DsArrows.hs 47.6 KB
Newer Older
Austin Seipp's avatar
Austin Seipp committed
1 2 3 4
{-
(c) The University of Glasgow 2006
(c) The GRASP/AQUA Project, Glasgow University, 1992-1998

Simon Marlow's avatar
Simon Marlow committed
5 6

Desugaring arrow commands
Austin Seipp's avatar
Austin Seipp committed
7
-}
8

9
{-# LANGUAGE CPP #-}
10
{-# LANGUAGE TypeFamilies #-}
Ian Lynagh's avatar
Ian Lynagh committed
11

12 13 14 15
module DsArrows ( dsProcExpr ) where

#include "HsVersions.h"

16 17
import GhcPrelude

Simon Marlow's avatar
Simon Marlow committed
18 19
import Match
import DsUtils
20 21
import DsMonad

22
import HsSyn    hiding (collectPatBinders, collectPatsBinders, collectLStmtsBinders, collectLStmtBinders, collectStmtBinders )
Simon Marlow's avatar
Simon Marlow committed
23
import TcHsSyn
Simon Marlow's avatar
Simon Marlow committed
24
import qualified HsUtils
25 26 27 28 29 30

-- NB: The desugarer, which straddles the source and Core worlds, sometimes
--     needs to see source types (newtypes etc), and sometimes not
--     So WATCH OUT; check each use of split*Ty functions.
-- Sigh.  This is a pain.

Richard Eisenberg's avatar
Richard Eisenberg committed
31
import {-# SOURCE #-} DsExpr ( dsExpr, dsLExpr, dsLExprNoLP, dsLocalBinds, dsSyntaxExpr )
32

Simon Marlow's avatar
Simon Marlow committed
33
import TcType
Richard Eisenberg's avatar
Richard Eisenberg committed
34
import Type ( splitPiTy )
35
import TcEvidence
36
import CoreSyn
Simon Marlow's avatar
Simon Marlow committed
37 38
import CoreFVs
import CoreUtils
39
import MkCore
40
import DsBinds (dsHsWrapper)
41

Simon Marlow's avatar
Simon Marlow committed
42
import Name
43
import Id
Richard Eisenberg's avatar
Richard Eisenberg committed
44
import ConLike
Simon Marlow's avatar
Simon Marlow committed
45 46 47
import TysWiredIn
import BasicTypes
import PrelNames
Ian Lynagh's avatar
Ian Lynagh committed
48
import Outputable
49
import Bag
Simon Marlow's avatar
Simon Marlow committed
50 51
import VarSet
import SrcLoc
Richard Eisenberg's avatar
Richard Eisenberg committed
52
import ListSetOps( assocMaybe )
53
import Data.List
niteria's avatar
niteria committed
54
import Util
niteria's avatar
niteria committed
55
import UniqDFM
David Feuer's avatar
David Feuer committed
56
import UniqSet
57 58

data DsCmdEnv = DsCmdEnv {
59
        arr_id, compose_id, first_id, app_id, choice_id, loop_id :: CoreExpr
60 61
    }

62
mkCmdEnv :: CmdSyntaxTable GhcTc -> DsM ([CoreBind], DsCmdEnv)
63 64 65
-- See Note [CmdSyntaxTable] in HsExpr
mkCmdEnv tc_meths
  = do { (meth_binds, prs) <- mapAndUnzipM mk_bind tc_meths
Richard Eisenberg's avatar
Richard Eisenberg committed
66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95

       -- NB: Some of these lookups might fail, but that's OK if the
       -- symbol is never used. That's why we use Maybe first and then
       -- panic. An eager panic caused trouble in typecheck/should_compile/tc192
       ; let the_arr_id     = assocMaybe prs arrAName
             the_compose_id = assocMaybe prs composeAName
             the_first_id   = assocMaybe prs firstAName
             the_app_id     = assocMaybe prs appAName
             the_choice_id  = assocMaybe prs choiceAName
             the_loop_id    = assocMaybe prs loopAName

           -- used as an argument in, e.g., do_premap
       ; check_lev_poly 3 the_arr_id

           -- used as an argument in, e.g., dsCmdStmt/BodyStmt
       ; check_lev_poly 5 the_compose_id

           -- used as an argument in, e.g., dsCmdStmt/BodyStmt
       ; check_lev_poly 4 the_first_id

           -- the result of the_app_id is used as an argument in, e.g.,
           -- dsCmd/HsCmdArrApp/HsHigherOrderApp
       ; check_lev_poly 2 the_app_id

           -- used as an argument in, e.g., HsCmdIf
       ; check_lev_poly 5 the_choice_id

           -- used as an argument in, e.g., RecStmt
       ; check_lev_poly 4 the_loop_id

96
       ; return (meth_binds, DsCmdEnv {
Richard Eisenberg's avatar
Richard Eisenberg committed
97 98 99 100 101 102
               arr_id     = Var (unmaybe the_arr_id arrAName),
               compose_id = Var (unmaybe the_compose_id composeAName),
               first_id   = Var (unmaybe the_first_id firstAName),
               app_id     = Var (unmaybe the_app_id appAName),
               choice_id  = Var (unmaybe the_choice_id choiceAName),
               loop_id    = Var (unmaybe the_loop_id loopAName)
103 104 105 106
             }) }
  where
    mk_bind (std_name, expr)
      = do { rhs <- dsExpr expr
Richard Eisenberg's avatar
Richard Eisenberg committed
107
           ; id <- newSysLocalDs (exprType rhs)  -- no check needed; these are functions
108
           ; return (NonRec id rhs, (std_name, id)) }
109

