id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
6089	Allow declaration splices inside declaration brackets	igloo	simonpj	"I would like to be able to write code like:
{{{
{-# LANGUAGE TemplateHaskell #-}

import Language.Haskell.TH

decs :: Q [Dec]
decs = [d| data MyType = MyCon | MyOtherCon

           val1 :: MyType
           val1 = MyCon

           val2 :: MyType
           val2 = MyOtherCon

           $( do let mkFun v i = [| if $v == i then val1 else val2 |]
                 [d| fun3 x = $(mkFun [| x |] 3)
                     fun4 x = $(mkFun [| x |] 4) |] ) |]
}}}
but GHC says:
{{{
$ ghci decSplices.hs
GHCi, version 7.5.20120420: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
[1 of 1] Compiling Main             ( decSplices.hs, interpreted )

decSplices.hs:15:15:
    Declaration splices are not permitted inside declaration brackets
Failed, modules loaded: none.
}}}

As far as I can see there is no technical reason why this couldn't work, with a splice within a declaration bracket splitting the declarations into 3. The declarations before the splice would be renamed, typechecked etc first, then those in the splice, and finally those after the splice.
"	feature request	new	normal	7.8.1	Template Haskell	7.4.1				Unknown/Multiple	Unknown/Multiple	GHC rejects valid program	Unknown