2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Desugaring arrow commands
9 module DsArrows ( dsProcExpr ) where
11 #include "HsVersions.h"
20 -- NB: The desugarer, which straddles the source and Core worlds, sometimes
21 -- needs to see source types (newtypes etc), and sometimes not
22 -- So WATCH OUT; check each use of split*Ty functions.
23 -- Sigh. This is a pain.
25 import {-# SOURCE #-} DsExpr ( dsExpr, dsLExpr, dsLocalBinds )
48 data DsCmdEnv = DsCmdEnv {
49 meth_binds :: [CoreBind],
50 arr_id, compose_id, first_id, app_id, choice_id, loop_id :: CoreExpr
53 mkCmdEnv :: SyntaxTable Id -> DsM DsCmdEnv
55 = dsSyntaxTable ids `thenDs` \ (meth_binds, ds_meths) ->
57 meth_binds = meth_binds,
58 arr_id = Var (lookupEvidence ds_meths arrAName),
59 compose_id = Var (lookupEvidence ds_meths composeAName),
60 first_id = Var (lookupEvidence ds_meths firstAName),
61 app_id = Var (lookupEvidence ds_meths appAName),
62 choice_id = Var (lookupEvidence ds_meths choiceAName),
63 loop_id = Var (lookupEvidence ds_meths loopAName)
66 bindCmdEnv :: DsCmdEnv -> CoreExpr -> CoreExpr
67 bindCmdEnv ids body = foldr Let body (meth_binds ids)
69 -- arr :: forall b c. (b -> c) -> a b c
70 do_arr :: DsCmdEnv -> Type -> Type -> CoreExpr -> CoreExpr
71 do_arr ids b_ty c_ty f = mkApps (arr_id ids) [Type b_ty, Type c_ty, f]
73 -- (>>>) :: forall b c d. a b c -> a c d -> a b d
74 do_compose :: DsCmdEnv -> Type -> Type -> Type ->
75 CoreExpr -> CoreExpr -> CoreExpr
76 do_compose ids b_ty c_ty d_ty f g
77 = mkApps (compose_id ids) [Type b_ty, Type c_ty, Type d_ty, f, g]
79 -- first :: forall b c d. a b c -> a (b,d) (c,d)
80 do_first :: DsCmdEnv -> Type -> Type -> Type -> CoreExpr -> CoreExpr
81 do_first ids b_ty c_ty d_ty f
82 = mkApps (first_id ids) [Type b_ty, Type c_ty, Type d_ty, f]
84 -- app :: forall b c. a (a b c, b) c
85 do_app :: DsCmdEnv -> Type -> Type -> CoreExpr
86 do_app ids b_ty c_ty = mkApps (app_id ids) [Type b_ty, Type c_ty]
88 -- (|||) :: forall b d c. a b d -> a c d -> a (Either b c) d
89 -- note the swapping of d and c
90 do_choice :: DsCmdEnv -> Type -> Type -> Type ->
91 CoreExpr -> CoreExpr -> CoreExpr
92 do_choice ids b_ty c_ty d_ty f g
93 = mkApps (choice_id ids) [Type b_ty, Type d_ty, Type c_ty, f, g]
95 -- loop :: forall b d c. a (b,d) (c,d) -> a b c
96 -- note the swapping of d and c
97 do_loop :: DsCmdEnv -> Type -> Type -> Type -> CoreExpr -> CoreExpr
98 do_loop ids b_ty c_ty d_ty f
99 = mkApps (loop_id ids) [Type b_ty, Type d_ty, Type c_ty, f]
101 -- map_arrow (f :: b -> c) (g :: a c d) = arr f >>> g :: a b d
102 do_map_arrow :: DsCmdEnv -> Type -> Type -> Type ->
103 CoreExpr -> CoreExpr -> CoreExpr
104 do_map_arrow ids b_ty c_ty d_ty f c
105 = do_compose ids b_ty c_ty d_ty (do_arr ids b_ty c_ty f) c
107 mkFailExpr :: HsMatchContext Id -> Type -> DsM CoreExpr
109 = mkErrorAppDs pAT_ERROR_ID ty (matchContextErrString ctxt)
111 -- construct CoreExpr for \ (a :: a_ty, b :: b_ty) -> b
112 mkSndExpr :: Type -> Type -> DsM CoreExpr
114 = newSysLocalDs a_ty `thenDs` \ a_var ->
115 newSysLocalDs b_ty `thenDs` \ b_var ->
116 newSysLocalDs (mkCorePairTy a_ty b_ty) `thenDs` \ pair_var ->
117 returnDs (Lam pair_var
118 (coreCasePair pair_var a_var b_var (Var b_var)))
121 Build case analysis of a tuple. This cannot be done in the DsM monad,
122 because the list of variables is typically not yet defined.
125 -- coreCaseTuple [u1..] v [x1..xn] body
126 -- = case v of v { (x1, .., xn) -> body }
127 -- But the matching may be nested if the tuple is very big
129 coreCaseTuple :: UniqSupply -> Id -> [Id] -> CoreExpr -> CoreExpr
130 coreCaseTuple uniqs scrut_var vars body
131 = mkTupleCase uniqs vars body scrut_var (Var scrut_var)
133 coreCasePair :: Id -> Id -> Id -> CoreExpr -> CoreExpr
134 coreCasePair scrut_var var1 var2 body
135 = Case (Var scrut_var) scrut_var (exprType body)
136 [(DataAlt (tupleCon Boxed 2), [var1, var2], body)]
140 mkCorePairTy :: Type -> Type -> Type
141 mkCorePairTy t1 t2 = mkCoreTupTy [t1, t2]
143 mkCorePairExpr :: CoreExpr -> CoreExpr -> CoreExpr
144 mkCorePairExpr e1 e2 = mkCoreTup [e1, e2]
147 The input is divided into a local environment, which is a flat tuple
148 (unless it's too big), and a stack, each element of which is paired
149 with the stack in turn. In general, the input has the form
151 (...((x1,...,xn),s1),...sk)
153 where xi are the environment values, and si the ones on the stack,
154 with s1 being the "top", the first one to be matched with a lambda.
