taking the current side project as an opportunity to learn Haskell.

So... on to the questions:

- Can GHC generate stand-alone executables with all the dependencies linked in such that I can distribute the single file without worrying about including a bunch of DLLs/SOs? The answer seems to be yes, but I wanted to confirm.

Currently, GHC doesn't support generating shared libraries at all, so all you have to worry about is libc and friends, but that's usually pre-installled and some combination of -static -optl-static will fix it.

- How much of a distribution footprint is the Haskell runtime? If I have a "Hello World" app, roughly how big will the EXE be (if one includes the JRE in the runtime, a Java/Scala program has a minimum footprint of 20M... that's big.)

About 500kb.

- Same goes for the runtime... I've looked at the stats on the Language Shootout home page and these look encouraging, but I wanted to see if the reasonable footprint is a reality.

It's pretty reasonable. I don't have exact numbers due to the vagarities of Linux demand loading, but Don reports that xmonad and dwm use very similar amounts of memory, ie whatever RTS overhead exists is swamped by the 2MB runtime footprint of Xlib.

- How real/solid/stable is the wxHaskell widgets package? Is it being well maintained? Is there (okay... this is pie in the sky) an GUI Builder for it? - How are the Windows/COM bindings in Haskell... would it be possible to, for example, embed an IE Browser COM control in a a wxHaskell window?

Unknown.

- I found a package to do HTTP requests in Haskell but it does not seem to support HTTPS. Is there an HTTPS client package for Haskell?

Maybe soon; the current HTTP package is widely acknowledged as being in dire need of an overhaul, and Mietek Bak is doing exactly that as part of the SoC.

- How are Strings internally represented? Are they single byte or multi-byte characters? How easy it is to translate to/from internal representation to UTF-8?

A cons-list of characters, so 12 bytes per character. Characters are internally memoized only if they are smaller than 256, so add 8 bytes for every non-latin1 character. Double the numbers for a 64-bit system. They can represent full Unicode, but there's none of the traditional "multi byte" stuff - one cell is one character. Quite easy, Mertens et al recently released a utf8-string library that should make it completely automatic. (I haven't used it yet)

- How's the XML support? Will the XML parser handle non-Latin characters and properly encode stuff? Does XML get parsed down into easily mappable/filterable collections?

We have no less than three XML parsers, none of which I have experience using.

- Is there support for SHA256 (I saw an SSLeay package which had support for a lot of stuff, but not SHA256)?

Probably not.

- I understand that Haskell has "a better approach" to parallelizing tasks, but I have not seen much about the actual manifestation of this... would someone be so kind as to give me a pointer?

http://www.macs.hw.ac.uk/~dsg/gph/papers/abstracts/strategies.html We also have ordinary threads with basic standard concurrency abstractions, Control.Concurrent.*.

- On a related note, I have become a fan (via Scala) of Erlang-style Actors and asynchronous message passing. Are there any similar packages for Haskell?

Sure. Control.Concurrent.Chan gives asynchronous message passing.

- I tend to do most of my coding in either Emacs or Eclipse... how's the Haskell support in either? Is there a preferred editor (I don't mean to start any wars here... :-)

Emacs and vi both have native support for Haskell. Emacs additionally has basic integration with the interactive environments (Reload buffer, stuff like that) and passable auto-indenting (hard to do right in a language with significant whitespace); B. Schmidt's "shim" package provides more, like automatic error highlighting. Eclipse supports Haskell via an addon-package "EclipseFP", I've only heard about it never used it.

- Are there any production Haskell-based desktop apps of note?

Anyway... sorry for the long list of questions. I look forward to hearing from you all and learning more about Haskell.

Stefan

On Wed, 2007-08-01 at 13:48 -0700, David Pollak wrote:

So... on to the questions:

First of all I recommend you check out these resources: The standard libraries: http://haskell.org/ghc/docs/latest/html/libraries/ A large collection of other libraries: http://hackage.haskell.org/ Another directory of apps and libraries, many of which are not yet available through hackage: http://haskell.org/haskellwiki/Applications_and_libraries

* Can GHC generate stand-alone executables with all the dependencies linked in such that I can distribute the single file without worrying about including a bunch of DLLs/SOs? The answer seems to be yes, but I wanted to confirm.

Yes, but the same is not true of any C dlls you link to, eg GUI libs like gtk or wx.

* How much of a distribution footprint is the Haskell runtime? If I have a "Hello World" app, roughly how big will the EXE be (if one includes the JRE in the runtime, a Java/Scala program has a minimum footprint of 20M... that's big.)

Statically linked hello world is 470K on my amd64 linux box. An equivalent GUI hello world with Gtk2Hs is 540K. These are still dynamically liked to libc and libgmp.

* Same goes for the runtime... I've looked at the stats on the Language Shootout home page and these look encouraging, but I wanted to see if the reasonable footprint is a reality.

Not sure what you're asking here. The ghc rts is linked into the program.

* How real/solid/stable is the wxHaskell widgets package? Is it being well maintained? Is there (okay... this is pie in the sky) an GUI Builder for it?

Perhaps someone who uses wxHaskell can help you with that. I help maintain Gtk2Hs so can tell you about that... Gtk2Hs is well maintained imho :-) We do releases roughly every 6 months. The last one was a couple weeks ago. It has an installer for Windows and it's included in several other platforms like debian, fedora, gentoo, freebsd and macports. The glade GUI builder can be used with Gtk2Hs on all platforms.

