Hello All, I'm trying to write a splice to make HList type signatures a bit more concise, I don't know whether this is a good idea or not. I wrote a small function to do '[(Type,Type)] -> Q Type' for this, and got the following from GHC. Should I add this to the bug tracker? Details: THBug1.hs: {-# LANGUAGE TemplateHaskell #-} module THBug1 where import Data.HList import Language.Haskell.TH mhlt :: [(Type,Type)] -> Q Type mhlt x = [t| Record $(foldThing x)|] where foldThing ((f,t):xs) = [t|HCons (LVPair (Proxy $f) $t) $(foldThing xs)|] foldThing [] = [t|HNil|] ---- $ ghc -c THBug1.hs THBug1.hs:12:61: GHC internal error: `foldThing' is not in scope during type checking, but it passed the renamer tcg_type_env of environment: [] In the expression: foldThing xs In the Template Haskell quotation [t| HCons (LVPair (Proxy $f) $t) $(foldThing xs) |] In the expression: [t| HCons (LVPair (Proxy $f) $t) $(foldThing xs) |] I'm using GHC 6.12.1 from debian experimental: $ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.12.1 $ ghc-pkg list |grep template template-haskell-2.4.0.0 To get HList to install with GHC 6.12, I downloaded the latest version from http://old-darcs.well-typed.com/HList/ and altered it slightly, updated package here: http://launchpad.net/hssqlppp/prealpha/environment/+download/HList-0.2.tar.g... the changes I made are: diff -rN old-HList/Data/HList/GhcSyntax.hs new-HList/Data/HList/GhcSyntax.hs 2c2 < {-# LANGUAGE FlexibleContexts #-} ---

{-# LANGUAGE FlexibleContexts, TypeOperators #-} diff -rN old-HList/Data/HList/Label2.hs new-HList/Data/HList/Label2.hs 1c1,2 < {-# LANGUAGE FlexibleInstances, MultiParamTypeClasses, UndecidableInstances, EmptyDataDecls #-}

{-# LANGUAGE FlexibleInstances, MultiParamTypeClasses, UndecidableInstances, EmptyDataDecls, ExistentialQuantification #-} 36c37 < data HNat x => Label x ns desc -- labels are exclusively type-level entities

data Label x ns desc = HNat x => Label x ns desc -- labels are exclusively type-level entities diff -rN old-HList/Data/HList/Label3.hs new-HList/Data/HList/Label3.hs 1c1,2 < {-# LANGUAGE FlexibleInstances, MultiParamTypeClasses, UndecidableInstances, EmptyDataDecls #-}

{-# LANGUAGE FlexibleInstances, MultiParamTypeClasses, UndecidableInstances, EmptyDataDecls, ExistentialQuantification #-} 37c38 < data HNat x => Label x ns desc -- labels are exclusively type-level entities

data Label x ns desc = HNat x => Label x ns desc -- labels are exclusively type-level entities

(If it's not obvious, I have no idea what I'm doing..., but my small amount of code which uses HList worked fine with this altered package.) Thanks, Jake Wheat