GitLab

Marc Weber writes: this doesn't work:

-- packages: template-haskell
{-# OPTIONS_GHC -XTemplateHaskell #-}
module Main where
import Language.Haskell.TH

data A a = A a

type C = A Int

data ABC = ABC Int

$(do
  a <- reify $ mkName "C"
  report False $ show a
  return []
  )
main = print ""

Produces output

|| [1 of 1] Compiling Main             ( test.hs, test.o )
||
test.hs|1| `C' is not in scope at a reify

Using mkName "A" results in

test.hs|1 error|
||     DataConI Main.A (ForallT [a_1627391370] [] (AppT (AppT ArrowT (VarT a_1627391370)) (AppT (ConT Main.A) (VarT a_1627391370)))) Main.A (Fixity 9 InfixL)

as expected

Why do I need it? I'd like to implement kind of very basic relational data representation the way IxSet is doing it but without dynamics..

It will look like this:

type CDs = Table (Autoinc, Artist, Title, Year) -- col types
                 (Artist, Title, Year) -- keys
                 () -- is detail of
type Tracks = Table (Autoinc, Title, RecordingDate)
                    (Title, RecordingDate)
                    (CDs)
$(mkDB ["CDs","Tracks"])

To be able to automatically derive

insert{CDs,Tracks}
delete{CDs,Tracks}
update{CDs,Tracks}

functions I need to get information about those types.. Is this possible?

Thanks Marc Weber

Trac metadata

Trac field	Value
Version	6.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Template Haskell
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown