2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
4 \section[DsUtils]{Utilities for desugaring}
6 This module exports some utility functions of no great interest.
9 #include "HsVersions.h"
12 CanItFail(..), EquationInfo(..), MatchResult(..),
14 combineGRHSMatchResults,
17 mkCoAlgCaseMatchResult,
18 mkAppDs, mkConDs, mkPrimDs, mkErrorAppDs,
20 mkCoPrimCaseMatchResult,
31 IMPORT_DELOOPER(DsLoop) ( match, matchSimply )
33 import HsSyn ( HsExpr(..), OutPat(..), HsLit(..),
34 Match, HsBinds, Stmt, Qual, PolyType, ArithSeqInfo )
35 import TcHsSyn ( TypecheckedPat(..) )
36 import DsHsSyn ( outPatType )
41 import CoreUtils ( coreExprType, mkCoreIfThenElse )
42 import PprStyle ( PprStyle(..) )
43 import PrelVals ( iRREFUT_PAT_ERROR_ID, voidId )
44 import Pretty ( ppShow )
45 import Id ( idType, dataConArgTys, mkTupleCon,
47 DataCon(..), DictVar(..), Id(..), GenId )
48 import Literal ( Literal(..) )
49 import TyCon ( mkTupleTyCon, isNewTyCon, tyConDataCons )
50 import Type ( mkTyVarTys, mkRhoTy, mkForAllTys, mkFunTys,
51 mkTheta, isUnboxedType, applyTyCon, getAppTyCon
53 import TysWiredIn ( voidTy )
54 import UniqSet ( mkUniqSet, minusUniqSet, uniqSetToList, UniqSet(..) )
55 import Util ( panic, assertPanic, pprTrace{-ToDo:rm-} )
56 import PprCore{-ToDo:rm-}
57 --import PprType--ToDo:rm
58 import Pretty--ToDo:rm
60 import Unique--ToDo:rm
64 %************************************************************************
66 %* type synonym EquationInfo and access functions for its pieces *
68 %************************************************************************
69 \subsection[EquationInfo-synonym]{@EquationInfo@: a useful synonym}
71 The ``equation info'' used by @match@ is relatively complicated and
72 worthy of a type synonym and a few handy functions.
77 [TypecheckedPat] -- the patterns for an eqn
78 MatchResult -- Encapsulates the guards and bindings
85 Type -- Type of argument expression
87 (CoreExpr -> CoreExpr)
88 -- Takes a expression to plug in at the
89 -- failure point(s). The expression should
92 DsMatchContext -- The context info is used when producing warnings
93 -- about shadowed patterns. It's the context
94 -- of the *first* thing matched in this group.
95 -- Should perhaps be a list of them all!
97 data CanItFail = CanFail | CantFail
99 orFail CantFail CantFail = CantFail
103 mkCoLetsMatchResult :: [CoreBinding] -> MatchResult -> MatchResult
104 mkCoLetsMatchResult binds (MatchResult can_it_fail ty body_fn cxt)
105 = MatchResult can_it_fail ty (\body -> mkCoLetsAny binds (body_fn body)) cxt
107 mkGuardedMatchResult :: CoreExpr -> MatchResult -> DsM MatchResult
108 mkGuardedMatchResult pred_expr (MatchResult can_it_fail ty body_fn cxt)
109 = returnDs (MatchResult CanFail
111 (\fail -> mkCoreIfThenElse pred_expr (body_fn fail) fail)
115 mkCoPrimCaseMatchResult :: Id -- Scrutinee
116 -> [(Literal, MatchResult)] -- Alternatives
118 mkCoPrimCaseMatchResult var alts
119 = newSysLocalDs (idType var) `thenDs` \ wild ->
120 returnDs (MatchResult CanFail
125 ((_,MatchResult _ ty1 _ cxt1) : _) = alts
127 mk_case alts wild fail_expr
128 = Case (Var var) (PrimAlts final_alts (BindDefault wild fail_expr))
130 final_alts = [ (lit, body_fn fail_expr)
131 | (lit, MatchResult _ _ body_fn _) <- alts
135 mkCoAlgCaseMatchResult :: Id -- Scrutinee
136 -> [(DataCon, [Id], MatchResult)] -- Alternatives
139 mkCoAlgCaseMatchResult var alts
140 | isNewTyCon tycon -- newtype case; use a let
141 = ASSERT( newtype_sanity )
142 returnDs (mkCoLetsMatchResult [coercion_bind] match_result)
144 | otherwise -- datatype case
145 = -- Find all the constructors in the type which aren't
146 -- explicitly mentioned in the alternatives:
147 case un_mentioned_constructors of
148 [] -> -- All constructors mentioned, so no default needed
149 returnDs (MatchResult can_any_alt_fail
151 (mk_case alts (\ignore -> NoDefault))
154 [con] -> -- Just one constructor missing, so add a case for it
155 -- We need to build new locals for the args of the constructor,
156 -- and figuring out their types is somewhat tiresome.