157 envStackType :: [Id] -> [Type] -> Type
158 envStackType ids stack_tys = foldl mkCorePairTy (mkTupleType ids) stack_tys
160 ----------------------------------------------
163 -- (...((x1,...,xn),s1),...sk)
165 buildEnvStack :: [Id] -> [Id] -> CoreExpr
166 buildEnvStack env_ids stack_ids
167 = foldl mkCorePairExpr (mkTupleExpr env_ids) (map Var stack_ids)
169 ----------------------------------------------
172 -- \ (...((x1,...,xn),s1),...sk) -> e
175 -- case zk of (zk-1,sk) ->
177 -- case z1 of (z0,s1) ->
178 -- case z0 of (x1,...,xn) ->
181 matchEnvStack :: [Id] -- x1..xn
185 matchEnvStack env_ids stack_ids body
186 = newUniqueSupply `thenDs` \ uniqs ->
187 newSysLocalDs (mkTupleType env_ids) `thenDs` \ tup_var ->
188 matchVarStack tup_var stack_ids
189 (coreCaseTuple uniqs tup_var env_ids body)
192 ----------------------------------------------
195 -- \ (...(z0,s1),...sk) -> e
198 -- case zk of (zk-1,sk) ->
200 -- case z1 of (z0,s1) ->
203 matchVarStack :: Id -- z0
207 matchVarStack env_id [] body
208 = returnDs (Lam env_id body)
209 matchVarStack env_id (stack_id:stack_ids) body
210 = newSysLocalDs (mkCorePairTy (idType env_id) (idType stack_id))
211 `thenDs` \ pair_id ->
212 matchVarStack pair_id stack_ids
213 (coreCasePair pair_id env_id stack_id body)
217 mkHsTupleExpr :: [HsExpr Id] -> HsExpr Id
218 mkHsTupleExpr [e] = e
219 mkHsTupleExpr es = ExplicitTuple (map noLoc es) Boxed
221 mkHsPairExpr :: HsExpr Id -> HsExpr Id -> HsExpr Id
222 mkHsPairExpr e1 e2 = mkHsTupleExpr [e1, e2]
224 mkHsEnvStackExpr :: [Id] -> [Id] -> HsExpr Id
225 mkHsEnvStackExpr env_ids stack_ids
226 = foldl mkHsPairExpr (mkHsTupleExpr (map HsVar env_ids)) (map HsVar stack_ids)
229 Translation of arrow abstraction
233 -- A | xs |- c :: [] t' ---> c'
234 -- --------------------------
235 -- A |- proc p -> c :: a t t' ---> arr (\ p -> (xs)) >>> c'
237 -- where (xs) is the tuple of variables bound by p
243 dsProcExpr pat (L _ (HsCmdTop cmd [] cmd_ty ids))
244 = mkCmdEnv ids `thenDs` \ meth_ids ->
246 locals = mkVarSet (collectPatBinders pat)
248 dsfixCmd meth_ids locals [] cmd_ty cmd
249 `thenDs` \ (core_cmd, free_vars, env_ids) ->
251 env_ty = mkTupleType env_ids
253 mkFailExpr ProcExpr env_ty `thenDs` \ fail_expr ->
254 selectSimpleMatchVarL pat `thenDs` \ var ->
255 matchSimply (Var var) ProcExpr pat (mkTupleExpr env_ids) fail_expr
256 `thenDs` \ match_code ->
258 pat_ty = hsLPatType pat
259 proc_code = do_map_arrow meth_ids pat_ty env_ty cmd_ty
263 returnDs (bindCmdEnv meth_ids proc_code)
266 Translation of command judgements of the form
268 A | xs |- c :: [ts] t
271 dsLCmd ids local_vars env_ids stack res_ty cmd
272 = dsCmd ids local_vars env_ids stack res_ty (unLoc cmd)
274 dsCmd :: DsCmdEnv -- arrow combinators
275 -> IdSet -- set of local vars available to this command
276 -> [Id] -- list of vars in the input to this command
277 -- This is typically fed back,
278 -- so don't pull on it too early
279 -> [Type] -- type of the stack
280 -> Type -- return type of the command
281 -> HsCmd Id -- command to desugar
282 -> DsM (CoreExpr, -- desugared expression
283 IdSet) -- set of local vars that occur free
285 -- A |- f :: a (t*ts) t'
287 -- -----------------------------
288 -- A | xs |- f -< arg :: [ts] t'
290 -- ---> arr (\ ((xs)*ts) -> (arg*ts)) >>> f
292 dsCmd ids local_vars env_ids stack res_ty
293 (HsArrApp arrow arg arrow_ty HsFirstOrderApp _)
295 (a_arg_ty, _res_ty') = tcSplitAppTy arrow_ty
296 (_a_ty, arg_ty) = tcSplitAppTy a_arg_ty
297 env_ty = mkTupleType env_ids
299 dsLExpr arrow `thenDs` \ core_arrow ->
300 dsLExpr arg `thenDs` \ core_arg ->
301 mappM newSysLocalDs stack `thenDs` \ stack_ids ->
302 matchEnvStack env_ids stack_ids
303 (foldl mkCorePairExpr core_arg (map Var stack_ids))
304 `thenDs` \ core_make_arg ->
305 returnDs (do_map_arrow ids
306 (envStackType env_ids stack)
311 exprFreeVars core_arg `intersectVarSet` local_vars)
313 -- A, xs |- f :: a (t*ts) t'
