[Template-haskell] How to get list of instances of a given class?

Simon Peyton-Jones simonpj at microsoft.com
Fri Dec 16 09:44:16 EST 2005

There's currently no way to get the list of instances of a class.  It
would not be very difficult to add this.   Any volunteers?  Or I could
do it if there is serious demand.  How much difference would it make?

I've added a note to the Hawiki page about TH, and pointed to it from
GHC's wiki.

A really desirable thing would be for someone to write Haddock
documentation for the Template Haskell API.  Would someone be willing to
do that?


| -----Original Message-----
| From: template-haskell-bounces at haskell.org
[mailto:template-haskell-bounces at haskell.org] On
| Behalf Of Dimitry Golubovsky
| Sent: 13 December 2005 14:38
| To: template-haskell at haskell.org
| Subject: [Template-haskell] How to get list of instances of a given
| Bulat kindly pointed me to the SerTH example. I also have been trying
| to browse the GHC documentation trying to find the answer to my
| quesitons.
| I see, for example, what can be gotten for a class (provided that the
| name of the class is known):
| data Dec
| ...
| ClassD Cxt String [String] [Dec]  -- or ClassD Cxt Name [Name]
| [FunDep] [Dec] in
|                                                 --6.4.x
| InstanceD Cxt Type [Dec]
| ...
| The documentation (neither for 6.2.2 nor for the latest) says nothing
| about what is in [Dec] for a class. Are instances of the class known
| at the moment of slplicing contained there?
| I may be asking too common questions. I just need to see whether my
| task is accomplishable via TH. If it is not, then I'll do this via
| some plugins to HSFFIG, but the latter is not much desirable.
| Please advise.
| Thanks.
| --
| Dimitry Golubovsky
| Anywhere on the Web

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