[Haskell-cafe] Dynamically find out instances of classes (pluginsystem for haskell)

[Bayley, Alistair]

> From: haskell-cafe-bounces at haskell.org 
> [mailto:haskell-cafe-bounces at haskell.org] On Behalf Of 
> Radoslaw Grzanka
> 
> Hi,
>   Is there any plugin system for haskell? For example, in Java, I can
> load all compiled classes from given directory, check their interfaces
> and run some methods through reflection etc. Is it possible in
> haskell, to load modules from given directory, and if in module there
> is instance of class then return instantiation of that class?

There are two libs that I'm aware of.

  http://hackage.haskell.org/cgi-bin/hackage-scripts/package/plugins-1.0
 
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/metaplug-0.1.
1

AFAICT, plugins is more mature and has a higher-level API, but the last
time I looked it was not working on Windows under ghc >= 6.6 (can anyone
refute or verify this?)

It's more like dynamic linking than Java's reflection: you have to
already know what functions are in the module (and their types) to be
able to call them. I'm not sure about directly creating values of data
types exported from the module.

Alistair
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