Richard Eisenberg's avatar
Richard Eisenberg committed
110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126
    unmaybe Nothing name = pprPanic "mkCmdEnv" (text "Not found:" <+> ppr name)
    unmaybe (Just id) _  = id

      -- returns the result type of a pi-type (that is, a forall or a function)
      -- Note that this result type may be ill-scoped.
    res_type :: Type -> Type
    res_type ty = res_ty
      where
        (_, res_ty) = splitPiTy ty

    check_lev_poly :: Int -- arity
                   -> Maybe Id -> DsM ()
    check_lev_poly _     Nothing = return ()
    check_lev_poly arity (Just id)
      = dsNoLevPoly (nTimes arity res_type (idType id))
          (text "In the result of the function" <+> quotes (ppr id))

127 128 129 130 131 132 133

-- arr :: forall b c. (b -> c) -> a b c
do_arr :: DsCmdEnv -> Type -> Type -> CoreExpr -> CoreExpr
do_arr ids b_ty c_ty f = mkApps (arr_id ids) [Type b_ty, Type c_ty, f]

-- (>>>) :: forall b c d. a b c -> a c d -> a b d
do_compose :: DsCmdEnv -> Type -> Type -> Type ->
134
                CoreExpr -> CoreExpr -> CoreExpr
135 136 137 138 139 140 141 142 143 144 145 146 147 148 149
do_compose ids b_ty c_ty d_ty f g
  = mkApps (compose_id ids) [Type b_ty, Type c_ty, Type d_ty, f, g]

-- first :: forall b c d. a b c -> a (b,d) (c,d)
do_first :: DsCmdEnv -> Type -> Type -> Type -> CoreExpr -> CoreExpr
do_first ids b_ty c_ty d_ty f
  = mkApps (first_id ids) [Type b_ty, Type c_ty, Type d_ty, f]

-- app :: forall b c. a (a b c, b) c
do_app :: DsCmdEnv -> Type -> Type -> CoreExpr
do_app ids b_ty c_ty = mkApps (app_id ids) [Type b_ty, Type c_ty]

-- (|||) :: forall b d c. a b d -> a c d -> a (Either b c) d
-- note the swapping of d and c
do_choice :: DsCmdEnv -> Type -> Type -> Type ->
150
                CoreExpr -> CoreExpr -> CoreExpr
151 152 153 154 155 156 157 158 159
do_choice ids b_ty c_ty d_ty f g
  = mkApps (choice_id ids) [Type b_ty, Type d_ty, Type c_ty, f, g]

-- loop :: forall b d c. a (b,d) (c,d) -> a b c
-- note the swapping of d and c
do_loop :: DsCmdEnv -> Type -> Type -> Type -> CoreExpr -> CoreExpr
do_loop ids b_ty c_ty d_ty f
  = mkApps (loop_id ids) [Type b_ty, Type d_ty, Type c_ty, f]

160 161 162
-- premap :: forall b c d. (b -> c) -> a c d -> a b d
-- premap f g = arr f >>> g
do_premap :: DsCmdEnv -> Type -> Type -> Type ->
163
                CoreExpr -> CoreExpr -> CoreExpr
164 165
do_premap ids b_ty c_ty d_ty f g
   = do_compose ids b_ty c_ty d_ty (do_arr ids b_ty c_ty f) g
166

167
mkFailExpr :: HsMatchContext Id -> Type -> DsM CoreExpr
168 169 170
mkFailExpr ctxt ty
  = mkErrorAppDs pAT_ERROR_ID ty (matchContextErrString ctxt)

171 172 173 174 175 176 177 178 179
-- construct CoreExpr for \ (a :: a_ty, b :: b_ty) -> a
mkFstExpr :: Type -> Type -> DsM CoreExpr
mkFstExpr a_ty b_ty = do
    a_var <- newSysLocalDs a_ty
    b_var <- newSysLocalDs b_ty
    pair_var <- newSysLocalDs (mkCorePairTy a_ty b_ty)
    return (Lam pair_var
               (coreCasePair pair_var a_var b_var (Var a_var)))

180 181
-- construct CoreExpr for \ (a :: a_ty, b :: b_ty) -> b
mkSndExpr :: Type -> Type -> DsM CoreExpr
182 183 184 185 186 187
mkSndExpr a_ty b_ty = do
    a_var <- newSysLocalDs a_ty
    b_var <- newSysLocalDs b_ty
    pair_var <- newSysLocalDs (mkCorePairTy a_ty b_ty)
    return (Lam pair_var
               (coreCasePair pair_var a_var b_var (Var b_var)))
188

Austin Seipp's avatar
Austin Seipp committed
189
{-
190 191
Build case analysis of a tuple.  This cannot be done in the DsM monad,
because the list of variables is typically not yet defined.
Austin Seipp's avatar
Austin Seipp committed
192
-}
193 194

