DsArrows.hs 48.3 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 #-}
11
{-# LANGUAGE ViewPatterns #-}
Ian Lynagh's avatar
Ian Lynagh committed
12

13 14 15 16
module DsArrows ( dsProcExpr ) where

#include "HsVersions.h"

17 18
import GhcPrelude

Simon Marlow's avatar
Simon Marlow committed
19 20
import Match
import DsUtils
21 22
import DsMonad

23 24 25
import HsSyn    hiding (collectPatBinders, collectPatsBinders,
                        collectLStmtsBinders, collectLStmtBinders,
                        collectStmtBinders )
Simon Marlow's avatar
Simon Marlow committed
26
import TcHsSyn
Simon Marlow's avatar
Simon Marlow committed
27
import qualified HsUtils
28 29 30 31 32 33

-- 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.

34 35
import {-# SOURCE #-} DsExpr ( dsExpr, dsLExpr, dsLExprNoLP, dsLocalBinds,
                               dsSyntaxExpr )
36

Simon Marlow's avatar
Simon Marlow committed
37
import TcType
Richard Eisenberg's avatar
Richard Eisenberg committed
38
import Type ( splitPiTy )
39
import TcEvidence
40
import CoreSyn
Simon Marlow's avatar
Simon Marlow committed
41 42
import CoreFVs
import CoreUtils
43
import MkCore
44
import DsBinds (dsHsWrapper)
45

Simon Marlow's avatar
Simon Marlow committed
46
import Name
47
import Id
Richard Eisenberg's avatar
Richard Eisenberg committed
48
import ConLike
Simon Marlow's avatar
Simon Marlow committed
49 50 51
import TysWiredIn
import BasicTypes
import PrelNames
Ian Lynagh's avatar
Ian Lynagh committed
52
import Outputable
Simon Marlow's avatar
Simon Marlow committed
53 54
import VarSet
import SrcLoc
Richard Eisenberg's avatar
Richard Eisenberg committed
55
import ListSetOps( assocMaybe )
56
import Data.List
niteria's avatar
niteria committed
57
import Util
Sebastian Graf's avatar
Sebastian Graf committed
58
import UniqDSet
59 60

data DsCmdEnv = DsCmdEnv {
61
        arr_id, compose_id, first_id, app_id, choice_id, loop_id :: CoreExpr
62 63
    }

64
mkCmdEnv :: CmdSyntaxTable GhcTc -> DsM ([CoreBind], DsCmdEnv)
65 66 67
-- See Note [CmdSyntaxTable] in HsExpr
mkCmdEnv tc_meths
  = do { (meth_binds, prs) <- mapAndUnzipM mk_bind tc_meths
Richard Eisenberg's avatar
Richard Eisenberg committed
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 96 97

       -- 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

98
       ; return (meth_binds, DsCmdEnv {
Richard Eisenberg's avatar
Richard Eisenberg committed
99 100 101 102 103 104
               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)
105 106 107 108
             }) }
  where
    mk_bind (std_name, expr)
      = do { rhs <- dsExpr expr
109 110
           ; id <- newSysLocalDs (exprType rhs)
           -- no check needed; these are functions
111
           ; return (NonRec id rhs, (std_name, id)) }
112

Richard Eisenberg's avatar
Richard Eisenberg committed
113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129
    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))

130 131 132 133 134 135 136

-- 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 ->
137
                CoreExpr -> CoreExpr -> CoreExpr
138 139 140 141 142 143 144 145 146 147 148 149 150 151 152
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 ->
153
                CoreExpr -> CoreExpr -> CoreExpr
154 155 156 157 158 159 160 161 162
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]

163 164 165
-- 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 ->
166
                CoreExpr -> CoreExpr -> CoreExpr
167 168
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
169

170
mkFailExpr :: HsMatchContext Id -> Type -> DsM CoreExpr
171 172 173
mkFailExpr ctxt ty
  = mkErrorAppDs pAT_ERROR_ID ty (matchContextErrString ctxt)

174 175 176 177 178 179 180 181 182
-- 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)))

183 184
-- construct CoreExpr for \ (a :: a_ty, b :: b_ty) -> b
mkSndExpr :: Type -> Type -> DsM CoreExpr
185 186 187 188 189 190
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)))
191

Austin Seipp's avatar
Austin Seipp committed
192
{-
193 194
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
195
-}
196 197