315 -- ------------------------------
316 -- A | xs |- f -<< arg :: [ts] t'
318 -- ---> arr (\ ((xs)*ts) -> (f,(arg*ts))) >>> app
320 dsCmd ids local_vars env_ids stack res_ty
321 (HsArrApp arrow arg arrow_ty HsHigherOrderApp _)
323 (a_arg_ty, _res_ty') = tcSplitAppTy arrow_ty
324 (_a_ty, arg_ty) = tcSplitAppTy a_arg_ty
325 env_ty = mkTupleType env_ids
327 dsLExpr arrow `thenDs` \ core_arrow ->
328 dsLExpr arg `thenDs` \ core_arg ->
329 mappM newSysLocalDs stack `thenDs` \ stack_ids ->
330 matchEnvStack env_ids stack_ids
331 (mkCorePairExpr core_arrow
332 (foldl mkCorePairExpr core_arg (map Var stack_ids)))
333 `thenDs` \ core_make_pair ->
334 returnDs (do_map_arrow ids
335 (envStackType env_ids stack)
336 (mkCorePairTy arrow_ty arg_ty)
339 (do_app ids arg_ty res_ty),
340 (exprFreeVars core_arrow `unionVarSet` exprFreeVars core_arg)
341 `intersectVarSet` local_vars)
343 -- A | ys |- c :: [t:ts] t'
345 -- ------------------------
346 -- A | xs |- c e :: [ts] t'
348 -- ---> arr (\ ((xs)*ts) -> let z = e in (((ys),z)*ts)) >>> c
350 dsCmd ids local_vars env_ids stack res_ty (HsApp cmd arg)
351 = dsLExpr arg `thenDs` \ core_arg ->
353 arg_ty = exprType core_arg
354 stack' = arg_ty:stack
356 dsfixCmd ids local_vars stack' res_ty cmd
357 `thenDs` \ (core_cmd, free_vars, env_ids') ->
358 mappM newSysLocalDs stack `thenDs` \ stack_ids ->
359 newSysLocalDs arg_ty `thenDs` \ arg_id ->
360 -- push the argument expression onto the stack
362 core_body = bindNonRec arg_id core_arg
363 (buildEnvStack env_ids' (arg_id:stack_ids))
365 -- match the environment and stack against the input
366 matchEnvStack env_ids stack_ids core_body
367 `thenDs` \ core_map ->
368 returnDs (do_map_arrow ids
369 (envStackType env_ids stack)
370 (envStackType env_ids' stack')
374 (exprFreeVars core_arg `intersectVarSet` local_vars)
375 `unionVarSet` free_vars)
377 -- A | ys |- c :: [ts] t'
378 -- -----------------------------------------------
379 -- A | xs |- \ p1 ... pk -> c :: [t1:...:tk:ts] t'
381 -- ---> arr (\ ((((xs), p1), ... pk)*ts) -> ((ys)*ts)) >>> c
383 dsCmd ids local_vars env_ids stack res_ty
384 (HsLam (MatchGroup [L _ (Match pats _ (GRHSs [L _ (GRHS [] body)] _ ))] _))
386 pat_vars = mkVarSet (collectPatsBinders pats)
387 local_vars' = local_vars `unionVarSet` pat_vars
388 stack' = drop (length pats) stack
390 dsfixCmd ids local_vars' stack' res_ty body
391 `thenDs` \ (core_body, free_vars, env_ids') ->
392 mappM newSysLocalDs stack `thenDs` \ stack_ids ->
394 -- the expression is built from the inside out, so the actions
395 -- are presented in reverse order
398 (actual_ids, stack_ids') = splitAt (length pats) stack_ids
399 -- build a new environment, plus what's left of the stack
400 core_expr = buildEnvStack env_ids' stack_ids'
401 in_ty = envStackType env_ids stack
402 in_ty' = envStackType env_ids' stack'
404 mkFailExpr LambdaExpr in_ty' `thenDs` \ fail_expr ->
405 -- match the patterns against the top of the old stack
406 matchSimplys (map Var actual_ids) LambdaExpr pats core_expr fail_expr
407 `thenDs` \ match_code ->
408 -- match the old environment and stack against the input
409 matchEnvStack env_ids stack_ids match_code
410 `thenDs` \ select_code ->
411 returnDs (do_map_arrow ids in_ty in_ty' res_ty select_code core_body,
412 free_vars `minusVarSet` pat_vars)
414 dsCmd ids local_vars env_ids stack res_ty (HsPar cmd)
415 = dsLCmd ids local_vars env_ids stack res_ty cmd
417 -- A, xs |- e :: Bool
418 -- A | xs1 |- c1 :: [ts] t
419 -- A | xs2 |- c2 :: [ts] t
420 -- ----------------------------------------
421 -- A | xs |- if e then c1 else c2 :: [ts] t
423 -- ---> arr (\ ((xs)*ts) ->
424 -- if e then Left ((xs1)*ts) else Right ((xs2)*ts)) >>>
427 dsCmd ids local_vars env_ids stack res_ty (HsIf cond then_cmd else_cmd)
428 = dsLExpr cond `thenDs` \ core_cond ->
429 dsfixCmd ids local_vars stack res_ty then_cmd
430 `thenDs` \ (core_then, fvs_then, then_ids) ->
