diff options
| -rw-r--r-- | compiler/typecheck/TcRnDriver.lhs | 24 |
1 files changed, 19 insertions, 5 deletions
diff --git a/compiler/typecheck/TcRnDriver.lhs b/compiler/typecheck/TcRnDriver.lhs index 8f11232737..d1333b3833 100644 --- a/compiler/typecheck/TcRnDriver.lhs +++ b/compiler/typecheck/TcRnDriver.lhs @@ -887,16 +887,30 @@ tcRnStmt hsc_env ictxt rdr_stmt bound_names = map idName global_ids ; new_rn_env = extendLocalRdrEnv rn_env bound_names ; - -- Remove any shadowed bindings from the type_env; - -- they are inaccessible but might, I suppose, cause - -- a space leak if we leave them there +{- --------------------------------------------- + At one stage I removed any shadowed bindings from the type_env; + they are inaccessible but might, I suppose, cause a space leak if we leave them there. + However, with Template Haskell they aren't necessarily inaccessible. Consider this + GHCi session + Prelude> let f n = n * 2 :: Int + Prelude> fName <- runQ [| f |] + Prelude> $(return $ AppE fName (LitE (IntegerL 7))) + 14 + Prelude> let f n = n * 3 :: Int + Prelude> $(return $ AppE fName (LitE (IntegerL 7))) + In the last line we use 'fName', which resolves to the *first* 'f' + in scope. If we delete it from the type env, GHCi crashes because + it doesn't expect that. + + Hence this code is commented out + shadowed = [ n | name <- bound_names, let rdr_name = mkRdrUnqual (nameOccName name), Just n <- [lookupLocalRdrEnv rn_env rdr_name] ] ; - filtered_type_env = delListFromNameEnv type_env shadowed ; - new_type_env = extendTypeEnvWithIds filtered_type_env global_ids ; +-------------------------------------------------- -} + new_type_env = extendTypeEnvWithIds type_env global_ids ; new_ic = ictxt { ic_rn_local_env = new_rn_env, ic_type_env = new_type_env } } ; |