| 'return' maybe_actuals ';'
{ do e <- sequence $2; stmtEC (CmmReturn e) }
| 'if' bool_expr '{' body '}' else
- { ifThenElse $2 $4 $6 }
+ { cmmIfThenElse $2 $4 $6 }
opt_never_returns :: { CmmReturnInfo }
: { CmmMayReturn }
-- ToDo: smart constructors which simplify the boolean expression.
-ifThenElse cond then_part else_part = do
+cmmIfThenElse cond then_part else_part = do
then_id <- code newLabelC
join_id <- code newLabelC
c <- cond
liftM2 HsCase
(addTickLHsExpr e)
(addTickMatchGroup mgs)
-addTickHsExpr (HsIf e1 e2 e3) =
- liftM3 HsIf
+addTickHsExpr (HsIf cnd e1 e2 e3) =
+ liftM3 (HsIf cnd)
(addBinTickLHsExpr (BinBox CondBinBox) e1)
(addTickLHsExprOptAlt True e2)
(addTickLHsExprOptAlt True e3)
-- if e then Left ((xs1)*ts) else Right ((xs2)*ts)) >>>
-- c1 ||| c2
-dsCmd ids local_vars env_ids stack res_ty (HsIf cond then_cmd else_cmd) = do
+dsCmd ids local_vars env_ids stack res_ty (HsIf mb_fun cond then_cmd else_cmd) = do
core_cond <- dsLExpr cond
(core_then, fvs_then, then_ids) <- dsfixCmd ids local_vars stack res_ty then_cmd
(core_else, fvs_else, else_ids) <- dsfixCmd ids local_vars stack res_ty else_cmd
either_con <- dsLookupTyCon eitherTyConName
left_con <- dsLookupDataCon leftDataConName
right_con <- dsLookupDataCon rightDataConName
- let
- left_expr ty1 ty2 e = mkConApp left_con [Type ty1, Type ty2, e]
- right_expr ty1 ty2 e = mkConApp right_con [Type ty1, Type ty2, e]
+
+ let mk_left_expr ty1 ty2 e = mkConApp left_con [Type ty1, Type ty2, e]
+ mk_right_expr ty1 ty2 e = mkConApp right_con [Type ty1, Type ty2, e]
in_ty = envStackType env_ids stack
then_ty = envStackType then_ids stack
else_ty = envStackType else_ids stack
sum_ty = mkTyConApp either_con [then_ty, else_ty]
fvs_cond = exprFreeVars core_cond `intersectVarSet` local_vars
-
- core_if <- matchEnvStack env_ids stack_ids
- (mkIfThenElse core_cond
- (left_expr then_ty else_ty (buildEnvStack then_ids stack_ids))
- (right_expr then_ty else_ty (buildEnvStack else_ids stack_ids)))
+
+ core_left = mk_left_expr then_ty else_ty (buildEnvStack then_ids stack_ids)
+ core_right = mk_right_expr then_ty else_ty (buildEnvStack else_ids stack_ids)
+
+ core_if <- case mb_fun of
+ Just fun -> do { core_fun <- dsExpr fun
+ ; matchEnvStack env_ids stack_ids $
+ mkCoreApps core_fun [core_cond, core_left, core_right] }
+ Nothing -> matchEnvStack env_ids stack_ids $
+ mkIfThenElse core_cond core_left core_right
+
return (do_map_arrow ids in_ty sum_ty res_ty
core_if
(do_choice ids then_ty else_ty res_ty core_then core_else),
where
[elt_ty] = tcTyConAppArgs result_ty
-dsExpr (HsIf guard_expr then_expr else_expr)
- = mkIfThenElse <$> dsLExpr guard_expr <*> dsLExpr then_expr <*> dsLExpr else_expr