-- coreCaseTuple [u1..] v [x1..xn] body
198
--      = case v of v { (x1, .., xn) -> body }
199 200 201
-- But the matching may be nested if the tuple is very big

coreCaseTuple :: UniqSupply -> Id -> [Id] -> CoreExpr -> CoreExpr
ross's avatar
ross committed
202 203
coreCaseTuple uniqs scrut_var vars body
  = mkTupleCase uniqs vars body scrut_var (Var scrut_var)
204

ross's avatar
ross committed
205 206
coreCasePair :: Id -> Id -> Id -> CoreExpr -> CoreExpr
coreCasePair scrut_var var1 var2 body
207
  = Case (Var scrut_var) scrut_var (exprType body)
208
         [(DataAlt (tupleDataCon Boxed 2), [var1, var2], body)]
209 210

mkCorePairTy :: Type -> Type -> Type
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
211
mkCorePairTy t1 t2 = mkBoxedTupleTy [t1, t2]
212 213 214

mkCorePairExpr :: CoreExpr -> CoreExpr -> CoreExpr
mkCorePairExpr e1 e2 = mkCoreTup [e1, e2]
215 216 217

mkCoreUnitExpr :: CoreExpr
mkCoreUnitExpr = mkCoreTup []
218

Austin Seipp's avatar
Austin Seipp committed
219
{-
220
The input is divided into a local environment, which is a flat tuple
221 222
(unless it's too big), and a stack, which is a right-nested pair.
In general, the input has the form
223

224
        ((x1,...,xn), (s1,...(sk,())...))
225 226 227

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
228
-}
229

230 231 232 233 234 235 236 237 238 239
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)
240 241

----------------------------------------------
242
--              buildEnvStack
243
--
244
--      ((x1,...,xn),stk)
245

246 247 248
buildEnvStack :: [Id] -> Id -> CoreExpr
buildEnvStack env_ids stack_id
  = mkCorePairExpr (mkBigCoreVarTup env_ids) (Var stack_id)
249 250

----------------------------------------------
251
--              matchEnvStack
252
--
253 254 255 256 257 258 259 260 261 262 263
--      \ ((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
264
matchEnvStack env_ids stack_id body = do
265 266
    uniqs <- newUniqueSupply
    tup_var <- newSysLocalDs (mkBigCoreVarTupTy env_ids)
267 268 269
    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))
270

271
----------------------------------------------
272
--              matchEnv
273
--
274 275 276 277 278 279 280 281 282
--      \ (x1,...,xn) -> body
--      =>
--      \ tup ->
--      case tup of (x1,...,xn) ->
--      body

matchEnv :: [Id]        -- x1..xn
         -> CoreExpr    -- e
         -> DsM CoreExpr
283 284 285 286
matchEnv env_ids body = do
    uniqs <- newUniqueSupply
    tup_id <- newSysLocalDs (mkBigCoreVarTupTy env_ids)
    return (Lam tup_id (coreCaseTuple uniqs tup_id env_ids body))
287 288

----------------------------------------------
289
--              matchVarStack
290
--
291 292 293 294 295
--      case (x1, ...(xn, s)...) -> e
--      =>
--      case z0 of (x1,z1) ->
--      case zn-1 of (xn,s) ->
--      e
296 297 298 299 300 301
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)
302

303
mkHsEnvStackExpr :: [Id] -> Id -> LHsExpr GhcTc
304 305
mkHsEnvStackExpr env_ids stack_id
  = mkLHsTupleExpr [mkLHsVarTuple env_ids, nlHsVar stack_id]
306

Austin Seipp's avatar
Austin Seipp committed
307
-- Translation of arrow abstraction
308

309
-- D; xs |-a c : () --> t'      ---> c'
310
-- --------------------------
311
-- D |- proc p -> c :: a t t'   ---> premap (\ p -> ((xs),())) c'
312
--
313
--              where (xs) is the tuple of variables bound by p
314 315

dsProcExpr
316 317
        :: LPat GhcTc
        -> LHsCmdTop GhcTc
318
        -> DsM CoreExpr
319
dsProcExpr pat (dL->L _ (HsCmdTop (CmdTopTc _unitTy cmd_ty ids) cmd)) = do
320
    (meth_binds, meth_ids) <- mkCmdEnv ids
321
    let locals = mkVarSet (collectPatBinders pat)
322 323
    (core_cmd, _free_vars, env_ids)
       <- dsfixCmd meth_ids locals unitTy cmd_ty cmd
324
    let env_ty = mkBigCoreVarTupTy env_ids
325 326 327
    let env_stk_ty = mkCorePairTy env_ty unitTy
    let env_stk_expr = mkCorePairExpr (mkBigCoreVarTup env_ids) mkCoreUnitExpr
    fail_expr <- mkFailExpr ProcExpr env_stk_ty
328
    var <- selectSimpleMatchVarL pat
329
    match_code <- matchSimply (Var var) ProcExpr pat env_stk_expr fail_expr
330
    let pat_ty = hsLPatType pat
331
    let proc_code = do_premap meth_ids pat_ty env_stk_ty cmd_ty
332 333
                    (Lam var match_code)
                    core_cmd
334
    return (mkLets meth_binds proc_code)
335
dsProcExpr _ _ = panic "dsProcExpr"
336

