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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2012-05-02 15:44:14 +0100 |
|---|---|---|
| committer | Simon Peyton Jones <simonpj@microsoft.com> | 2012-05-02 15:44:14 +0100 |
| commit | ac230c5ef652e27f61d954281ae6a3195e1f9970 (patch) | |
| tree | 4cd59d3ca670916f64bcfe9c0c3f72f21a272e42 /compiler/iface/IfaceSyn.lhs | |
| parent | b04c0beb951b2e69f76f724a4e72b98c896b468a (diff) | |
| download | haskell-ac230c5ef652e27f61d954281ae6a3195e1f9970.tar.gz | |
Allow cases with empty alterantives
This patch allows, for the first time, case expressions with an empty
list of alternatives. Max suggested the idea, and Trac #6067 showed
that it is really quite important.
So I've implemented the idea, fixing #6067. Main changes
* See Note [Empty case alternatives] in CoreSyn
* Various foldr1's become foldrs
* IfaceCase does not record the type of the alternatives.
I added IfaceECase for empty-alternative cases.
* Core Lint does not complain about empty cases
* MkCore.castBottomExpr constructs an empty-alternative case
expression (case e of ty {})
* CoreToStg converts '(case e of {})' to just 'e'
Diffstat (limited to 'compiler/iface/IfaceSyn.lhs')
| -rw-r--r-- | compiler/iface/IfaceSyn.lhs | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/compiler/iface/IfaceSyn.lhs b/compiler/iface/IfaceSyn.lhs index d3e44fe54f..b53398da7d 100644 --- a/compiler/iface/IfaceSyn.lhs +++ b/compiler/iface/IfaceSyn.lhs @@ -249,6 +249,7 @@ data IfaceExpr | IfaceLam IfaceBndr IfaceExpr | IfaceApp IfaceExpr IfaceExpr | IfaceCase IfaceExpr IfLclName [IfaceAlt] + | IfaceECase IfaceExpr IfaceType -- See Note [Empty case alternatives] | IfaceLet IfaceBinding IfaceExpr | IfaceCast IfaceExpr IfaceCoercion | IfaceLit Literal @@ -279,6 +280,12 @@ data IfaceBinding data IfaceLetBndr = IfLetBndr IfLclName IfaceType IfaceIdInfo \end{code} +Note [Empty case alternatives] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +In IfaceSyn an IfaceCase does not record the types of the alternatives, +unlike CorSyn Case. But we need this type if the alternatives are empty. +Hence IfaceECase. See Note [Empty case alternatives] in CoreSyn. + Note [Expose recursive functions] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ For supercompilation we want to put *all* unfoldings in the interface @@ -621,6 +628,11 @@ pprIfaceExpr add_par i@(IfaceLam _ _) collect bs (IfaceLam b e) = collect (b:bs) e collect bs e = (reverse bs, e) +pprIfaceExpr add_par (IfaceECase scrut ty) + = add_par (sep [ ptext (sLit "case") <+> pprIfaceExpr noParens scrut + , ptext (sLit "ret_ty") <+> pprParendIfaceType ty + , ptext (sLit "of {}") ]) + pprIfaceExpr add_par (IfaceCase scrut bndr [(con, bs, rhs)]) = add_par (sep [ptext (sLit "case") <+> pprIfaceExpr noParens scrut <+> ptext (sLit "of") @@ -856,7 +868,7 @@ freeNamesIfExpr (IfaceLam b body) = freeNamesIfBndr b &&& freeNamesIfExpr body freeNamesIfExpr (IfaceApp f a) = freeNamesIfExpr f &&& freeNamesIfExpr a freeNamesIfExpr (IfaceCast e co) = freeNamesIfExpr e &&& freeNamesIfType co freeNamesIfExpr (IfaceTick _ e) = freeNamesIfExpr e - +freeNamesIfExpr (IfaceECase e ty) = freeNamesIfExpr e &&& freeNamesIfType ty freeNamesIfExpr (IfaceCase s _ alts) = freeNamesIfExpr s &&& fnList fn_alt alts &&& fn_cons alts |