431 dsfixCmd ids local_vars stack res_ty else_cmd
432 `thenDs` \ (core_else, fvs_else, else_ids) ->
433 mappM newSysLocalDs stack `thenDs` \ stack_ids ->
434 dsLookupTyCon eitherTyConName `thenDs` \ either_con ->
435 dsLookupDataCon leftDataConName `thenDs` \ left_con ->
436 dsLookupDataCon rightDataConName `thenDs` \ right_con ->
438 left_expr ty1 ty2 e = mkConApp left_con [Type ty1, Type ty2, e]
439 right_expr ty1 ty2 e = mkConApp right_con [Type ty1, Type ty2, e]
441 in_ty = envStackType env_ids stack
442 then_ty = envStackType then_ids stack
443 else_ty = envStackType else_ids stack
444 sum_ty = mkTyConApp either_con [then_ty, else_ty]
445 fvs_cond = exprFreeVars core_cond `intersectVarSet` local_vars
447 matchEnvStack env_ids stack_ids
448 (mkIfThenElse core_cond
449 (left_expr then_ty else_ty (buildEnvStack then_ids stack_ids))
450 (right_expr then_ty else_ty (buildEnvStack else_ids stack_ids)))
451 `thenDs` \ core_if ->
452 returnDs(do_map_arrow ids in_ty sum_ty res_ty
454 (do_choice ids then_ty else_ty res_ty core_then core_else),
455 fvs_cond `unionVarSet` fvs_then `unionVarSet` fvs_else)
458 Case commands are treated in much the same way as if commands
459 (see above) except that there are more alternatives. For example
461 case e of { p1 -> c1; p2 -> c2; p3 -> c3 }
465 arr (\ ((xs)*ts) -> case e of
466 p1 -> (Left (Left (xs1)*ts))
467 p2 -> Left ((Right (xs2)*ts))
468 p3 -> Right ((xs3)*ts)) >>>
471 The idea is to extract the commands from the case, build a balanced tree
472 of choices, and replace the commands with expressions that build tagged
473 tuples, obtaining a case expression that can be desugared normally.
474 To build all this, we use quadruples decribing segments of the list of
475 case bodies, containing the following fields:
476 1. an IdSet containing the environment variables free in the case bodies
477 2. a list of expressions of the form (Left|Right)* ((xs)*ts), to be put
478 into the case replacing the commands
479 3. a sum type that is the common type of these expressions, and also the
480 input type of the arrow
481 4. a CoreExpr for an arrow built by combining the translated command
485 dsCmd ids local_vars env_ids stack res_ty (HsCase exp (MatchGroup matches match_ty))
486 = dsLExpr exp `thenDs` \ core_exp ->
487 mappM newSysLocalDs stack `thenDs` \ stack_ids ->
489 -- Extract and desugar the leaf commands in the case, building tuple
490 -- expressions that will (after tagging) replace these leaves
493 leaves = concatMap leavesMatch matches
494 make_branch (leaf, bound_vars)
495 = dsfixCmd ids (local_vars `unionVarSet` bound_vars) stack res_ty leaf
496 `thenDs` \ (core_leaf, fvs, leaf_ids) ->
497 returnDs (fvs `minusVarSet` bound_vars,
498 [noLoc $ mkHsEnvStackExpr leaf_ids stack_ids],
499 envStackType leaf_ids stack,
502 mappM make_branch leaves `thenDs` \ branches ->
503 dsLookupTyCon eitherTyConName `thenDs` \ either_con ->
504 dsLookupDataCon leftDataConName `thenDs` \ left_con ->
505 dsLookupDataCon rightDataConName `thenDs` \ right_con ->
507 left_id = HsVar (dataConWrapId left_con)
508 right_id = HsVar (dataConWrapId right_con)
509 left_expr ty1 ty2 e = noLoc $ HsApp (noLoc $ HsWrap (mkWpTyApps [ty1, ty2]) left_id ) e
510 right_expr ty1 ty2 e = noLoc $ HsApp (noLoc $ HsWrap (mkWpTyApps [ty1, ty2]) right_id) e
512 -- Prefix each tuple with a distinct series of Left's and Right's,
513 -- in a balanced way, keeping track of the types.
515 merge_branches (fvs1, builds1, in_ty1, core_exp1)
516 (fvs2, builds2, in_ty2, core_exp2)
517 = (fvs1 `unionVarSet` fvs2,
518 map (left_expr in_ty1 in_ty2) builds1 ++
519 map (right_expr in_ty1 in_ty2) builds2,
520 mkTyConApp either_con [in_ty1, in_ty2],
521 do_choice ids in_ty1 in_ty2 res_ty core_exp1 core_exp2)
522 (fvs_alts, leaves', sum_ty, core_choices)
523 = foldb merge_branches branches
525 -- Replace the commands in the case with these tagged tuples,
526 -- yielding a HsExpr Id we can feed to dsExpr.