-- coreCaseTuple [u1..] v [x1..xn] body
195
--      = case v of v { (x1, .., xn) -> body }
196 197 198
-- But the matching may be nested if the tuple is very big

coreCaseTuple :: UniqSupply -> Id -> [Id] -> CoreExpr -> CoreExpr
ross's avatar
ross committed
199 200
coreCaseTuple uniqs scrut_var vars body
  = mkTupleCase uniqs vars body scrut_var (Var scrut_var)
201

ross's avatar
ross committed
202 203
coreCasePair :: Id -> Id -> Id -> CoreExpr -> CoreExpr
coreCasePair scrut_var var1 var2 body
204
  = Case (Var scrut_var) scrut_var (exprType body)
205
         [(DataAlt (tupleDataCon Boxed 2), [var1, var2], body)]
206 207

mkCorePairTy :: Type -> Type -> Type
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
208
mkCorePairTy t1 t2 = mkBoxedTupleTy [t1, t2]
209 210 211

mkCorePairExpr :: CoreExpr -> CoreExpr -> CoreExpr
mkCorePairExpr e1 e2 = mkCoreTup [e1, e2]
212 213 214

mkCoreUnitExpr :: CoreExpr
mkCoreUnitExpr = mkCoreTup []
215

Austin Seipp's avatar
Austin Seipp committed
216
{-
217
The input is divided into a local environment, which is a flat tuple
218 219
(unless it's too big), and a stack, which is a right-nested pair.
In general, the input has the form
220

221
        ((x1,...,xn), (s1,...(sk,())...))
222 223 224

where xi are the environment values, and si the ones on the stack,
with s1 being the "top", the first one to be matched with a lambda.
Austin Seipp's avatar
Austin Seipp committed
225
-}
226

227 228 229 230 231 232 233 234 235 236
envStackType :: [Id] -> Type -> Type
envStackType ids stack_ty = mkCorePairTy (mkBigCoreVarTupTy ids) stack_ty

-- splitTypeAt n (t1,... (tn,t)...) = ([t1, ..., tn], t)
splitTypeAt :: Int -> Type -> ([Type], Type)
splitTypeAt n ty
  | n == 0 = ([], ty)
  | otherwise = case tcTyConAppArgs ty of
      [t, ty'] -> let (ts, ty_r) = splitTypeAt (n-1) ty' in (t:ts, ty_r)
      _ -> pprPanic "splitTypeAt" (ppr ty)
237 238

----------------------------------------------
239
--              buildEnvStack
240
--
241
--      ((x1,...,xn),stk)
242

243 244 245
buildEnvStack :: [Id] -> Id -> CoreExpr
buildEnvStack env_ids stack_id
  = mkCorePairExpr (mkBigCoreVarTup env_ids) (Var stack_id)
246 247

----------------------------------------------
248
--              matchEnvStack
249
--
250 251 252 253 254 255 256 257 258 259 260
--      \ ((x1,...,xn),stk) -> body
--      =>
--      \ pair ->
--      case pair of (tup,stk) ->
--      case tup of (x1,...,xn) ->
--      body

matchEnvStack   :: [Id]         -- x1..xn
                -> Id           -- stk
                -> CoreExpr     -- e
                -> DsM CoreExpr
261
matchEnvStack env_ids stack_id body = do
262 263
    uniqs <- newUniqueSupply
    tup_var <- newSysLocalDs (mkBigCoreVarTupTy env_ids)
264 265 266
    let match_env = coreCaseTuple uniqs tup_var env_ids body
    pair_id <- newSysLocalDs (mkCorePairTy (idType tup_var) (idType stack_id))
    return (Lam pair_id (coreCasePair pair_id tup_var stack_id match_env))
267

268
----------------------------------------------
269
--              matchEnv
270
--
271 272 273 274 275 276 277 278 279
--      \ (x1,...,xn) -> body
--      =>
--      \ tup ->
--      case tup of (x1,...,xn) ->
--      body

matchEnv :: [Id]        -- x1..xn
         -> CoreExpr    -- e
         -> DsM CoreExpr
280 281 282 283
matchEnv env_ids body = do
    uniqs <- newUniqueSupply
    tup_id <- newSysLocalDs (mkBigCoreVarTupTy env_ids)
    return (Lam tup_id (coreCaseTuple uniqs tup_id env_ids body))
284 285

----------------------------------------------
286
--              matchVarStack
287
--
288 289 290 291 292
--      case (x1, ...(xn, s)...) -> e
--      =>
--      case z0 of (x1,z1) ->
--      case zn-1 of (xn,s) ->
--      e
293 294 295 296 297 298
matchVarStack :: [Id] -> Id -> CoreExpr -> DsM (Id, CoreExpr)
matchVarStack [] stack_id body = return (stack_id, body)
matchVarStack (param_id:param_ids) stack_id body = do
    (tail_id, tail_code) <- matchVarStack param_ids stack_id body
    pair_id <- newSysLocalDs (mkCorePairTy (idType param_id) (idType tail_id))
    return (pair_id, coreCasePair pair_id param_id tail_id tail_code)
299

300
mkHsEnvStackExpr :: [Id] -> Id -> LHsExpr GhcTc
301 302
mkHsEnvStackExpr env_ids stack_id
  = mkLHsTupleExpr [mkLHsVarTuple env_ids, nlHsVar stack_id]
303

Austin Seipp's avatar
Austin Seipp committed
304
-- Translation of arrow abstraction
305