* How are the Windows/COM bindings in Haskell... would it be possible to, for example, embed an IE Browser COM control in a a wxHaskell window?

There is a COM tool, not sure about embedding IE. Gtk2Hs supports embedding the mozilla rendering engine, though not on Windows at the moment. HDirect has not seen much maintenance but apparently there is an updated version that was used in VisualHaskell. Perhaps someone else can tell you more about HDirect, I'm not especially familiar with it. http://www.haskell.org/hdirect/ http://www.haskell.org/visualhaskell/

* I found a package to do HTTP requests in Haskell but it does not seem to support HTTPS. Is there an HTTPS client package for Haskell?

There's work on a libcurl binding going on at the moment.

* How are Strings internally represented? Are they single byte or multi-byte characters? How easy it is to translate to/from internal representation to UTF-8?

Strings are represented as ordinary Haskell lists of Unicode code points. There are functions available for converting to and from byte sequences in UTF8 and other encodings (though not in the base packages at the moment). Both Gtk2Hs and wxHaskell support Unicode.

* How's the XML support? Will the XML parser handle non-Latin characters and properly encode stuff? Does XML get parsed down into easily mappable/filterable collections?

There are 2 major xml packages, HaXml and HXT. You can download them and find their documentation on http://hackage.haskell.org/

* Is there support for SHA256 (I saw an SSLeay package which had support for a lot of stuff, but not SHA256)?

The Crypto package supports SHA1.

* I understand that Haskell has "a better approach" to parallelizing tasks, but I have not seen much about the actual manifestation of this... would someone be so kind as to give me a pointer?

Look for Haskell's lightweight threads, STM and parallel strategies: Control.Concurrent Control.Concurrent.STM Control.Parallel.Strategies

* On a related note, I have become a fan (via Scala) of Erlang-style Actors and asynchronous message passing. Are there any similar packages for Haskell?

Not so far as I know, though the concurrency library supports channels so you can use a pattern where a thread reads messages from a channel and post's messages to other channels.

* I tend to do most of my coding in either Emacs or Eclipse... how's the Haskell support in either? Is there a preferred editor (I don't mean to start any wars here... :-)

Emacs, vim, nedit, gedit and others support Haskell syntax highlighting. Emacs has some additional ghci integration mode. There's a project to add Haskell support to Eclipse, though I'm not sure how mature it is.

* Are there any production Haskell-based desktop apps of note?

xmonad, an X11 window manager VisualHaskell, a Haskell extension to VisualStudio There are a number of programs that use Gtk2Hs or wxHaskell which you can find linked from their websites including: dazzle, http://wxhaskell.sourceforge.net/applications.html pivotal, http://www.cs.kent.ac.uk/projects/pivotal/ himerge, http://fmap.us/himerge.html HRay, http://trappist.elis.ugent.be/~kehoste/Haskell/HRay/ Duncan

My answers apply to Windows/GHC. David Pollak wrote:

* Can GHC generate stand-alone executables with all the dependencies linked in such that I can distribute the single file without worrying about including a bunch of DLLs/SOs? The answer seems to be yes, but I wanted to confirm.

Yes.

* How much of a distribution footprint is the Haskell runtime? If I have a "Hello World" app, roughly how big will the EXE be (if one includes the JRE in the runtime, a Java/Scala program has a minimum footprint of 20M... that's big.)

A hello world application executable on Windows/GHC 6.6.1 is 592,385 bytes. But the size grows very quickly to 1-2 MB when you start including the basic libraries.

* Same goes for the runtime... I've looked at the stats on the Language Shootout home page and these look encouraging, but I wanted to see if the reasonable footprint is a reality.

The memory footprint of a well-written Haskell program seems to be very small. I once wrote a text parser that only used a maximum of 2 MB of memory while processing an infinite stream. This is much less than the minimum footprint of the JVM. One reason for this is that the GHC garbage collector officially kicks ass. However, it is exceedingly easy to write memory-leaking programs in Haskell. Fortunately memory leaks usually manifest themselves as a program crash (stack overflow) or very high heap usage (easy to monitor in task explorer). In any case, the memory usage is pretty easy to monitor with GHC's built-in profiling facilities. Now fixing Haskell memory leaks... a completely different story. It's nothing short of black magic. Performing the simplest program optimizations and fixing the simplest of memory leaks generally requires a level of gurudom that is not even possible to achieve just with Java/C/C++ programming. Fixing a Haskell program usually involves performing a couple of sacred rites, sacrifices, voodoo rituals (you can consult your preferred deity, it doesn't matter). When that doesn't help, approach the Gurus of this forun, place the ritual Offering and plead for help. If they are satisfied with you, they might, just might, throw you a scrap of wisdom from their infinite mental capacity, which upon receiving will shock and humble you for life. Usually it sounds like this: "Here's a one line fold that replaces your entire program and doesn't have the memory leak."

* I tend to do most of my coding in either Emacs or Eclipse... how's the Haskell support in either? Is there a preferred editor (I don't mean to start any wars here... :-)

Yes, there's a plugin for Eclipse. It's actually slightly better than the Scala plugin you're probably familiar with :) There's also a good syntax highlighting file for jEdit. Niko