I'd like to use quasiquotation to emulate bash's case statement in Haskell. That is, I'd like to turn

example x = case x of [$rx|.*foo.*] -> "contains foo" _ -> "doesn't contain foo"

Assuming that regexqq produces (String -> Maybe [String]), and works rather better for expressions than for patterns, you could simply lift mplus to functions, and define your own caseRE (your example doesn't really make use of case/pattern-matching): import Control.Monad import Data.Char import Data.List (matchA .|. matchB) x = matchA x `mplus` matchB x (regex .->. rhs) x = regex x >> return rhs -- (or >>=, if prefered) caseRE x matches otherwise = maybe otherwise id (matches x) a x = Just [this,that] where (this,that) = span isSpace x b x = Nothing test = caseRE "hello world" ( (b .->. "hi") .|. (a .->. "ho")) "otherwise" Then you can either fiddle with operator priorities, or drop the thin facade and use MonadPlus directly;-) You might also want to be able to refer to match results in the rhs, no matter whether that is possible in bash - this would seem to need control over both lhs and rhs anyway. Hth, Claus

into (assuming an appropriate match :: String -> String -> Bool)

example x = case x of s | match ".*foo.*" s -> "contains foo" _ -> "doesn't contain foo"

But it seems like I can't do so, because despite appearances, the difference between the two cases in the second example is not in "what's to the left of ->". Instead, the first has a GuardedB body while the second has a NormalB body. (Having reread the Haskell Report, I now understand why this is, but it was surprising at first.) Whatever my definition of the quasiquoter rx is, the first example is going to expand to something with two NormalB bodies, so I can't achieve the desired expansion.

Is there a clever workaround? I tried (ab)using view patterns, but they're not yet supported by Template Haskell.

Regards, Reid Barton _______________________________________________ template-haskell mailing list template-haskell@haskell.org http://www.haskell.org/mailman/listinfo/template-haskell