Уточнение типа по мере продвижения по файлу

H.hs

{-# LANGUAGE TemplateHaskell #-}
module H where

import Language.Haskell.TH

f = [42]

$(do
    i <- reify (mkName "f")
    runIO (print i)
    sequence [dataD (cxt []) (mkName "A") [] [normalC (mkName "A") []] []])

main = do
  case f :: [Integer] of
    [42] -> print "A"
    _ -> print "B"

$(do
    i <- reify (mkName "f")
    runIO (print i)
    sequence [dataD (cxt []) (mkName "B") [] [normalC (mkName "B") []] []])

H.log

VarI H.f (AppT ListT (VarT t_1946157057)) Nothing (Fixity 9 InfixL)
VarI H.f (AppT ListT (ConT GHC.Integer.Type.Integer)) Nothing (Fixity 9 InfixL)