306
-- D; xs |-a c : () --> t'      ---> c'
307
-- --------------------------
308
-- D |- proc p -> c :: a t t'   ---> premap (\ p -> ((xs),())) c'
309
--
310
--              where (xs) is the tuple of variables bound by p
311 312

dsProcExpr
313 314
        :: LPat GhcTc
        -> LHsCmdTop GhcTc
315
        -> DsM CoreExpr
316
dsProcExpr pat (L _ (HsCmdTop (CmdTopTc _unitTy cmd_ty ids) cmd)) = do
317
    (meth_binds, meth_ids) <- mkCmdEnv ids
318
    let locals = mkVarSet (collectPatBinders pat)
319
    (core_cmd, _free_vars, env_ids) <- dsfixCmd meth_ids locals unitTy cmd_ty cmd
320
    let env_ty = mkBigCoreVarTupTy env_ids
321 322 323
    let env_stk_ty = mkCorePairTy env_ty unitTy
    let env_stk_expr = mkCorePairExpr (mkBigCoreVarTup env_ids) mkCoreUnitExpr
    fail_expr <- mkFailExpr ProcExpr env_stk_ty
324
    var <- selectSimpleMatchVarL pat
325
    match_code <- matchSimply (Var var) ProcExpr pat env_stk_expr fail_expr
326
    let pat_ty = hsLPatType pat
327
    let proc_code = do_premap meth_ids pat_ty env_stk_ty cmd_ty
328 329
                    (Lam var match_code)
                    core_cmd
330
    return (mkLets meth_binds proc_code)
331
dsProcExpr _ (L _ XCmdTop{}) = panic "dsProcExpr"
332

Austin Seipp's avatar
Austin Seipp committed
333
{-
334 335
Translation of a command judgement of the form

336
        D; xs |-a c : stk --> t
337 338

to an expression e such that
339

340
        D |- e :: a (xs, stk) t
Austin Seipp's avatar
Austin Seipp committed
341
-}
342

343
dsLCmd :: DsCmdEnv -> IdSet -> Type -> Type -> LHsCmd GhcTc -> [Id]
niteria's avatar
niteria committed
344
       -> DsM (CoreExpr, DIdSet)
345 346
dsLCmd ids local_vars stk_ty res_ty cmd env_ids
  = dsCmd ids local_vars stk_ty res_ty (unLoc cmd) env_ids
347

348 349 350 351
dsCmd   :: DsCmdEnv             -- arrow combinators
        -> IdSet                -- set of local vars available to this command
        -> Type                 -- type of the stack (right-nested tuple)
        -> Type                 -- return type of the command
352 353
        -> HsCmd GhcTc           -- command to desugar
        -> [Id]           -- list of vars in the input to this command
354 355 356
                                -- This is typically fed back,
                                -- so don't pull on it too early
        -> DsM (CoreExpr,       -- desugared expression
niteria's avatar
niteria committed
357
                DIdSet)         -- subset of local vars that occur free
358

359 360 361 362
-- D |- fun :: a t1 t2
-- D, xs |- arg :: t1
-- -----------------------------
-- D; xs |-a fun -< arg : stk --> t2
ross's avatar
ross committed
363
--
364
--              ---> premap (\ ((xs), _stk) -> arg) fun
365

366
dsCmd ids local_vars stack_ty res_ty
367
        (HsCmdArrApp arrow_ty arrow arg HsFirstOrderApp _)
368
        env_ids = do
369 370
    let
        (a_arg_ty, _res_ty') = tcSplitAppTy arrow_ty
ross's avatar
ross committed
371
        (_a_ty, arg_ty) = tcSplitAppTy a_arg_ty
Richard Eisenberg's avatar
Richard Eisenberg committed
372
    core_arrow <- dsLExprNoLP arrow
373
    core_arg   <- dsLExpr arg
374 375
    stack_id   <- newSysLocalDs stack_ty
    core_make_arg <- matchEnvStack env_ids stack_id core_arg
376
    return (do_premap ids
377
              (envStackType env_ids stack_ty)
378 379 380 381
              arg_ty
              res_ty
              core_make_arg
              core_arrow,
David Feuer's avatar
David Feuer committed
382
            exprFreeIdsDSet core_arg `udfmIntersectUFM` (getUniqSet local_vars))
383

384 385 386 387
-- D, xs |- fun :: a t1 t2
-- D, xs |- arg :: t1
-- ------------------------------
-- D; xs |-a fun -<< arg : stk --> t2
ross's avatar
ross committed
388
--
389
--              ---> premap (\ ((xs), _stk) -> (fun, arg)) app
390

391
dsCmd ids local_vars stack_ty res_ty
392
        (HsCmdArrApp arrow_ty arrow arg HsHigherOrderApp _)
393
        env_ids = do
394 395
    let
        (a_arg_ty, _res_ty') = tcSplitAppTy arrow_ty
ross's avatar
ross committed
396
        (_a_ty, arg_ty) = tcSplitAppTy a_arg_ty
397

398 399
    core_arrow <- dsLExpr arrow
    core_arg   <- dsLExpr arg
400 401 402 403
    stack_id   <- newSysLocalDs stack_ty
    core_make_pair <- matchEnvStack env_ids stack_id
          (mkCorePairExpr core_arrow core_arg)

404
    return (do_premap ids
405
              (envStackType env_ids stack_ty)
406 407 408 409
              (mkCorePairTy arrow_ty arg_ty)
              res_ty
              core_make_pair
              (do_app ids arg_ty res_ty),
niteria's avatar
niteria committed
410
            (exprsFreeIdsDSet [core_arrow, core_arg])
David Feuer's avatar
David Feuer committed
411
              `udfmIntersectUFM` getUniqSet local_vars)
412

413 414 415 416
-- D; ys |-a cmd : (t,stk) --> t'
-- D, xs |-  exp :: t
-- ------------------------
-- D; xs |-a cmd exp : stk --> t'
ross's avatar
ross committed
417
--
418
--              ---> premap (\ ((xs),stk) -> ((ys),(e,stk))) cmd
ross's avatar
ross committed
419

