diff options
| -rw-r--r-- | compiler/deSugar/DsExpr.lhs | 19 |
1 files changed, 18 insertions, 1 deletions
diff --git a/compiler/deSugar/DsExpr.lhs b/compiler/deSugar/DsExpr.lhs index 6844f48970..10d20d37da 100644 --- a/compiler/deSugar/DsExpr.lhs +++ b/compiler/deSugar/DsExpr.lhs @@ -191,7 +191,11 @@ dsLExpr (L loc e) = putSrcSpanDs loc $ dsExpr e dsExpr :: HsExpr Id -> DsM CoreExpr dsExpr (HsPar e) = dsLExpr e dsExpr (ExprWithTySigOut e _) = dsLExpr e -dsExpr (HsVar var) = return (varToCoreExpr var) -- See Note [Desugaring vars] +dsExpr (HsVar var) -- See Note [Unfolding while desugaring] + | isCompulsoryUnfolding unfolding = return $ unfoldingTemplate unfolding + | otherwise = return (varToCoreExpr var) -- See Note [Desugaring vars] + where + unfolding = idUnfolding var dsExpr (HsIPVar _) = panic "dsExpr: HsIPVar" dsExpr (HsLit lit) = dsLit lit dsExpr (HsOverLit lit) = dsOverLit lit @@ -220,6 +224,19 @@ dsExpr (HsApp fun arg) dsExpr (HsUnboundVar _) = panic "dsExpr: HsUnboundVar" \end{code} +Note [Unfolding while desugaring] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Variables with compulsory unfolding must be substituted at desugaring +time. This is needed to preserve the let/app invariant in cases where +the unfolding changes whether wrapping in a case is needed. +Suppose we have a call like this: + I# x +where 'x' has an unfolding like this: + f void# +In this case, 'mkCoreAppDs' needs to see 'f void#', not 'x', to be +able to do the right thing. + + Note [Desugaring vars] ~~~~~~~~~~~~~~~~~~~~~~ In one situation we can get a *coercion* variable in a HsVar, namely |