528 (_, matches') = mapAccumL (replaceLeavesMatch res_ty) leaves' matches
529 in_ty = envStackType env_ids stack
530 fvs_exp = exprFreeVars core_exp `intersectVarSet` local_vars
532 pat_ty = funArgTy match_ty
533 match_ty' = mkFunTy pat_ty sum_ty
534 -- Note that we replace the HsCase result type by sum_ty,
535 -- which is the type of matches'
537 dsExpr (HsCase exp (MatchGroup matches' match_ty')) `thenDs` \ core_body ->
538 matchEnvStack env_ids stack_ids core_body
539 `thenDs` \ core_matches ->
540 returnDs(do_map_arrow ids in_ty sum_ty res_ty core_matches core_choices,
541 fvs_exp `unionVarSet` fvs_alts)
543 -- A | ys |- c :: [ts] t
544 -- ----------------------------------
545 -- A | xs |- let binds in c :: [ts] t
547 -- ---> arr (\ ((xs)*ts) -> let binds in ((ys)*ts)) >>> c
549 dsCmd ids local_vars env_ids stack res_ty (HsLet binds body)
551 defined_vars = mkVarSet (map unLoc (collectLocalBinders binds))
552 local_vars' = local_vars `unionVarSet` defined_vars
554 dsfixCmd ids local_vars' stack res_ty body
555 `thenDs` \ (core_body, free_vars, env_ids') ->
556 mappM newSysLocalDs stack `thenDs` \ stack_ids ->
557 -- build a new environment, plus the stack, using the let bindings
558 dsLocalBinds binds (buildEnvStack env_ids' stack_ids)
559 `thenDs` \ core_binds ->
560 -- match the old environment and stack against the input
561 matchEnvStack env_ids stack_ids core_binds
562 `thenDs` \ core_map ->
563 returnDs (do_map_arrow ids
564 (envStackType env_ids stack)
565 (envStackType env_ids' stack)
569 exprFreeVars core_binds `intersectVarSet` local_vars)
571 dsCmd ids local_vars env_ids [] res_ty (HsDo _ctxt stmts body _)
572 = dsCmdDo ids local_vars env_ids res_ty stmts body
574 -- A |- e :: forall e. a1 (e*ts1) t1 -> ... an (e*tsn) tn -> a (e*ts) t
575 -- A | xs |- ci :: [tsi] ti
576 -- -----------------------------------
577 -- A | xs |- (|e c1 ... cn|) :: [ts] t ---> e [t_xs] c1 ... cn
579 dsCmd _ids local_vars env_ids _stack _res_ty (HsArrForm op _ args)
581 env_ty = mkTupleType env_ids
583 dsLExpr op `thenDs` \ core_op ->
584 mapAndUnzipDs (dsTrimCmdArg local_vars env_ids) args
585 `thenDs` \ (core_args, fv_sets) ->
586 returnDs (mkApps (App core_op (Type env_ty)) core_args,
587 unionVarSets fv_sets)
589 -- A | ys |- c :: [ts] t (ys <= xs)
590 -- ---------------------
591 -- A | xs |- c :: [ts] t ---> arr_ts (\ (xs) -> (ys)) >>> c
594 :: IdSet -- set of local vars available to this command
595 -> [Id] -- list of vars in the input to this command
596 -> LHsCmdTop Id -- command argument to desugar
597 -> DsM (CoreExpr, -- desugared expression
598 IdSet) -- set of local vars that occur free
599 dsTrimCmdArg local_vars env_ids (L _ (HsCmdTop cmd stack cmd_ty ids))
600 = mkCmdEnv ids `thenDs` \ meth_ids ->
601 dsfixCmd meth_ids local_vars stack cmd_ty cmd
602 `thenDs` \ (core_cmd, free_vars, env_ids') ->
603 mappM newSysLocalDs stack `thenDs` \ stack_ids ->
604 matchEnvStack env_ids stack_ids (buildEnvStack env_ids' stack_ids)
605 `thenDs` \ trim_code ->
607 in_ty = envStackType env_ids stack
608 in_ty' = envStackType env_ids' stack
609 arg_code = if env_ids' == env_ids then core_cmd else
610 do_map_arrow meth_ids in_ty in_ty' cmd_ty trim_code core_cmd
612 returnDs (bindCmdEnv meth_ids arg_code, free_vars)
614 -- Given A | xs |- c :: [ts] t, builds c with xs fed back.
615 -- Typically needs to be prefixed with arr (\p -> ((xs)*ts))
618 :: DsCmdEnv -- arrow combinators
619 -> IdSet -- set of local vars available to this command
620 -> [Type] -- type of the stack
621 -> Type -- return type of the command
622 -> LHsCmd Id -- command to desugar
623 -> DsM (CoreExpr, -- desugared expression
624 IdSet, -- set of local vars that occur free
625 [Id]) -- set as a list, fed back
626 dsfixCmd ids local_vars stack cmd_ty cmd
627 = fixDs (\ ~(_,_,env_ids') ->
628 dsLCmd ids local_vars env_ids' stack cmd_ty cmd
629 `thenDs` \ (core_cmd, free_vars) ->
630 returnDs (core_cmd, free_vars, varSetElems free_vars))
634 Translation of command judgements of the form
636 A | xs |- do { ss } :: [] t
640 dsCmdDo :: DsCmdEnv -- arrow combinators
641 -> IdSet -- set of local vars available to this statement
642 -> [Id] -- list of vars in the input to this statement
643 -- This is typically fed back,
644 -- so don't pull on it too early
645 -> Type -- return type of the statement
646 -> [LStmt Id] -- statements to desugar
647 -> LHsExpr Id -- body
648 -> DsM (CoreExpr, -- desugared expression
649 IdSet) -- set of local vars that occur free
651 -- A | xs |- c :: [] t
652 -- --------------------------
653 -- A | xs |- do { c } :: [] t
655 dsCmdDo ids local_vars env_ids res_ty [] body
656 = dsLCmd ids local_vars env_ids [] res_ty body
658 dsCmdDo ids local_vars env_ids res_ty (stmt:stmts) body
660 bound_vars = mkVarSet (map unLoc (collectLStmtBinders stmt))
661 local_vars' = local_vars `unionVarSet` bound_vars
663 fixDs (\ ~(_,_,env_ids') ->
664 dsCmdDo ids local_vars' env_ids' res_ty stmts body
665 `thenDs` \ (core_stmts, fv_stmts) ->
666 returnDs (core_stmts, fv_stmts, varSetElems fv_stmts))
667 `thenDs` \ (core_stmts, fv_stmts, env_ids') ->
668 dsCmdLStmt ids local_vars env_ids env_ids' stmt
669 `thenDs` \ (core_stmt, fv_stmt) ->
670 returnDs (do_compose ids
671 (mkTupleType env_ids)
672 (mkTupleType env_ids')
679 A statement maps one local environment to another, and is represented
680 as an arrow from one tuple type to another. A statement sequence is
681 translated to a composition of such arrows.
