diff options
Diffstat (limited to 'compiler/deSugar/DsUtils.lhs')
| -rw-r--r-- | compiler/deSugar/DsUtils.lhs | 15 |
1 files changed, 12 insertions, 3 deletions
diff --git a/compiler/deSugar/DsUtils.lhs b/compiler/deSugar/DsUtils.lhs index cf171ce537..2254ec2319 100644 --- a/compiler/deSugar/DsUtils.lhs +++ b/compiler/deSugar/DsUtils.lhs @@ -168,8 +168,8 @@ mk_val_app (Var f `App` Type ty1 `App` Type _ `App` arg1) arg2 _ res_ty = Case arg1 case_bndr res_ty [(DEFAULT,[],arg2)] where case_bndr = case arg1 of - Var v1 -> v1 -- Note [Desugaring seq (2)] - _ -> mkWildId ty1 + Var v1 | isLocalId v1 -> v1 -- Note [Desugaring seq (2) and (3)] + _ -> mkWildId ty1 mk_val_app fun arg arg_ty _ -- See Note [CoreSyn let/app invariant] | not (isUnLiftedType arg_ty) || exprOkForSpeculation arg @@ -220,7 +220,7 @@ the seq, by re-introducing the space leak: We can try to avoid doing this by ensuring that the binder-swap in the case happens, so we get his at an early stage: case chp of chp2 { I# -> ...chp2... } -But this is fragile. The real culprit is the source program. Perhpas we +But this is fragile. The real culprit is the source program. Perhaps we should have said explicitly let !chp2 = chp in ...chp2... @@ -234,6 +234,15 @@ Notice the shadowing of the case binder! And now all is well. The reason it's a hack is because if you define mySeq=seq, the hack won't work on mySeq. +Note [Desugaring seq (3)] cf Trac #2409 +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The isLocalId ensures that we don't turn + True `seq` e +into + case True of True { ... } +which stupidly tries to bind the datacon 'True'. + + %************************************************************************ %* * \subsection{ Selecting match variables} |