+dsExpr (HsIf mb_fun guard_expr then_expr else_expr)
+ = do { pred <- dsLExpr guard_expr
+ ; b1 <- dsLExpr then_expr
+ ; b2 <- dsLExpr else_expr
+ ; case mb_fun of
+ Just fun -> do { core_fun <- dsExpr fun
+ ; return (mkCoreApps core_fun [pred,b1,b2]) }
+ Nothing -> return $ mkIfThenElse pred b1 b2 }
\end{code}
repE (HsCase e (MatchGroup ms _)) = do { arg <- repLE e
; ms2 <- mapM repMatchTup ms
; repCaseE arg (nonEmptyCoreList ms2) }
-repE (HsIf x y z) = do
+repE (HsIf _ x y z) = do
a <- repLE x
b <- repLE y
c <- repLE z
repTup (MkC es) = rep2 tupEName [es]
repCond :: Core TH.ExpQ -> Core TH.ExpQ -> Core TH.ExpQ -> DsM (Core TH.ExpQ)
-repCond (MkC x) (MkC y) (MkC z) = rep2 condEName [x,y,z]
+repCond (MkC x) (MkC y) (MkC z) = rep2 condEName [x,y,z]
repLetE :: Core [TH.DecQ] -> Core TH.ExpQ -> DsM (Core TH.ExpQ)
repLetE (MkC ds) (MkC e) = rep2 letEName [ds, e]
lexp e1 e1' && lexp e2 e2'
exp (ExplicitTuple es1 _) (ExplicitTuple es2 _) =
eq_list tup_arg es1 es2
- exp (HsIf e e1 e2) (HsIf e' e1' e2') =
+ exp (HsIf _ e e1 e2) (HsIf _ e' e1' e2') =
lexp e e' && lexp e1 e1' && lexp e2 e2'
-- Enhancement: could implement equality for more expressions
; return $ HsLam (mkMatchGroup [mkSimpleMatch ps' e']) }
cvt (TupE [e]) = cvt e -- Singleton tuples treated like nothing (just parens)
cvt (TupE es) = do { es' <- mapM cvtl es; return $ ExplicitTuple (map Present es') Boxed }
- cvt (CondE x y z) = do { x' <- cvtl x; y' <- cvtl y; z' <- cvtl z
- ; return $ HsIf x' y' z' }
+ cvt (CondE x y z) = do { x' <- cvtl x; y' <- cvtl y; z' <- cvtl z;
+ ; return $ HsIf (Just noSyntaxExpr) x' y' z' }
cvt (LetE ds e) = do { ds' <- cvtLocalDecs (ptext (sLit "a let expression")) ds
; e' <- cvtl e; return $ HsLet ds' e' }
cvt (CaseE e ms)
| HsCase (LHsExpr id)
(MatchGroup id)
- | HsIf (LHsExpr id) -- predicate
+ | HsIf (Maybe (SyntaxExpr id)) -- cond function
+ -- Nothing => use the built-in 'if'
+ -- See Note [Rebindable if]
+ (LHsExpr id) -- predicate
(LHsExpr id) -- then part
(LHsExpr id) -- else part
-- pasted back in by the desugarer
\end{code}
-A @Dictionary@, unless of length 0 or 1, becomes a tuple. A
-@ClassDictLam dictvars methods expr@ is, therefore:
-\begin{verbatim}
-\ x -> case x of ( dictvars-and-methods-tuple ) -> expr
-\end{verbatim}
+Note [Rebindable if]
+~~~~~~~~~~~~~~~~~~~~
+The rebindable syntax for 'if' is a bit special, because when
+rebindable syntax is *off* we do not want to treat
+ (if c then t else e)
+as if it was an application (ifThenElse c t e). Why not?
+Because we allow an 'if' to return *unboxed* results, thus
+ if blah then 3# else 4#
+whereas that would not be possible using a all to a polymorphic function
+(because you can't call a polymorphic function at an unboxed type).