158 arg_tys = dataConArgTys con tycon_arg_tys
160 newSysLocalsDs arg_tys `thenDs` \ arg_ids ->
162 -- Now we are ready to construct the new alternative
164 new_alt = (con, arg_ids, MatchResult CanFail ty1 id NoMatchContext)
166 returnDs (MatchResult CanFail
168 (mk_case (new_alt:alts) (\ignore -> NoDefault))
171 other -> -- Many constructors missing, so use a default case
172 newSysLocalDs scrut_ty `thenDs` \ wild ->
173 returnDs (MatchResult CanFail
175 (mk_case alts (\fail_expr -> BindDefault wild fail_expr))
179 scrut_ty = idType var
180 (tycon, tycon_arg_tys) = --pprTrace "CoAlgCase:" (pprType PprDebug scrut_ty) $
184 (con_id, arg_ids, match_result) = head alts
185 arg_id = head arg_ids
186 coercion_bind = NonRec arg_id (Coerce (CoerceOut con_id)
189 newtype_sanity = null (tail alts) && null (tail arg_ids)
191 -- Stuff for data types
192 data_cons = tyConDataCons tycon
194 un_mentioned_constructors
195 = uniqSetToList (mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- alts] )
197 match_results = [match_result | (_,_,match_result) <- alts]
198 (MatchResult _ ty1 _ cxt1 : _) = match_results
199 can_any_alt_fail = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ _ _ <- match_results]
201 mk_case alts deflt_fn fail_expr
202 = Case (Var var) (AlgAlts final_alts (deflt_fn fail_expr))
204 final_alts = [ (con, args, body_fn fail_expr)
205 | (con, args, MatchResult _ _ body_fn _) <- alts
209 combineMatchResults :: MatchResult -> MatchResult -> DsM MatchResult
210 combineMatchResults (MatchResult CanFail ty1 body_fn1 cxt1)
211 (MatchResult can_it_fail2 ty2 body_fn2 cxt2)
212 = mkFailurePair ty1 `thenDs` \ (bind_fn, duplicatable_expr) ->
214 new_body_fn1 = \body1 -> Let (bind_fn body1) (body_fn1 duplicatable_expr)
215 new_body_fn2 = \body2 -> new_body_fn1 (body_fn2 body2)
217 returnDs (MatchResult can_it_fail2 ty1 new_body_fn2 cxt1)
219 combineMatchResults match_result1@(MatchResult CantFail ty body_fn1 cxt1)
221 = returnDs match_result1
224 -- The difference in combineGRHSMatchResults is that there is no
225 -- need to let-bind to avoid code duplication
226 combineGRHSMatchResults :: MatchResult -> MatchResult -> DsM MatchResult
227 combineGRHSMatchResults (MatchResult CanFail ty1 body_fn1 cxt1)
228 (MatchResult can_it_fail ty2 body_fn2 cxt2)
229 = returnDs (MatchResult can_it_fail ty1 (\ body -> body_fn1 (body_fn2 body)) cxt1)
231 combineGRHSMatchResults match_result1 match_result2
232 = -- Delegate to avoid duplication of code
233 combineMatchResults match_result1 match_result2
236 %************************************************************************
238 \subsection[dsExprToAtom]{Take an expression and produce an atom}
240 %************************************************************************
243 dsExprToAtom :: CoreExpr -- The argument expression
244 -> (CoreArg -> DsM CoreExpr) -- Something taking the argument *atom*,
245 -- and delivering an expression E
246 -> DsM CoreExpr -- Either E or let x=arg-expr in E
248 dsExprToAtom (Var v) continue_with = continue_with (VarArg v)
249 dsExprToAtom (Lit v) continue_with = continue_with (LitArg v)
251 dsExprToAtom arg_expr continue_with
253 ty = coreExprType arg_expr
255 newSysLocalDs ty `thenDs` \ arg_id ->
256 continue_with (VarArg arg_id) `thenDs` \ body ->
259 then Case arg_expr (PrimAlts [] (BindDefault arg_id body))
260 else Let (NonRec arg_id arg_expr) body
263 dsExprsToAtoms :: [CoreExpr]
264 -> ([CoreArg] -> DsM CoreExpr)
267 dsExprsToAtoms [] continue_with
270 dsExprsToAtoms (arg:args) continue_with
271 = dsExprToAtom arg $ \ arg_atom ->
272 dsExprsToAtoms args $ \ arg_atoms ->
273 continue_with (arg_atom:arg_atoms)
