[Haskell-cafe] Is there a way to generate instances from the GHCi REPL?

Michael Sloan mgsloan at gmail.com
Fri Feb 5 01:29:05 UTC 2016

One thing to note is that the qAddTopDecls issue isn't a fundamental issue,
just a matter of implementation:

On Thu, Feb 4, 2016 at 6:56 AM, Christopher Done <chrisdone at gmail.com>

> Good evening,
> Is there a way with TH to generate instances for a class in GHCi? I want
> to generate instances for a serialization class.
> I tried to write some TH to do it, but $(foo) in GHCi’s REPL says that it
> can only be Q Exp, not Q [Dec]. Sadness.
> I found qAddTopDecls. I tried to add the class declarations via $(foo >>=
> qAddTopDecls; stringE "OK!") and it says “Only function, value, and
> foreign import declarations may be added with addTopDecl". Woe.
> I could create a file and then load in that file, but loading modules
> loses all GHCi's state, which would defeat the purpose of using a REPL in
> the first place.
> Any hope?
> Ciao!
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