420
dsCmd ids local_vars stack_ty res_ty (HsCmdApp _ cmd arg) env_ids = do
421
    core_arg <- dsLExpr arg
ross's avatar
ross committed
422
    let
423
        arg_ty = exprType core_arg
424
        stack_ty' = mkCorePairTy arg_ty stack_ty
425
    (core_cmd, free_vars, env_ids')
426 427
             <- dsfixCmd ids local_vars stack_ty' res_ty cmd
    stack_id <- newSysLocalDs stack_ty
Richard Eisenberg's avatar
Richard Eisenberg committed
428
    arg_id <- newSysLocalDsNoLP arg_ty
ross's avatar
ross committed
429 430
    -- push the argument expression onto the stack
    let
431
        stack' = mkCorePairExpr (Var arg_id) (Var stack_id)
432
        core_body = bindNonRec arg_id core_arg
433
                        (mkCorePairExpr (mkBigCoreVarTup env_ids') stack')
434

ross's avatar
ross committed
435
    -- match the environment and stack against the input
436
    core_map <- matchEnvStack env_ids stack_id core_body
437
    return (do_premap ids
438 439
                      (envStackType env_ids stack_ty)
                      (envStackType env_ids' stack_ty')
440 441 442
                      res_ty
                      core_map
                      core_cmd,
niteria's avatar
niteria committed
443
            free_vars `unionDVarSet`
David Feuer's avatar
David Feuer committed
444
              (exprFreeIdsDSet core_arg `udfmIntersectUFM` getUniqSet local_vars))
ross's avatar
ross committed
445

446 447 448
-- D; ys |-a cmd : stk t'
-- -----------------------------------------------
-- D; xs |-a \ p1 ... pk -> cmd : (t1,...(tk,stk)...) t'
449
--
450
--              ---> premap (\ ((xs), (p1, ... (pk,stk)...)) -> ((ys),stk)) cmd
451

452
dsCmd ids local_vars stack_ty res_ty
453
        (HsCmdLam _ (MG { mg_alts = L _ [L _ (Match { m_pats  = pats
454
                                                  , m_grhss = GRHSs [L _ (GRHS [] body)] _ })] }))
455
        env_ids = do
456
    let pat_vars = mkVarSet (collectPatsBinders pats)
457
    let
458
        local_vars' = pat_vars `unionVarSet` local_vars
459
        (pat_tys, stack_ty') = splitTypeAt (length pats) stack_ty
460
    (core_body, free_vars, env_ids') <- dsfixCmd ids local_vars' stack_ty' res_ty body
Richard Eisenberg's avatar
Richard Eisenberg committed
461
    param_ids <- mapM newSysLocalDsNoLP pat_tys
462
    stack_id' <- newSysLocalDs stack_ty'
463 464 465 466 467

    -- the expression is built from the inside out, so the actions
    -- are presented in reverse order

    let
468
        -- build a new environment, plus what's left of the stack
469 470 471
        core_expr = buildEnvStack env_ids' stack_id'
        in_ty = envStackType env_ids stack_ty
        in_ty' = envStackType env_ids' stack_ty'
472

473
    fail_expr <- mkFailExpr LambdaExpr in_ty'
474 475 476 477
    -- match the patterns against the parameters
    match_code <- matchSimplys (map Var param_ids) LambdaExpr pats core_expr fail_expr
    -- match the parameters against the top of the old stack
    (stack_id, param_code) <- matchVarStack param_ids stack_id' match_code
478
    -- match the old environment and stack against the input
479
    select_code <- matchEnvStack env_ids stack_id param_code
480
    return (do_premap ids in_ty in_ty' res_ty select_code core_body,
David Feuer's avatar
David Feuer committed
481
            free_vars `udfmMinusUFM` getUniqSet pat_vars)
482

483
dsCmd ids local_vars stack_ty res_ty (HsCmdPar _ cmd) env_ids
484
  = dsLCmd ids local_vars stack_ty res_ty cmd env_ids
485

486 487 488 489 490
-- D, xs |- e :: Bool
-- D; xs1 |-a c1 : stk --> t
-- D; xs2 |-a c2 : stk --> t
-- ----------------------------------------
-- D; xs |-a if e then c1 else c2 : stk --> t
ross's avatar
ross committed
491
--
492 493 494
--              ---> premap (\ ((xs),stk) ->
--                       if e then Left ((xs1),stk) else Right ((xs2),stk))
--                     (c1 ||| c2)
ross's avatar
ross committed
495

496
dsCmd ids local_vars stack_ty res_ty (HsCmdIf _ mb_fun cond then_cmd else_cmd)
497
        env_ids = do
498
    core_cond <- dsLExpr cond
499 500 501
    (core_then, fvs_then, then_ids) <- dsfixCmd ids local_vars stack_ty res_ty then_cmd
    (core_else, fvs_else, else_ids) <- dsfixCmd ids local_vars stack_ty res_ty else_cmd
    stack_id   <- newSysLocalDs stack_ty
502 503 504
    either_con <- dsLookupTyCon eitherTyConName
    left_con   <- dsLookupDataCon leftDataConName
    right_con  <- dsLookupDataCon rightDataConName
505

506 507
    let mk_left_expr ty1 ty2 e = mkCoreConApps left_con   [Type ty1, Type ty2, e]
        mk_right_expr ty1 ty2 e = mkCoreConApps right_con [Type ty1, Type ty2, e]
508