276 %************************************************************************
278 \subsection{Desugarer's versions of some Core functions}
280 %************************************************************************
283 mkAppDs :: CoreExpr -> [Type] -> [CoreExpr] -> DsM CoreExpr
284 mkConDs :: Id -> [Type] -> [CoreExpr] -> DsM CoreExpr
285 mkPrimDs :: PrimOp -> [Type] -> [CoreExpr] -> DsM CoreExpr
287 mkAppDs fun tys arg_exprs
288 = dsExprsToAtoms arg_exprs $ \ vals ->
289 returnDs (mkApp fun [] tys vals)
291 mkConDs con tys arg_exprs
292 = dsExprsToAtoms arg_exprs $ \ vals ->
293 returnDs (mkCon con [] tys vals)
295 mkPrimDs op tys arg_exprs
296 = dsExprsToAtoms arg_exprs $ \ vals ->
297 returnDs (mkPrim op [] tys vals)
301 showForErr :: Outputable a => a -> String -- Boring but useful
302 showForErr thing = ppShow 80 (ppr PprForUser thing)
304 mkErrorAppDs :: Id -- The error function
305 -> Type -- Type to which it should be applied
306 -> String -- The error message string to pass
309 mkErrorAppDs err_id ty msg
310 = getSrcLocDs `thenDs` \ (file, line) ->
312 full_msg = file ++ "|" ++ line ++ "|" ++msg
313 msg_lit = NoRepStr (_PK_ full_msg)
315 returnDs (mkApp (Var err_id) [] [ty] [LitArg msg_lit])
318 %************************************************************************
320 \subsection[mkSelectorBind]{Make a selector bind}
322 %************************************************************************
324 This is used in various places to do with lazy patterns.
325 For each binder $b$ in the pattern, we create a binding:
327 b = case v of pat' -> b'
329 where pat' is pat with each binder b cloned into b'.
331 ToDo: making these bindings should really depend on whether there's
332 much work to be done per binding. If the pattern is complex, it
333 should be de-mangled once, into a tuple (and then selected from).
334 Otherwise the demangling can be in-line in the bindings (as here).
336 Boring! Boring! One error message per binder. The above ToDo is
337 even more helpful. Something very similar happens for pattern-bound
341 mkSelectorBinds :: [TyVar] -- Variables wrt which the pattern is polymorphic
342 -> TypecheckedPat -- The pattern
343 -> [(Id,Id)] -- Monomorphic and polymorphic binders for
345 -> CoreExpr -- Expression to which the pattern is bound
346 -> DsM [(Id,CoreExpr)]
348 mkSelectorBinds tyvars pat locals_and_globals val_expr
349 = if is_simple_tuple_pat pat then
350 mkTupleBind tyvars [] locals_and_globals val_expr
352 mkErrorAppDs iRREFUT_PAT_ERROR_ID res_ty "" `thenDs` \ error_msg ->
353 matchSimply val_expr pat res_ty local_tuple error_msg `thenDs` \ tuple_expr ->
354 mkTupleBind tyvars [] locals_and_globals tuple_expr
356 locals = [local | (local, _) <- locals_and_globals]
357 local_tuple = mkTupleExpr locals
358 res_ty = coreExprType local_tuple
360 is_simple_tuple_pat (TuplePat ps) = all is_var_pat ps
361 is_simple_tuple_pat other = False
363 is_var_pat (VarPat v) = True
364 is_var_pat other = False -- Even wild-card patterns aren't acceptable
367 We're about to match against some patterns. We want to make some
368 @Ids@ to use as match variables. If a pattern has an @Id@ readily at
369 hand, which should indeed be bound to the pattern as a whole, then use it;
370 otherwise, make one up.
372 selectMatchVars :: [TypecheckedPat] -> DsM [Id]
374 = mapDs var_from_pat_maybe pats
376 var_from_pat_maybe (VarPat var) = returnDs var
377 var_from_pat_maybe (AsPat var pat) = returnDs var
378 var_from_pat_maybe (LazyPat pat) = var_from_pat_maybe pat
379 var_from_pat_maybe other_pat
380 = newSysLocalDs (outPatType other_pat) -- OK, better make up one...
384 mkTupleBind :: [TyVar] -- Abstract wrt these...
