On 3 February 2010 14:07, Sebastian Fischer
With a class-based approach only one parser that creates values of the same type could be used in a program. It would not be possible to embed multiple languages that create TH.Exp to be spliced into a single program. With the current syntax, I can write [$myLang| ... |] and [$yourLang| ... |] in the same program and use different parsers although both create Exp values.
This is not the case, because you still have an instance "Quoted String". Then you can write: $(myLang [|..|]) Where myLang :: String -> Q Exp The "Quoted Exp" instance you have in scope just determines what default semantics for $([|...|]) you get! So you can use this behaviour to change the default "language" from Haskell to whatever you like, but importing a My.Lang.Module rather than Language.Haskell.TH. This is a bit ugly though, and is more of an unintentional feature than something I was designing for :-)
This is more verbose than the proposed [myLang| ... |]. There seem to be different goals in the different proposals in this thread: 1. Simplify the syntax for quasi quoting (remove $, use different brackets), 2. make it more generally applicable (allow declarations and/or types to be quasi quoted), and 3. simplify and generalise its implementation (invent a single mechanism that unifies quasi quoting and TH splicing).
Yes - I should have made it clearer that our proposal had strayed rather far from the original goal of reducing verbosity :-). Instead it increases it in the QQ case - but in (IMHO) a good way. Cheers, Max