509 510 511
        in_ty = envStackType env_ids stack_ty
        then_ty = envStackType then_ids stack_ty
        else_ty = envStackType else_ids stack_ty
512
        sum_ty = mkTyConApp either_con [then_ty, else_ty]
David Feuer's avatar
David Feuer committed
513
        fvs_cond = exprFreeIdsDSet core_cond `udfmIntersectUFM` getUniqSet local_vars
514

515 516
        core_left  = mk_left_expr  then_ty else_ty (buildEnvStack then_ids stack_id)
        core_right = mk_right_expr then_ty else_ty (buildEnvStack else_ids stack_id)
517

518
    core_if <- case mb_fun of
519 520
       Just fun -> do { fun_apps <- dsSyntaxExpr fun [core_cond, core_left, core_right]
                      ; matchEnvStack env_ids stack_id fun_apps }
521
       Nothing  -> matchEnvStack env_ids stack_id $
522 523
                   mkIfThenElse core_cond core_left core_right

524
    return (do_premap ids in_ty sum_ty res_ty
525 526
                core_if
                (do_choice ids then_ty else_ty res_ty core_then core_else),
niteria's avatar
niteria committed
527
        fvs_cond `unionDVarSet` fvs_then `unionDVarSet` fvs_else)
ross's avatar
ross committed
528

Austin Seipp's avatar
Austin Seipp committed
529
{-
ross's avatar
ross committed
530 531 532
Case commands are treated in much the same way as if commands
(see above) except that there are more alternatives.  For example

533
        case e of { p1 -> c1; p2 -> c2; p3 -> c3 }
ross's avatar
ross committed
534 535 536

is translated to

537 538 539 540 541
        premap (\ ((xs)*ts) -> case e of
                p1 -> (Left (Left (xs1)*ts))
                p2 -> Left ((Right (xs2)*ts))
                p3 -> Right ((xs3)*ts))
        ((c1 ||| c2) ||| c3)
ross's avatar
ross committed
542 543 544 545

The idea is to extract the commands from the case, build a balanced tree
of choices, and replace the commands with expressions that build tagged
tuples, obtaining a case expression that can be desugared normally.
546
To build all this, we use triples describing segments of the list of
ross's avatar
ross committed
547
case bodies, containing the following fields:
548
 * a list of expressions of the form (Left|Right)* ((xs)*ts), to be put
ross's avatar
ross committed
549
   into the case replacing the commands
550
 * a sum type that is the common type of these expressions, and also the
ross's avatar
ross committed
551
   input type of the arrow
552
 * a CoreExpr for an arrow built by combining the translated command
ross's avatar
ross committed
553
   bodies with |||.
Austin Seipp's avatar
Austin Seipp committed
554
-}
ross's avatar
ross committed
555

556
dsCmd ids local_vars stack_ty res_ty
557 558
      (HsCmdCase _ exp (MG { mg_alts = L l matches, mg_arg_tys = arg_tys
                           , mg_origin = origin }))
559
      env_ids = do
560
    stack_id <- newSysLocalDs stack_ty
561 562 563 564 565 566

    -- Extract and desugar the leaf commands in the case, building tuple
    -- expressions that will (after tagging) replace these leaves

    let
        leaves = concatMap leavesMatch matches
567
        make_branch (leaf, bound_vars) = do
568
            (core_leaf, _fvs, leaf_ids) <-
569 570 571
                  dsfixCmd ids (bound_vars `unionVarSet` local_vars) stack_ty res_ty leaf
            return ([mkHsEnvStackExpr leaf_ids stack_id],
                    envStackType leaf_ids stack_ty,
572
                    core_leaf)
573

574 575 576 577
    branches <- mapM make_branch leaves
    either_con <- dsLookupTyCon eitherTyConName
    left_con <- dsLookupDataCon leftDataConName
    right_con <- dsLookupDataCon rightDataConName
578
    let
579 580 581 582 583 584
        left_id  = HsConLikeOut noExt (RealDataCon left_con)
        right_id = HsConLikeOut noExt (RealDataCon right_con)
        left_expr  ty1 ty2 e = noLoc $ HsApp noExt
                           (noLoc $ mkHsWrap (mkWpTyApps [ty1, ty2]) left_id ) e
        right_expr ty1 ty2 e = noLoc $ HsApp noExt
                           (noLoc $ mkHsWrap (mkWpTyApps [ty1, ty2]) right_id) e
585

586 587
        -- Prefix each tuple with a distinct series of Left's and Right's,
        -- in a balanced way, keeping track of the types.
588

589 590 591
        merge_branches (builds1, in_ty1, core_exp1)
                       (builds2, in_ty2, core_exp2)
          = (map (left_expr in_ty1 in_ty2) builds1 ++
592 593 594
                map (right_expr in_ty1 in_ty2) builds2,
             mkTyConApp either_con [in_ty1, in_ty2],
             do_choice ids in_ty1 in_ty2 res_ty core_exp1 core_exp2)
595
        (leaves', sum_ty, core_choices) = foldb merge_branches branches
596 597 598 599 600

        -- Replace the commands in the case with these tagged tuples,
        -- yielding a HsExpr Id we can feed to dsExpr.