+
+So we use Nothing to mean "use the old built-in typing rule".
\begin{code}
instance OutputableBndr id => Outputable (HsExpr id) where
nest 2 (pprMatches (CaseAlt `asTypeOf` idType exprType) matches <+> char '}') ]
where idType :: HsExpr id -> HsMatchContext id; idType = undefined
-ppr_expr (HsIf e1 e2 e3)
+ppr_expr (HsIf _ e1 e2 e3)
= sep [hsep [ptext (sLit "if"), nest 2 (ppr e1), ptext (sLit "then")],
nest 4 (ppr e2),
ptext (sLit "else"),
[Match id] -- bodies are HsCmd's
SrcLoc
- | HsIf (HsExpr id) -- predicate
+ | HsIf (Maybe (SyntaxExpr id)) -- cond function
+ (HsExpr id) -- predicate
(HsCmd id) -- then part
(HsCmd id) -- else part
SrcLoc
-- Terms
mkHsPar, mkHsApp, mkHsConApp, mkSimpleHsAlt,
mkSimpleMatch, unguardedGRHSs, unguardedRHS,
- mkMatchGroup, mkMatch, mkHsLam,
+ mkMatchGroup, mkMatch, mkHsLam, mkHsIf,
mkHsWrap, mkLHsWrap, mkHsWrapCoI, mkLHsWrapCoI,
coiToHsWrapper, mkHsDictLet,
mkHsOpApp, mkHsDo, mkHsWrapPat, mkHsWrapPatCoI,
mkHsDo ctxt stmts body = HsDo ctxt stmts body placeHolderType
+mkHsIf :: LHsExpr id -> LHsExpr id -> LHsExpr id -> HsExpr id
+mkHsIf c a b = HsIf (Just noSyntaxExpr) c a b
+
mkNPat lit neg = NPat lit neg noSyntaxExpr
mkNPlusKPat id lit = NPlusKPat id lit noSyntaxExpr noSyntaxExpr
nlHsLam match = noLoc (HsLam (mkMatchGroup [match]))
nlHsPar e = noLoc (HsPar e)
-nlHsIf cond true false = noLoc (HsIf cond true false)
+nlHsIf cond true false = noLoc (mkHsIf cond true false)
nlHsCase expr matches = noLoc (HsCase expr (mkMatchGroup matches))
nlList exprs = noLoc (ExplicitList placeHolderType exprs)
| Opt_GADTs
| Opt_NPlusKPatterns
| Opt_DoAndIfThenElse
+ | Opt_RebindableSyntax
| Opt_StandaloneDeriving
| Opt_DeriveDataTypeable
( "MonomorphismRestriction", Opt_MonomorphismRestriction, nop ),
( "NPlusKPatterns", Opt_NPlusKPatterns, nop ),
( "DoAndIfThenElse", Opt_DoAndIfThenElse, nop ),
+ ( "RebindableSyntax", Opt_RebindableSyntax, nop ),
( "MonoPatBinds", Opt_MonoPatBinds, nop ),
( "ExplicitForAll", Opt_ExplicitForAll, nop ),
( "AlternativeLayoutRule", Opt_AlternativeLayoutRule, nop ),
, (Opt_ExistentialQuantification, Opt_ExplicitForAll)
, (Opt_PolymorphicComponents, Opt_ExplicitForAll)
+ , (Opt_RebindableSyntax, Opt_ImplicitPrelude)
+
, (Opt_GADTs, Opt_MonoLocalBinds)
, (Opt_TypeFamilies, Opt_MonoLocalBinds)
| 'let' binds 'in' exp { LL $ HsLet (unLoc $2) $4 }
| 'if' exp optSemi 'then' exp optSemi 'else' exp
{% checkDoAndIfThenElse $2 $3 $5 $6 $8 >>
- return (LL $ HsIf $2 $5 $8) }
+ return (LL $ mkHsIf $2 $5 $8) }
| 'case' exp 'of' altslist { LL $ HsCase $2 (mkMatchGroup (unLoc $4)) }
| '-' fexp { LL $ NegApp $2 noSyntaxExpr }
%* *
Rebindable names
Dealing with rebindable syntax is driven by the
- Opt_NoImplicitPrelude dynamic flag.
