[Haskell-cafe] Template Haskell antiquotation in user-defined quasiquoters

[Sam Lindley]

Template Haskell supports antiquotation for built-in quasiquotes, e.g.:

   [| \x -> x + $([|3 * 4|]) |]

However, as far as I can tell, there is no way of supporting 
antiquotation in user-defined quasiquoters, because the only way to 
specify a new quasiquoter is through a quoteExp function of type String 
-> Q Exp. Of course, it is perfectly possible to write a parser for some 
fragment of Haskell inside your quoteExp function, but that seems crazy 
given that Template Haskell or rather GHC already implements a parser 
for the whole language.

I know about Language.Haskell.Exts.Parser in haskell-src-exts, which 
provides parseExp :: String -> ParseResult Exp, but that Exp is a 
different type to the one provided by Template 
Haskell.<http://hackage.haskell.org/packages/archive/haskell-src-exts/1.9.0/doc/html/Language-Haskell-Exts-Syntax.html#t:Exp> 
I'm also aware of Dominic Orchard's syntax-trees package, which supports 
converting between the two representations using a cunning hack that 
pretty-prints the haskell-src-exts representation to a string and uses 
Template Haskell to parse it back.

Is there a saner way of simulating antiquotation in user-defined 
quasiquoters?

Sam


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