Austin Seipp's avatar
Austin Seipp committed
337
{-
338 339
Translation of a command judgement of the form

340
        D; xs |-a c : stk --> t
341 342

to an expression e such that
343

344
        D |- e :: a (xs, stk) t
Austin Seipp's avatar
Austin Seipp committed
345
-}
346

347
dsLCmd :: DsCmdEnv -> IdSet -> Type -> Type -> LHsCmd GhcTc -> [Id]
niteria's avatar
niteria committed
348
       -> DsM (CoreExpr, DIdSet)
349 350
dsLCmd ids local_vars stk_ty res_ty cmd env_ids
  = dsCmd ids local_vars stk_ty res_ty (unLoc cmd) env_ids
351

352 353 354 355
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
356 357
        -> HsCmd GhcTc           -- command to desugar
        -> [Id]           -- list of vars in the input to this command
358 359 360
                                -- This is typically fed back,
                                -- so don't pull on it too early
        -> DsM (CoreExpr,       -- desugared expression
niteria's avatar
niteria committed
361
                DIdSet)         -- subset of local vars that occur free
362

363 364 365 366
-- D |- fun :: a t1 t2
-- D, xs |- arg :: t1
-- -----------------------------
-- D; xs |-a fun -< arg : stk --> t2
ross's avatar
ross committed
367
--
368
--              ---> premap (\ ((xs), _stk) -> arg) fun
369

370
dsCmd ids local_vars stack_ty res_ty
371
        (HsCmdArrApp arrow_ty arrow arg HsFirstOrderApp _)
372
        env_ids = do
373 374
    let
        (a_arg_ty, _res_ty') = tcSplitAppTy arrow_ty
ross's avatar
ross committed
375
        (_a_ty, arg_ty) = tcSplitAppTy a_arg_ty
Richard Eisenberg's avatar
Richard Eisenberg committed
376
    core_arrow <- dsLExprNoLP arrow
377
    core_arg   <- dsLExpr arg
378 379
    stack_id   <- newSysLocalDs stack_ty
    core_make_arg <- matchEnvStack env_ids stack_id core_arg
380
    return (do_premap ids
381
              (envStackType env_ids stack_ty)
382 383 384 385
              arg_ty
              res_ty
              core_make_arg
              core_arrow,
Sebastian Graf's avatar
Sebastian Graf committed
386
            exprFreeIdsDSet core_arg `uniqDSetIntersectUniqSet` local_vars)
387

388 389 390 391
-- D, xs |- fun :: a t1 t2
-- D, xs |- arg :: t1
-- ------------------------------
-- D; xs |-a fun -<< arg : stk --> t2
ross's avatar
ross committed
392
--
393
--              ---> premap (\ ((xs), _stk) -> (fun, arg)) app
394

395
dsCmd ids local_vars stack_ty res_ty
396
        (HsCmdArrApp arrow_ty arrow arg HsHigherOrderApp _)
397
        env_ids = do
398 399
    let
        (a_arg_ty, _res_ty') = tcSplitAppTy arrow_ty
ross's avatar
ross committed
400
        (_a_ty, arg_ty) = tcSplitAppTy a_arg_ty
401

402 403
    core_arrow <- dsLExpr arrow
    core_arg   <- dsLExpr arg
404 405 406 407
    stack_id   <- newSysLocalDs stack_ty
    core_make_pair <- matchEnvStack env_ids stack_id
          (mkCorePairExpr core_arrow core_arg)

408
    return (do_premap ids
409
              (envStackType env_ids stack_ty)
410 411 412 413
              (mkCorePairTy arrow_ty arg_ty)
              res_ty
              core_make_pair
              (do_app ids arg_ty res_ty),
niteria's avatar
niteria committed
414
            (exprsFreeIdsDSet [core_arrow, core_arg])
Sebastian Graf's avatar
Sebastian Graf committed
415
              `uniqDSetIntersectUniqSet` local_vars)
416

417 418 419 420
-- D; ys |-a cmd : (t,stk) --> t'
-- D, xs |-  exp :: t
-- ------------------------
-- D; xs |-a cmd exp : stk --> t'
ross's avatar
ross committed
421
--
422
--              ---> premap (\ ((xs),stk) -> ((ys),(e,stk))) cmd
ross's avatar
ross committed
423