+ Opt_RebindableSyntax dynamic flag.
In "deriving" code we don't want to use rebindable syntax
so we switch off the flag locally
lookupSyntaxName :: Name -- The standard name
-> RnM (SyntaxExpr Name, FreeVars) -- Possibly a non-standard name
lookupSyntaxName std_name
- = xoptM Opt_ImplicitPrelude `thenM` \ implicit_prelude ->
- if implicit_prelude then normal_case
+ = xoptM Opt_RebindableSyntax `thenM` \ rebindable_on ->
+ if not rebindable_on then normal_case
else
-- Get the similarly named thing from the local environment
lookupOccRn (mkRdrUnqual (nameOccName std_name)) `thenM` \ usr_name ->
lookupSyntaxTable :: [Name] -- Standard names
-> RnM (SyntaxTable Name, FreeVars) -- See comments with HsExpr.ReboundNames
lookupSyntaxTable std_names
- = xoptM Opt_ImplicitPrelude `thenM` \ implicit_prelude ->
- if implicit_prelude then normal_case
+ = xoptM Opt_RebindableSyntax `thenM` \ rebindable_on ->
+ if not rebindable_on then normal_case
else
-- Get the similarly named thing from the local environment
mapM (lookupOccRn . mkRdrUnqual . nameOccName) std_names `thenM` \ usr_names ->
where
doc = text "In an expression type signature"
-rnExpr (HsIf p b1 b2)
- = rnLExpr p `thenM` \ (p', fvP) ->
- rnLExpr b1 `thenM` \ (b1', fvB1) ->
- rnLExpr b2 `thenM` \ (b2', fvB2) ->
- return (HsIf p' b1' b2', plusFVs [fvP, fvB1, fvB2])
+rnExpr (HsIf _ p b1 b2)
+ = do { (p', fvP) <- rnLExpr p
+ ; (b1', fvB1) <- rnLExpr b1
+ ; (b2', fvB2) <- rnLExpr b2
+ ; rebind <- xoptM Opt_RebindableSyntax
+ ; if not rebind
+ then return (HsIf Nothing p' b1' b2', plusFVs [fvP, fvB1, fvB2])
+ else do { c <- liftM HsVar (lookupOccRn (mkVarUnqual (fsLit "ifThenElse")))
+ ; return (HsIf (Just c) p' b1' b2', plusFVs [fvP, fvB1, fvB2]) }}
rnExpr (HsType a)
= rnHsTypeFVs doc a `thenM` \ (t, fvT) ->
convertOpFormsCmd (HsCase exp matches)
= HsCase exp (convertOpFormsMatch matches)
-convertOpFormsCmd (HsIf exp c1 c2)
- = HsIf exp (convertOpFormsLCmd c1) (convertOpFormsLCmd c2)
+convertOpFormsCmd (HsIf f exp c1 c2)
+ = HsIf f exp (convertOpFormsLCmd c1) (convertOpFormsLCmd c2)
convertOpFormsCmd (HsLet binds cmd)
= HsLet binds (convertOpFormsLCmd cmd)
methodNamesCmd (HsPar c) = methodNamesLCmd c
-methodNamesCmd (HsIf _ c1 c2)
+methodNamesCmd (HsIf _ _ c1 c2)
= methodNamesLCmd c1 `plusFV` methodNamesLCmd c2 `addOneFV` choiceAName
methodNamesCmd (HsLet _ c) = methodNamesLCmd c
its interface (although we could).
b) It might be GHC.Real.fromRational, or GHC.Num.fromInteger
- These are seen as "used" by the renamer (if -XNoImplicitPrelude)
+ These are seen as "used" by the renamer (if -XRebindableSyntax)
is on), but the typechecker may discard their uses
if in fact the in-scope fromRational is GHC.Read.fromRational,
(see tcPat.tcOverloadedLit), and the typechecker sees that the type
newMethodFromName origin name inst_ty
= do { id <- tcLookupId name
-- Use tcLookupId not tcLookupGlobalId; the method is almost
- -- always a class op, but with -XNoImplicitPrelude GHC is
+ -- always a class op, but with -XRebindableSyntax GHC is
-- meant to find whatever thing is in scope, and that may
-- be an ordinary function.
