Antoine Latter wrote:
On Sun, Jan 3, 2010 at 8:30 PM, Patrick Caldon <p...@pessce.net> wrote:
I'm trying to write some template haskell which will transform:
$(buildCP 0) into \(SimpleM d1 d2 d3) (SimpleM _ _ _) -> (SimpleM d1 d2 d3)
$(buildCP 1) into \(SimpleM _ d2 d3) (SimpleM d1 _ _) -> (SimpleM d1 d2 d3)
$(buildCP 1) into \(SimpleM d1 _ d3) (SimpleM _ d2 _) -> (SimpleM d1 d2 d3)
and so on.
Ultimately I want to generalize this to more variables.
I can't seem to get anything to substitute for the pattern variables in a
lambda. Is there a straightforward way of doing this?
Hello,
It looks like you want to construct expressions with the LamE
constructor, which is declared like so:
LamE [Pat] Exp
Thanks - I see how that could work, I'll try it.
But really I was wondering if there was something like:
buildCP2 :: Int -> ExpQ
buildCP2 k =
[|\(SimpleM ~a1 ~a2 ~a3) (SimpleM ~b1 ~b2 ~b3) -> (SimpleM $e1 $e2
$e3) |]
where (e1,a1,b1) = bitToExprs 0 k
(e2,a2,b2) = bitToExprs 1 k
(e3,a3,b3) = bitToExprs 2 k
bitToExprs:: Int -> Int -> (ExpQ,PatQ,PatQ)
Where ~a1 would mean "look for something called a1 returning a pattern,
and slot it into the pattern part of the lambda in the appropriate spot".
I'm guessing no such syntax exists?
Thanks again,
Patrick.
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