        (_, matches') = mapAccumL (replaceLeavesMatch res_ty) leaves' matches
601
        in_ty = envStackType env_ids stack_ty
602

603 604 605 606
    core_body <- dsExpr (HsCase noExt exp
                         (MG { mg_alts = L l matches'
                             , mg_arg_tys = arg_tys
                             , mg_res_ty = sum_ty, mg_origin = origin }))
607 608
        -- Note that we replace the HsCase result type by sum_ty,
        -- which is the type of matches'
609

610
    core_matches <- matchEnvStack env_ids stack_id core_body
611
    return (do_premap ids in_ty sum_ty res_ty core_matches core_choices,
David Feuer's avatar
David Feuer committed
612
            exprFreeIdsDSet core_body `udfmIntersectUFM` getUniqSet local_vars)
613

614 615 616
-- D; ys |-a cmd : stk --> t
-- ----------------------------------
-- D; xs |-a let binds in cmd : stk --> t
617
--
618
--              ---> premap (\ ((xs),stk) -> let binds in ((ys),stk)) c
619

620 621
dsCmd ids local_vars stack_ty res_ty (HsCmdLet _ lbinds@(L _ binds) body)
                                                                    env_ids = do
622
    let
623
        defined_vars = mkVarSet (collectLocalBinders binds)
624
        local_vars' = defined_vars `unionVarSet` local_vars
625

626 627
    (core_body, _free_vars, env_ids') <- dsfixCmd ids local_vars' stack_ty res_ty body
    stack_id <- newSysLocalDs stack_ty
628
    -- build a new environment, plus the stack, using the let bindings
Richard Eisenberg's avatar
Richard Eisenberg committed
629
    core_binds <- dsLocalBinds lbinds (buildEnvStack env_ids' stack_id)
630
    -- match the old environment and stack against the input
631
    core_map <- matchEnvStack env_ids stack_id core_binds
632
    return (do_premap ids
633 634
                        (envStackType env_ids stack_ty)
                        (envStackType env_ids' stack_ty)
635 636 637
                        res_ty
                        core_map
                        core_body,
David Feuer's avatar
David Feuer committed
638
        exprFreeIdsDSet core_binds `udfmIntersectUFM` getUniqSet local_vars)
639

640 641 642 643
-- D; xs |-a ss : t
-- ----------------------------------
-- D; xs |-a do { ss } : () --> t
--
644
--              ---> premap (\ (env,stk) -> env) c
645

646 647
dsCmd ids local_vars stack_ty res_ty do_block@(HsCmdDo stmts_ty (L loc stmts))
                                                                   env_ids = do
Richard Eisenberg's avatar
Richard Eisenberg committed
648 649 650
    putSrcSpanDs loc $
      dsNoLevPoly stmts_ty
        (text "In the do-command:" <+> ppr do_block)
651 652 653 654
    (core_stmts, env_ids') <- dsCmdDo ids local_vars res_ty stmts env_ids
    let env_ty = mkBigCoreVarTupTy env_ids
    core_fst <- mkFstExpr env_ty stack_ty
    return (do_premap ids
655 656 657 658 659 660
                (mkCorePairTy env_ty stack_ty)
                env_ty
                res_ty
                core_fst
                core_stmts,
        env_ids')
661 662 663 664

-- D |- e :: forall e. a1 (e,stk1) t1 -> ... an (e,stkn) tn -> a (e,stk) t
-- D; xs |-a ci :: stki --> ti
-- -----------------------------------
665
-- D; xs |-a (|e c1 ... cn|) :: stk --> t       ---> e [t_xs] c1 ... cn
666

667
dsCmd _ local_vars _stack_ty _res_ty (HsCmdArrForm _ op _ _ args) env_ids = do
668 669 670 671
    let env_ty = mkBigCoreVarTupTy env_ids
    core_op <- dsLExpr op
    (core_args, fv_sets) <- mapAndUnzipM (dsTrimCmdArg local_vars env_ids) args
    return (mkApps (App core_op (Type env_ty)) core_args,
niteria's avatar
niteria committed
672
            unionDVarSets fv_sets)
673

674
dsCmd ids local_vars stack_ty res_ty (HsCmdWrap _ wrap cmd) env_ids = do
675
    (core_cmd, env_ids') <- dsCmd ids local_vars stack_ty res_ty cmd env_ids
Simon Peyton Jones's avatar
Simon Peyton Jones committed
676 677
    core_wrap <- dsHsWrapper wrap
    return (core_wrap core_cmd, env_ids')
678

Ian Lynagh's avatar
Ian Lynagh committed
679 680
dsCmd _ _ _ _ _ c = pprPanic "dsCmd" (ppr c)

681
-- D; ys |-a c : stk --> t      (ys <= xs)
682
-- ---------------------
683
-- D; xs |-a c : stk --> t      ---> premap (\ ((xs),stk) -> ((ys),stk)) c
684 685

dsTrimCmdArg
686
        :: IdSet                -- set of local vars available to this command
687 688
        -> [Id]           -- list of vars in the input to this command
        -> LHsCmdTop GhcTc       -- command argument to desugar
689
        -> DsM (CoreExpr,       -- desugared expression
niteria's avatar
niteria committed
690
                DIdSet)         -- subset of local vars that occur free
691 692
dsTrimCmdArg local_vars env_ids
                       (L _ (HsCmdTop (CmdTopTc stack_ty cmd_ty ids) cmd )) = do
693
    (meth_binds, meth_ids) <- mkCmdEnv ids
694 695 696
    (core_cmd, free_vars, env_ids') <- dsfixCmd meth_ids local_vars stack_ty cmd_ty cmd
    stack_id <- newSysLocalDs stack_ty
    trim_code <- matchEnvStack env_ids stack_id (buildEnvStack env_ids' stack_id)
697
    let
698 699
        in_ty = envStackType env_ids stack_ty
        in_ty' = envStackType env_ids' stack_ty
700
        arg_code = if env_ids' == env_ids then core_cmd else
701
                do_premap meth_ids in_ty in_ty' cmd_ty trim_code core_cmd
702
    return (mkLets meth_binds arg_code, free_vars)
703
dsTrimCmdArg _ _ (L _ XCmdTop{}) = panic "dsTrimCmdArg"
704