%* *
%************************************************************************
-Suppose we are doing the -XNoImplicitPrelude thing, and we encounter
+Suppose we are doing the -XRebindableSyntax thing, and we encounter
a do-expression. We have to find (>>) in the current environment, which is
done by the rename. Then we have to check that it has the same type as
Control.Monad.(>>). Or, more precisely, a compatible type. One 'customer' had
\begin{code}
module TcArrows ( tcProc ) where
-import {-# SOURCE #-} TcExpr( tcMonoExpr, tcInferRho )
+import {-# SOURCE #-} TcExpr( tcMonoExpr, tcInferRho, tcSyntaxOp )
import HsSyn
import TcMatches
mc_body = mc_body }
mc_body body res_ty' = tcGuardedCmd env body stk res_ty'
-tc_cmd env (HsIf pred b1 b2) res_ty
- = do { pred' <- tcMonoExpr pred boolTy
- ; b1' <- tcCmd env b1 res_ty
- ; b2' <- tcCmd env b2 res_ty
- ; return (HsIf pred' b1' b2')
+tc_cmd env (HsIf mb_fun pred b1 b2) (stack_ty,res_ty)
+ = do { pred_ty <- newFlexiTyVarTy openTypeKind
+ ; b_ty <- newFlexiTyVarTy openTypeKind
+ ; let if_ty = mkFunTys [pred_ty, b_ty, b_ty] res_ty
+ ; mb_fun' <- case mb_fun of
+ Nothing -> return Nothing
+ Just fun -> liftM Just (tcSyntaxOp IfOrigin fun if_ty)
+ ; pred' <- tcMonoExpr pred pred_ty
+ ; b1' <- tcCmd env b1 (stack_ty,b_ty)
+ ; b2' <- tcCmd env b2 (stack_ty,b_ty)
+ ; return (HsIf mb_fun' pred' b1' b2')
}
-------------------------------------------
match_ctxt = MC { mc_what = CaseAlt,
mc_body = tcBody }
-tcExpr (HsIf pred b1 b2) res_ty
- = do { pred' <- tcMonoExpr pred boolTy
- ; b1' <- tcMonoExpr b1 res_ty
- ; b2' <- tcMonoExpr b2 res_ty
- ; return (HsIf pred' b1' b2') }
+tcExpr (HsIf Nothing pred b1 b2) res_ty -- Ordinary 'if'
+ = do { pred' <- tcMonoExpr pred boolTy
+ ; b1' <- tcMonoExpr b1 res_ty
+ ; b2' <- tcMonoExpr b2 res_ty
+ ; return (HsIf Nothing pred' b1' b2') }
+
+tcExpr (HsIf (Just fun) pred b1 b2) res_ty -- Rebindable syntax
+ = do { pred_ty <- newFlexiTyVarTy openTypeKind
+ ; b_ty <- newFlexiTyVarTy openTypeKind
+ ; let if_ty = mkFunTys [pred_ty, b_ty, b_ty] res_ty
+ ; fun' <- tcSyntaxOp IfOrigin fun if_ty
+ ; pred' <- tcMonoExpr pred pred_ty
+ ; b1' <- tcMonoExpr b1 b_ty
+ ; b2' <- tcMonoExpr b2 b_ty
+ ; return (HsIf (Just fun') pred' b1' b2') }
tcExpr (HsDo do_or_lc stmts body _) res_ty
= tcDoStmts do_or_lc stmts body res_ty
zonkMatchGroup env ms `thenM` \ new_ms ->
returnM (HsCase new_expr new_ms)
-zonkExpr env (HsIf e1 e2 e3)
- = zonkLExpr env e1 `thenM` \ new_e1 ->
- zonkLExpr env e2 `thenM` \ new_e2 ->
- zonkLExpr env e3 `thenM` \ new_e3 ->
- returnM (HsIf new_e1 new_e2 new_e3)
+zonkExpr env (HsIf e0 e1 e2 e3)
+ = do { new_e0 <- fmapMaybeM (zonkExpr env) e0
+ ; new_e1 <- zonkLExpr env e1
+ ; new_e2 <- zonkLExpr env e2
+ ; new_e3 <- zonkLExpr env e3
+ ; returnM (HsIf new_e0 new_e1 new_e2 new_e3) }
zonkExpr env (HsLet binds expr)
