Re: [Haskell-cafe] Heist template splice functions and custom monad

Kevin Jardine writes:

I'd like to run Heist template splice functions in my own custom monad.

I can define a splice function as:

mySplice :: Splice MyMonad

However, when I try to call functions that return values in my monad in mySplice, I get a compile error:

Couldn't match expected type TemplateMonad MyMonad a against inferred type MyMonad ()

I've seen an example in the Heist documentation where the inner MyMonad is accessed using lift. But when I try that, I get another compile error:

No instance for (Monad Trans TemplateMonad) arising from the use of 'lift'

What do I do to get this to work?

You should post this to the Snap framework mailing list -- join here: http://mailman-mail5.webfaction.com/listinfo/snap. Please follow up there. TemplateMonad does have a MonadTrans instance: http://hackage.haskell.org/packages/archive/heist/0.2.0/doc/html/Text-Templa... Make sure you're using the "transformers"/"monads-fd" libraries and not "mtl". G -- Gregory Collins