Dynamic Loading of Haskell Code!

Gilberto Melfe

21 Feb 2014 21 Feb '14

11:25 a.m.

Hi there All! I would like to ask: Is it possible for a Haskell program to load code while it's running, in order for it to facilitate the implementation of Plugins? (like it's possible in Perl or Python) Can someone enlighten me, please? Thank You Gilberto

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Oliver Charles

21 Feb 21 Feb

11:54 a.m.

Gilberto Melfe writes:

...

Hi there All!

I would like to ask: Is it possible for a Haskell program to load code while it's running, in order for it to facilitate the implementation of Plugins? (like it's possible in Perl or Python)

One possible solution is the Haskell `hint` library: http://hackage.haskell.org/package/hint This uses the GHC API to allow you to compile strings into Haskell functions at runtime. This is a lot like `eval` in other languages. - ocharles

Brandon Allbery

11:59 a.m.

On Fri, Feb 21, 2014 at 11:25 AM, Gilberto Melfe wrote:

...

I would like to ask: Is it possible for a Haskell program to load code while it's running, in order for it to facilitate the implementation of Plugins? (like it's possible in Perl or Python)

Can someone enlighten me, please?

There's a plugins package on Hackage for this, but it's something of a pain to use. The whole notion of plugins is kinda at cross-purposes with static type checking. -- brandon s allbery kf8nh sine nomine associates allbery.b@gmail.com ballbery@sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net

Jeremy Shaw

3:12 p.m.

The plugins package is a dying a slow death anyway. (I'm the current maintainer). The GHC api, with a little bit of glue, seems to replace everything that current plugins package does -- and better too. You are correct that loading plugins and static typing are a bit at odds. If you loading things at runtime, then you have to be willing to accept that some errors will appear at runtime. I have developed a generic 'web-plugins' package that supports the loading of plugins into a running application. The dynamic loading feature is only proof-of-concept at the moment. But it shows one system for creating a plugin system, http://hackage.haskell.org/package/web-plugins-0.2.5/docs/Web-Plugins-Core.h... I am working on a independent library which adds extra wrappers around the ghc-api to us fsnotify to watch files and automatically recompile+reload, or to use cabal to fetch, build, and load plugin libraries from hackage into a running application. It's not a high priority at the moment though. I'd be happy to put the current code on github -- I just need a name. I'm not to fond of the name 'plugins' because it is a bit more general purpose than that and also doesn't directly provide plugins support -- just the tools need to create a plugins framework. - jeremy On Fri, Feb 21, 2014 at 10:59 AM, Brandon Allbery wrote:

...

On Fri, Feb 21, 2014 at 11:25 AM, Gilberto Melfe wrote:

...
I would like to ask: Is it possible for a Haskell program to load code while it's running, in order for it to facilitate the implementation of Plugins? (like it's possible in Perl or Python)

Can someone enlighten me, please?

There's a plugins package on Hackage for this, but it's something of a pain to use. The whole notion of plugins is kinda at cross-purposes with static type checking.

-- brandon s allbery kf8nh sine nomine associates allbery.b@gmail.com ballbery@sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net

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Brandon Allbery
Gilberto Melfe
Jeremy Shaw
Oliver Charles