= zonkLocalBinds env binds `thenM` \ (new_env, new_binds) ->
zonk_pat env (NPat lit mb_neg eq_expr)
= do { lit' <- zonkOverLit env lit
- ; mb_neg' <- case mb_neg of
- Nothing -> return Nothing
- Just neg -> do { neg' <- zonkExpr env neg
- ; return (Just neg') }
+ ; mb_neg' <- fmapMaybeM (zonkExpr env) mb_neg
; eq_expr' <- zonkExpr env eq_expr
; return (env, NPat lit' mb_neg' eq_expr') }
| StandAloneDerivOrigin -- Typechecking stand-alone deriving
| DefaultOrigin -- Typechecking a default decl
| DoOrigin -- Arising from a do expression
+ | IfOrigin -- Arising from an if statement
| ProcOrigin -- Arising from a proc expression
| AnnOrigin -- An annotation
pprO PatSigOrigin = ptext (sLit "a pattern type signature")
pprO PatOrigin = ptext (sLit "a pattern")
pprO ViewPatOrigin = ptext (sLit "a view pattern")
+pprO IfOrigin = ptext (sLit "an if statement")
pprO (LiteralOrigin lit) = hsep [ptext (sLit "the literal"), quotes (ppr lit)]
pprO (ArithSeqOrigin seq) = hsep [ptext (sLit "the arithmetic sequence"), quotes (ppr seq)]
pprO (PArrSeqOrigin seq) = hsep [ptext (sLit "the parallel array sequence"), quotes (ppr seq)]
<entry><option>-XImplicitPrelude</option></entry>
</row>
<row>
+ <entry><option>-XRebindableSyntax</option></entry>
+ <entry>Employ <link linkend="rebindable-syntax">rebindable syntax</link></entry>
+ <entry>dynamic</entry>
+ <entry><option>-XNoRebindableSyntax</option></entry>
+ </row>
+ <row>
<entry><option>-XNoMonomorphismRestriction</option></entry>
<entry>Disable the <link linkend="monomorphism">monomorphism restriction</link></entry>
<entry>dynamic</entry>
hierarchy. It completely defeats that purpose if the
literal "1" means "<literal>Prelude.fromInteger
1</literal>", which is what the Haskell Report specifies.
- So the <option>-XNoImplicitPrelude</option>
- flag <emphasis>also</emphasis> causes
+ So the <option>-XRebindableSyntax</option>
+ flag causes
the following pieces of built-in syntax to refer to
<emphasis>whatever is in scope</emphasis>, not the Prelude
versions:
</para></listitem>
<listitem>
+ <para>Conditionals (e.g. "<literal>if</literal> e1 <literal>then</literal> e2 <literal>else</literal> e3")
+ means "<literal>ifThenElse</literal> e1 e2 e3". However <literal>case</literal> expressions are unaffected.
+ </para></listitem>
+
+ <listitem>
<para>"Do" notation is translated using whatever
functions <literal>(>>=)</literal>,
<literal>(>>)</literal>, and <literal>fail</literal>,
to use this, ask!
</para></listitem>
</itemizedlist>
+<option>-XRebindableSyntax</option> implies <option>-XNoImplicitPrelude</option>.
+</para>
+<para>
In all cases (apart from arrow notation), the static semantics should be that of the desugared form,
even if that is a little unexpected. For example, the
static semantics of the literal <literal>368</literal>
projects / ghc-hetmet.git / commitdiff