385 -> [DictVar] -- ... and these
387 -> [(Id, Id)] -- Local, global pairs, equal in number
388 -- to the size of the tuple. The types
389 -- of the globals is the generalisation of
390 -- the corresp local, wrt the tyvars and dicts
392 -> CoreExpr -- Expr whose value is a tuple; the expression
393 -- may mention the tyvars and dicts
395 -> DsM [(Id, CoreExpr)] -- Bindings for the globals
400 mkTupleBind tyvars dicts [(l1,g1), ..., (ln,gn)] tup_expr
402 If $n=1$, the result is:
404 g1 = /\ tyvars -> \ dicts -> rhs
406 Otherwise, the result is:
408 tup = /\ tyvars -> \ dicts -> tup_expr
409 g1 = /\ tyvars -> \ dicts -> case (tup tyvars dicts) of
415 mkTupleBind tyvars dicts [(local,global)] tuple_expr
416 = returnDs [(global, mkLam tyvars dicts tuple_expr)]
422 mkTupleBind tyvars dicts local_global_prs tuple_expr
423 = --pprTrace "mkTupleBind:\n" (ppAboves [ppCat (map (pprId PprShowAll) locals), ppCat (map (pprId PprShowAll) globals), {-ppr PprDebug local_tuple, pprType PprDebug res_ty,-} ppr PprDebug tuple_expr]) $
425 newSysLocalDs tuple_var_ty `thenDs` \ tuple_var ->
427 zipWithDs (mk_selector (Var tuple_var))
429 [(0::Int) .. (length local_global_prs - 1)]
430 `thenDs` \ tup_selectors ->
432 (tuple_var, mkLam tyvars dicts tuple_expr)
436 locals, globals :: [Id]
437 locals = [local | (local,global) <- local_global_prs]
438 globals = [global | (local,global) <- local_global_prs]
440 no_of_binders = length local_global_prs
441 tyvar_tys = mkTyVarTys tyvars
445 = mkForAllTys tyvars $
447 applyTyCon (mkTupleTyCon no_of_binders)
450 theta = mkTheta (map idType dicts)
452 mk_selector :: CoreExpr -> (Id, Id) -> Int -> DsM (Id, CoreExpr)
454 mk_selector tuple_var_expr (local, global) which_local
455 = mapDs duplicateLocalDs locals{-the whole bunch-} `thenDs` \ binders ->
457 selected = binders !! which_local
463 (mkValApp (mkTyApp tuple_var_expr tyvar_tys)
470 @mkTupleExpr@ builds a tuple; the inverse to @mkTupleSelector@. If it
471 has only one element, it is the identity function.
473 mkTupleExpr :: [Id] -> CoreExpr
475 mkTupleExpr [] = Con (mkTupleCon 0) []
476 mkTupleExpr [id] = Var id
477 mkTupleExpr ids = mkCon (mkTupleCon (length ids))
480 [ VarArg i | i <- ids ]
484 @mkTupleSelector@ builds a selector which scrutises the given
485 expression and extracts the one name from the list given.
486 If you want the no-shadowing rule to apply, the caller
487 is responsible for making sure that none of these names
490 If there is just one id in the ``tuple'', then the selector is
494 mkTupleSelector :: CoreExpr -- Scrutinee
495 -> [Id] -- The tuple args
496 -> Id -- The selected one
499 mkTupleSelector expr [] the_var = panic "mkTupleSelector"
501 mkTupleSelector expr [var] should_be_the_same_var
502 = ASSERT(var == should_be_the_same_var)
505 mkTupleSelector expr vars the_var
506 = Case expr (AlgAlts [(mkTupleCon arity, vars, Var the_var)]
513 %************************************************************************
515 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
517 %************************************************************************
519 Generally, we handle pattern matching failure like this: let-bind a
520 fail-variable, and use that variable if the thing fails:
522 let fail.33 = error "Help"
533 If the case can't fail, then there'll be no mention of fail.33, and the
534 simplifier will later discard it.
537 If it can fail in only one way, then the simplifier will inline it.
540 Only if it is used more than once will the let-binding remain.
543 There's a problem when the result of the case expression is of
544 unboxed type. Then the type of fail.33 is unboxed too, and
545 there is every chance that someone will change the let into a case:
551 which is of course utterly wrong. Rather than drop the condition that
552 only boxed types can be let-bound, we just turn the fail into a function
553 for the primitive case:
555 let fail.33 :: Void -> Int#
556 fail.33 = \_ -> error "Help"
565 Now fail.33 is a function, so it can be let-bound.
568 mkFailurePair :: Type -- Result type of the whole case expression
569 -> DsM (CoreExpr -> CoreBinding,
570 -- Binds the newly-created fail variable
571 -- to either the expression or \ _ -> expression
572 CoreExpr) -- Either the fail variable, or fail variable
573 -- applied to unit tuple
576 = newFailLocalDs (mkFunTys [voidTy] ty) `thenDs` \ fail_fun_var ->
577 newSysLocalDs voidTy `thenDs` \ fail_fun_arg ->
579 NonRec fail_fun_var (Lam (ValBinder fail_fun_arg) body),
580 App (Var fail_fun_var) (VarArg voidId))
583 = newFailLocalDs ty `thenDs` \ fail_var ->
584 returnDs (\ body -> NonRec fail_var body, Var fail_var)