683 dsCmdLStmt ids local_vars env_ids out_ids cmd
684 = dsCmdStmt ids local_vars env_ids out_ids (unLoc cmd)
687 :: DsCmdEnv -- arrow combinators
688 -> IdSet -- set of local vars available to this statement
689 -> [Id] -- list of vars in the input to this statement
690 -- This is typically fed back,
691 -- so don't pull on it too early
692 -> [Id] -- list of vars in the output of this statement
693 -> Stmt Id -- statement to desugar
694 -> DsM (CoreExpr, -- desugared expression
695 IdSet) -- set of local vars that occur free
697 -- A | xs1 |- c :: [] t
698 -- A | xs' |- do { ss } :: [] t'
699 -- ------------------------------
700 -- A | xs |- do { c; ss } :: [] t'
702 -- ---> arr (\ (xs) -> ((xs1),(xs'))) >>> first c >>>
705 dsCmdStmt ids local_vars env_ids out_ids (ExprStmt cmd _ c_ty)
706 = dsfixCmd ids local_vars [] c_ty cmd
707 `thenDs` \ (core_cmd, fv_cmd, env_ids1) ->
708 matchEnvStack env_ids []
709 (mkCorePairExpr (mkTupleExpr env_ids1) (mkTupleExpr out_ids))
710 `thenDs` \ core_mux ->
712 in_ty = mkTupleType env_ids
713 in_ty1 = mkTupleType env_ids1
714 out_ty = mkTupleType out_ids
715 before_c_ty = mkCorePairTy in_ty1 out_ty
716 after_c_ty = mkCorePairTy c_ty out_ty
718 mkSndExpr c_ty out_ty `thenDs` \ snd_fn ->
719 returnDs (do_map_arrow ids in_ty before_c_ty out_ty core_mux $
720 do_compose ids before_c_ty after_c_ty out_ty
721 (do_first ids in_ty1 c_ty out_ty core_cmd) $
722 do_arr ids after_c_ty out_ty snd_fn,
723 extendVarSetList fv_cmd out_ids)
726 -- A | xs1 |- c :: [] t
727 -- A | xs' |- do { ss } :: [] t' xs2 = xs' - defs(p)
728 -- -----------------------------------
729 -- A | xs |- do { p <- c; ss } :: [] t'
731 -- ---> arr (\ (xs) -> ((xs1),(xs2))) >>> first c >>>
732 -- arr (\ (p, (xs2)) -> (xs')) >>> ss
734 -- It would be simpler and more consistent to do this using second,
735 -- but that's likely to be defined in terms of first.
737 dsCmdStmt ids local_vars env_ids out_ids (BindStmt pat cmd _ _)
738 = dsfixCmd ids local_vars [] (hsLPatType pat) cmd
739 `thenDs` \ (core_cmd, fv_cmd, env_ids1) ->
741 pat_ty = hsLPatType pat
742 pat_vars = mkVarSet (collectPatBinders pat)
743 env_ids2 = varSetElems (mkVarSet out_ids `minusVarSet` pat_vars)
744 env_ty2 = mkTupleType env_ids2
747 -- multiplexing function
748 -- \ (xs) -> ((xs1),(xs2))
750 matchEnvStack env_ids []
751 (mkCorePairExpr (mkTupleExpr env_ids1) (mkTupleExpr env_ids2))
752 `thenDs` \ core_mux ->
754 -- projection function
755 -- \ (p, (xs2)) -> (zs)
757 newSysLocalDs env_ty2 `thenDs` \ env_id ->
758 newUniqueSupply `thenDs` \ uniqs ->
760 after_c_ty = mkCorePairTy pat_ty env_ty2
761 out_ty = mkTupleType out_ids
762 body_expr = coreCaseTuple uniqs env_id env_ids2 (mkTupleExpr out_ids)
764 mkFailExpr (StmtCtxt DoExpr) out_ty `thenDs` \ fail_expr ->
765 selectSimpleMatchVarL pat `thenDs` \ pat_id ->
766 matchSimply (Var pat_id) (StmtCtxt DoExpr) pat body_expr fail_expr
767 `thenDs` \ match_code ->
768 newSysLocalDs after_c_ty `thenDs` \ pair_id ->
770 proj_expr = Lam pair_id (coreCasePair pair_id pat_id env_id match_code)
773 -- put it all together
775 in_ty = mkTupleType env_ids
776 in_ty1 = mkTupleType env_ids1
777 in_ty2 = mkTupleType env_ids2
778 before_c_ty = mkCorePairTy in_ty1 in_ty2
780 returnDs (do_map_arrow ids in_ty before_c_ty out_ty core_mux $
781 do_compose ids before_c_ty after_c_ty out_ty
782 (do_first ids in_ty1 pat_ty in_ty2 core_cmd) $
783 do_arr ids after_c_ty out_ty proj_expr,
784 fv_cmd `unionVarSet` (mkVarSet out_ids `minusVarSet` pat_vars))
786 -- A | xs' |- do { ss } :: [] t
787 -- --------------------------------------
788 -- A | xs |- do { let binds; ss } :: [] t
790 -- ---> arr (\ (xs) -> let binds in (xs')) >>> ss
792 dsCmdStmt ids local_vars env_ids out_ids (LetStmt binds)
793 -- build a new environment using the let bindings
794 = dsLocalBinds binds (mkTupleExpr out_ids) `thenDs` \ core_binds ->
795 -- match the old environment against the input
796 matchEnvStack env_ids [] core_binds `thenDs` \ core_map ->
798 (mkTupleType env_ids)
799 (mkTupleType out_ids)
801 exprFreeVars core_binds `intersectVarSet` local_vars)
803 -- A | ys |- do { ss; returnA -< ((xs1), (ys2)) } :: [] ...
