Re: [Haskell-cafe] Template Haskell - substitution in pattern in a lambda
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 For the Pat, you would use eiter VarP or WildP for variable binding patterns or wild-card patterns. Or am I missing something? Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Template Haskell - substitution in pattern in a lambda
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. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Template Haskell - substitution in pattern in a lambda
2010/1/4 Patrick Caldon p...@pessce.net 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? Below is what I've been playing with to try to make this work. Thanks, Patrick. Here's something pretty generic that gets the patterns right: module THTest where import Language.Haskell.TH import Data.List import Control.Monad type Policy = Int data Management = SimpleM Policy Policy Policy deriving Show buildCP :: Name - Int - Int - ExpQ buildCP ctor nVars nth = do names - replicateM nVars $ newName pat let p1 = replaceAt nth WildP $ map VarP names p2 = replaceAt nth (VarP $ names!!nth) $ replicate nVars WildP return $ LamE [ConP ctor p1, ConP ctor p2] (ListE $ map VarE names) replaceAt :: Int - a - [a] - [a] replaceAt pos x xs = let (first,_:rest) = splitAt pos xs in first ++ [x] ++ rest -- for example: doFst = $(buildCP 'SimpleM 3 0) doFst (SimpleM 1 2 3) (SimpleM 4 5 6) == [4,2,3] (returns a list because it's easier to do. Modifying it to return SimpleM left as an exercise :) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Template Haskell - substitution in pattern in a lambda
Tuomas Tynkkynen wrote: Here's something pretty generic that gets the patterns right: Thanks for that - about 2/3rds of the length of my proposed solution! Cheers, Patrick. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
