diff options
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/iface/TcIface.lhs | 25 |
1 files changed, 11 insertions, 14 deletions
diff --git a/compiler/iface/TcIface.lhs b/compiler/iface/TcIface.lhs index 1efb11e21b..19b5cfe405 100644 --- a/compiler/iface/TcIface.lhs +++ b/compiler/iface/TcIface.lhs @@ -570,20 +570,17 @@ tcIfaceDataCons tycon_name tycon _ if_cons = bindIfaceTyVars univ_tvs $ \ univ_tyvars -> do bindIfaceTyVars ex_tvs $ \ ex_tyvars -> do { name <- lookupIfaceTop occ - ; eq_spec <- tcIfaceEqSpec spec - ; theta <- tcIfaceCtxt ctxt -- Laziness seems not worth the bother here - -- At one stage I thought that this context checking *had* - -- to be lazy, because of possible mutual recursion between the - -- type and the classe: - -- E.g. - -- class Real a where { toRat :: a -> Ratio Integer } - -- data (Real a) => Ratio a = ... - -- But now I think that the laziness in checking class ops breaks - -- the loop, so no laziness needed - - -- Read the argument types, but lazily to avoid faulting in - -- the component types unless they are really needed - ; arg_tys <- forkM (mk_doc name) (mapM tcIfaceType args) + + -- Read the context and argument types, but lazily for two reasons + -- (a) to avoid looking tugging on a recursive use of + -- the type itself, which is knot-tied + -- (b) to avoid faulting in the component types unless + -- they are really needed + ; ~(eq_spec, theta, arg_tys) <- forkM (mk_doc name) $ + do { eq_spec <- tcIfaceEqSpec spec + ; theta <- tcIfaceCtxt ctxt + ; arg_tys <- mapM tcIfaceType args + ; return (eq_spec, theta, arg_tys) } ; lbl_names <- mapM lookupIfaceTop field_lbls -- Remember, tycon is the representation tycon |