804 -- A | xs' |- do { ss' } :: [] t
805 -- ------------------------------------
806 -- A | xs |- do { rec ss; ss' } :: [] t
808 -- xs1 = xs' /\ defs(ss)
809 -- xs2 = xs' - defs(ss)
810 -- ys1 = ys - defs(ss)
811 -- ys2 = ys /\ defs(ss)
813 -- ---> arr (\(xs) -> ((ys1),(xs2))) >>>
814 -- first (loop (arr (\((ys1),~(ys2)) -> (ys)) >>> ss)) >>>
815 -- arr (\((xs1),(xs2)) -> (xs')) >>> ss'
817 dsCmdStmt ids local_vars env_ids out_ids (RecStmt stmts later_ids rec_ids rhss binds)
818 = let -- ToDo: ****** binds not desugared; ROSS PLEASE FIX ********
819 env2_id_set = mkVarSet out_ids `minusVarSet` mkVarSet later_ids
820 env2_ids = varSetElems env2_id_set
821 env2_ty = mkTupleType env2_ids
824 -- post_loop_fn = \((later_ids),(env2_ids)) -> (out_ids)
826 newUniqueSupply `thenDs` \ uniqs ->
827 newSysLocalDs env2_ty `thenDs` \ env2_id ->
829 later_ty = mkTupleType later_ids
830 post_pair_ty = mkCorePairTy later_ty env2_ty
831 post_loop_body = coreCaseTuple uniqs env2_id env2_ids (mkTupleExpr out_ids)
833 matchEnvStack later_ids [env2_id] post_loop_body
834 `thenDs` \ post_loop_fn ->
838 dsRecCmd ids local_vars stmts later_ids rec_ids rhss
839 `thenDs` \ (core_loop, env1_id_set, env1_ids) ->
841 -- pre_loop_fn = \(env_ids) -> ((env1_ids),(env2_ids))
844 env1_ty = mkTupleType env1_ids
845 pre_pair_ty = mkCorePairTy env1_ty env2_ty
846 pre_loop_body = mkCorePairExpr (mkTupleExpr env1_ids)
847 (mkTupleExpr env2_ids)
850 matchEnvStack env_ids [] pre_loop_body
851 `thenDs` \ pre_loop_fn ->
853 -- arr pre_loop_fn >>> first (loop (...)) >>> arr post_loop_fn
856 env_ty = mkTupleType env_ids
857 out_ty = mkTupleType out_ids
858 core_body = do_map_arrow ids env_ty pre_pair_ty out_ty
860 (do_compose ids pre_pair_ty post_pair_ty out_ty
861 (do_first ids env1_ty later_ty env2_ty
863 (do_arr ids post_pair_ty out_ty
866 returnDs (core_body, env1_id_set `unionVarSet` env2_id_set)
868 -- loop (arr (\ ((env1_ids), ~(rec_ids)) -> (env_ids)) >>>
870 -- arr (\ (out_ids) -> ((later_ids),(rhss))) >>>
872 dsRecCmd ids local_vars stmts later_ids rec_ids rhss
874 rec_id_set = mkVarSet rec_ids
875 out_ids = varSetElems (mkVarSet later_ids `unionVarSet` rec_id_set)
876 out_ty = mkTupleType out_ids
877 local_vars' = local_vars `unionVarSet` rec_id_set
880 -- mk_pair_fn = \ (out_ids) -> ((later_ids),(rhss))
882 mappM dsExpr rhss `thenDs` \ core_rhss ->
884 later_tuple = mkTupleExpr later_ids
885 later_ty = mkTupleType later_ids
886 rec_tuple = mkBigCoreTup core_rhss
887 rec_ty = mkTupleType rec_ids
888 out_pair = mkCorePairExpr later_tuple rec_tuple
889 out_pair_ty = mkCorePairTy later_ty rec_ty
891 matchEnvStack out_ids [] out_pair
892 `thenDs` \ mk_pair_fn ->
896 dsfixCmdStmts ids local_vars' out_ids stmts
897 `thenDs` \ (core_stmts, fv_stmts, env_ids) ->
899 -- squash_pair_fn = \ ((env1_ids), ~(rec_ids)) -> (env_ids)
901 newSysLocalDs rec_ty `thenDs` \ rec_id ->
903 env1_id_set = fv_stmts `minusVarSet` rec_id_set
904 env1_ids = varSetElems env1_id_set
905 env1_ty = mkTupleType env1_ids
906 in_pair_ty = mkCorePairTy env1_ty rec_ty
907 core_body = mkBigCoreTup (map selectVar env_ids)
910 | v `elemVarSet` rec_id_set
911 = mkTupleSelector rec_ids v rec_id (Var rec_id)
914 matchEnvStack env1_ids [rec_id] core_body
915 `thenDs` \ squash_pair_fn ->
917 -- loop (arr squash_pair_fn >>> ss >>> arr mk_pair_fn)
920 env_ty = mkTupleType env_ids
921 core_loop = do_loop ids env1_ty later_ty rec_ty
922 (do_map_arrow ids in_pair_ty env_ty out_pair_ty
924 (do_compose ids env_ty out_ty out_pair_ty
926 (do_arr ids out_ty out_pair_ty mk_pair_fn)))