705 706
-- Given D; xs |-a c : stk --> t, builds c with xs fed back.
-- Typically needs to be prefixed with arr (\(p, stk) -> ((xs),stk))
707 708

dsfixCmd
709 710 711 712
        :: DsCmdEnv             -- arrow combinators
        -> IdSet                -- set of local vars available to this command
        -> Type                 -- type of the stack (right-nested tuple)
        -> Type                 -- return type of the command
713
        -> LHsCmd GhcTc         -- command to desugar
714
        -> DsM (CoreExpr,       -- desugared expression
niteria's avatar
niteria committed
715
                DIdSet,         -- subset of local vars that occur free
716
                [Id])           -- the same local vars as a list, fed back
717
dsfixCmd ids local_vars stk_ty cmd_ty cmd
Richard Eisenberg's avatar
Richard Eisenberg committed
718 719 720
  = do { putSrcSpanDs (getLoc cmd) $ dsNoLevPoly cmd_ty
           (text "When desugaring the command:" <+> ppr cmd)
       ; trimInput (dsLCmd ids local_vars stk_ty cmd_ty cmd) }
721 722 723 724 725

-- Feed back the list of local variables actually used a command,
-- for use as the input tuple of the generated arrow.

trimInput
niteria's avatar
niteria committed
726
        :: ([Id] -> DsM (CoreExpr, DIdSet))
727
        -> DsM (CoreExpr,       -- desugared expression
niteria's avatar
niteria committed
728
                DIdSet,         -- subset of local vars that occur free
729 730 731
                [Id])           -- same local vars as a list, fed back to
                                -- the inner function to form the tuple of
                                -- inputs to the arrow.
732 733 734
trimInput build_arrow
  = fixDs (\ ~(_,_,env_ids) -> do
        (core_cmd, free_vars) <- build_arrow env_ids
niteria's avatar
niteria committed
735
        return (core_cmd, free_vars, dVarSetElems free_vars))
736

Austin Seipp's avatar
Austin Seipp committed
737
{-
738 739
Translation of command judgements of the form

740
        D |-a do { ss } : t
Austin Seipp's avatar
Austin Seipp committed
741
-}
742

743 744 745
dsCmdDo :: DsCmdEnv             -- arrow combinators
        -> IdSet                -- set of local vars available to this statement
        -> Type                 -- return type of the statement
746
        -> [CmdLStmt GhcTc]     -- statements to desugar
747 748 749 750
        -> [Id]                 -- list of vars in the input to this statement
                                -- This is typically fed back,
                                -- so don't pull on it too early
        -> DsM (CoreExpr,       -- desugared expression
niteria's avatar
niteria committed
751
                DIdSet)         -- subset of local vars that occur free
752

753
dsCmdDo _ _ _ [] _ = panic "dsCmdDo"
754

755 756 757 758
-- D; xs |-a c : () --> t
-- --------------------------
-- D; xs |-a do { c } : t
--
759
--              ---> premap (\ (xs) -> ((xs), ())) c
760

Richard Eisenberg's avatar
Richard Eisenberg committed
761 762 763
dsCmdDo ids local_vars res_ty [L loc (LastStmt body _ _)] env_ids = do
    putSrcSpanDs loc $ dsNoLevPoly res_ty
                         (text "In the command:" <+> ppr body)
764 765 766 767 768 769
    (core_body, env_ids') <- dsLCmd ids local_vars unitTy res_ty body env_ids
    let env_ty = mkBigCoreVarTupTy env_ids
    env_var <- newSysLocalDs env_ty
    let core_map = Lam env_var (mkCorePairExpr (Var env_var) mkCoreUnitExpr)
    return (do_premap ids
                        env_ty
770
                        (mkCorePairTy env_ty unitTy)
771 772 773
                        res_ty
                        core_map
                        core_body,
774
        env_ids')
775

776
dsCmdDo ids local_vars res_ty (stmt:stmts) env_ids = do
777 778
    let bound_vars  = mkVarSet (collectLStmtBinders stmt)
    let local_vars' = bound_vars `unionVarSet` local_vars
779 780
    (core_stmts, _, env_ids') <- trimInput (dsCmdDo ids local_vars' res_ty stmts)
    (core_stmt, fv_stmt) <- dsCmdLStmt ids local_vars env_ids' stmt env_ids
781 782 783 784 785 786 787
    return (do_compose ids
                (mkBigCoreVarTupTy env_ids)
                (mkBigCoreVarTupTy env_ids')
                res_ty
                core_stmt
                core_stmts,
              fv_stmt)
788

Austin Seipp's avatar
Austin Seipp committed
789
{-
ross's avatar
ross committed
790 791 792
A statement maps one local environment to another, and is represented
as an arrow from one tuple type to another.  A statement sequence is
translated to a composition of such arrows.
Austin Seipp's avatar
Austin Seipp committed
793 794
-}

795
dsCmdLStmt :: DsCmdEnv -> IdSet -> [Id] -> CmdLStmt GhcTc -> [Id]
niteria's avatar
niteria committed
796
           -> DsM (CoreExpr, DIdSet)
797 798
dsCmdLStmt ids local_vars out_ids cmd env_ids
  = dsCmdStmt ids local_vars out_ids (unLoc cmd) env_ids