928 returnDs (core_loop, env1_id_set, env1_ids)
931 A sequence of statements (as in a rec) is desugared to an arrow between
936 :: DsCmdEnv -- arrow combinators
937 -> IdSet -- set of local vars available to this statement
938 -> [Id] -- output vars of these statements
939 -> [LStmt Id] -- statements to desugar
940 -> DsM (CoreExpr, -- desugared expression
941 IdSet, -- set of local vars that occur free
944 dsfixCmdStmts ids local_vars out_ids stmts
945 = fixDs (\ ~(_,_,env_ids) ->
946 dsCmdStmts ids local_vars env_ids out_ids stmts
947 `thenDs` \ (core_stmts, fv_stmts) ->
948 returnDs (core_stmts, fv_stmts, varSetElems fv_stmts))
951 :: DsCmdEnv -- arrow combinators
952 -> IdSet -- set of local vars available to this statement
953 -> [Id] -- list of vars in the input to these statements
954 -> [Id] -- output vars of these statements
955 -> [LStmt Id] -- statements to desugar
956 -> DsM (CoreExpr, -- desugared expression
957 IdSet) -- set of local vars that occur free
959 dsCmdStmts ids local_vars env_ids out_ids [stmt]
960 = dsCmdLStmt ids local_vars env_ids out_ids stmt
962 dsCmdStmts ids local_vars env_ids out_ids (stmt:stmts)
964 bound_vars = mkVarSet (map unLoc (collectLStmtBinders stmt))
965 local_vars' = local_vars `unionVarSet` bound_vars
967 dsfixCmdStmts ids local_vars' out_ids stmts
968 `thenDs` \ (core_stmts, fv_stmts, env_ids') ->
969 dsCmdLStmt ids local_vars env_ids env_ids' stmt
970 `thenDs` \ (core_stmt, fv_stmt) ->
971 returnDs (do_compose ids
972 (mkTupleType env_ids)
973 (mkTupleType env_ids')
974 (mkTupleType out_ids)
981 Match a list of expressions against a list of patterns, left-to-right.
984 matchSimplys :: [CoreExpr] -- Scrutinees
985 -> HsMatchContext Name -- Match kind
986 -> [LPat Id] -- Patterns they should match
987 -> CoreExpr -- Return this if they all match
988 -> CoreExpr -- Return this if they don't
990 matchSimplys [] _ctxt [] result_expr _fail_expr = returnDs result_expr
991 matchSimplys (exp:exps) ctxt (pat:pats) result_expr fail_expr
992 = matchSimplys exps ctxt pats result_expr fail_expr
993 `thenDs` \ match_code ->
994 matchSimply exp ctxt pat match_code fail_expr
997 List of leaf expressions, with set of variables bound in each
1000 leavesMatch :: LMatch Id -> [(LHsExpr Id, IdSet)]
1001 leavesMatch (L _ (Match pats _ (GRHSs grhss binds)))
1003 defined_vars = mkVarSet (collectPatsBinders pats)
1005 mkVarSet (map unLoc (collectLocalBinders binds))
1008 mkVarSet (map unLoc (collectLStmtsBinders stmts))
1009 `unionVarSet` defined_vars)
1010 | L _ (GRHS stmts expr) <- grhss]
1013 Replace the leaf commands in a match
1017 :: Type -- new result type
1018 -> [LHsExpr Id] -- replacement leaf expressions of that type
1019 -> LMatch Id -- the matches of a case command
1020 -> ([LHsExpr Id],-- remaining leaf expressions
1021 LMatch Id) -- updated match
1022 replaceLeavesMatch res_ty leaves (L loc (Match pat mt (GRHSs grhss binds)))
1024 (leaves', grhss') = mapAccumL replaceLeavesGRHS leaves grhss
1026 (leaves', L loc (Match pat mt (GRHSs grhss' binds)))
1029 :: [LHsExpr Id] -- replacement leaf expressions of that type
1030 -> LGRHS Id -- rhss of a case command
1031 -> ([LHsExpr Id],-- remaining leaf expressions
1032 LGRHS Id) -- updated GRHS
1033 replaceLeavesGRHS (leaf:leaves) (L loc (GRHS stmts rhs))
1034 = (leaves, L loc (GRHS stmts leaf))
1037 Balanced fold of a non-empty list.
1040 foldb :: (a -> a -> a) -> [a] -> a
1041 foldb _ [] = error "foldb of empty list"
1043 foldb f xs = foldb f (fold_pairs xs)
1046 fold_pairs [x] = [x]
1047 fold_pairs (x1:x2:xs) = f x1 x2:fold_pairs xs