424
dsCmd ids local_vars stack_ty res_ty (HsCmdApp _ cmd arg) env_ids = do
425
    core_arg <- dsLExpr arg
ross's avatar
ross committed
426
    let
427
        arg_ty = exprType core_arg
428
        stack_ty' = mkCorePairTy arg_ty stack_ty
429
    (core_cmd, free_vars, env_ids')
430 431
             <- dsfixCmd ids local_vars stack_ty' res_ty cmd
    stack_id <- newSysLocalDs stack_ty
Richard Eisenberg's avatar
Richard Eisenberg committed
432
    arg_id <- newSysLocalDsNoLP arg_ty
ross's avatar
ross committed
433 434
    -- push the argument expression onto the stack
    let
435
        stack' = mkCorePairExpr (Var arg_id) (Var stack_id)
436
        core_body = bindNonRec arg_id core_arg
437
                        (mkCorePairExpr (mkBigCoreVarTup env_ids') stack')
438

ross's avatar
ross committed
439
    -- match the environment and stack against the input
440
    core_map <- matchEnvStack env_ids stack_id core_body
441
    return (do_premap ids
442 443
                      (envStackType env_ids stack_ty)
                      (envStackType env_ids' stack_ty')
444 445 446
                      res_ty
                      core_map
                      core_cmd,
niteria's avatar
niteria committed
447
            free_vars `unionDVarSet`
Sebastian Graf's avatar
Sebastian Graf committed
448
              (exprFreeIdsDSet core_arg `uniqDSetIntersectUniqSet` local_vars))
ross's avatar
ross committed
449

450 451 452
-- D; ys |-a cmd : stk t'
-- -----------------------------------------------
-- D; xs |-a \ p1 ... pk -> cmd : (t1,...(tk,stk)...) t'
453
--
454
--              ---> premap (\ ((xs), (p1, ... (pk,stk)...)) -> ((ys),stk)) cmd
455

456
dsCmd ids local_vars stack_ty res_ty
457
        (HsCmdLam _ (MG { mg_alts
458 459
          = (dL->L _ [dL->L _ (Match { m_pats  = pats
                       , m_grhss = GRHSs _ [dL->L _ (GRHS _ [] body)] _ })]) }))
460
        env_ids = do
461
    let pat_vars = mkVarSet (collectPatsBinders pats)
462
    let
463
        local_vars' = pat_vars `unionVarSet` local_vars
464
        (pat_tys, stack_ty') = splitTypeAt (length pats) stack_ty
465 466
    (core_body, free_vars, env_ids')
       <- dsfixCmd ids local_vars' stack_ty' res_ty body
Richard Eisenberg's avatar
Richard Eisenberg committed
467
    param_ids <- mapM newSysLocalDsNoLP pat_tys
468
    stack_id' <- newSysLocalDs stack_ty'
469 470 471 472 473

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

    let
474
        -- build a new environment, plus what's left of the stack
475 476 477
        core_expr = buildEnvStack env_ids' stack_id'
        in_ty = envStackType env_ids stack_ty
        in_ty' = envStackType env_ids' stack_ty'
478

479
    fail_expr <- mkFailExpr LambdaExpr in_ty'
480
    -- match the patterns against the parameters
481 482
    match_code <- matchSimplys (map Var param_ids) LambdaExpr pats core_expr
                    fail_expr
483 484
    -- match the parameters against the top of the old stack
    (stack_id, param_code) <- matchVarStack param_ids stack_id' match_code
485
    -- match the old environment and stack against the input
486
    select_code <- matchEnvStack env_ids stack_id param_code
487
    return (do_premap ids in_ty in_ty' res_ty select_code core_body,
Sebastian Graf's avatar
Sebastian Graf committed
488
            free_vars `uniqDSetMinusUniqSet` pat_vars)
489

490
dsCmd ids local_vars stack_ty res_ty (HsCmdPar _ cmd) env_ids
491
  = dsLCmd ids local_vars stack_ty res_ty cmd env_ids
492

493 494 495 496 497
-- 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
498
--
499 500 501
--              ---> premap (\ ((xs),stk) ->
--                       if e then Left ((xs1),stk) else Right ((xs2),stk))
--                     (c1 ||| c2)
ross's avatar
ross committed
502

503
dsCmd ids local_vars stack_ty res_ty (HsCmdIf _ mb_fun cond then_cmd else_cmd)
504
        env_ids = do
505
    core_cond <- dsLExpr cond
506 507 508 509
    (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
510
    stack_id   <- newSysLocalDs stack_ty
511 512 513
    either_con <- dsLookupTyCon eitherTyConName
    left_con   <- dsLookupDataCon leftDataConName
    right_con  <- dsLookupDataCon rightDataConName
514

515 516
    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]
517

518 519 520
        in_ty = envStackType env_ids stack_ty
        then_ty = envStackType then_ids stack_ty
        else_ty = envStackType else_ids stack_ty
521
        sum_ty = mkTyConApp either_con [then_ty, else_ty]
522 523
        fvs_cond = exprFreeIdsDSet core_cond
                   `uniqDSetIntersectUniqSet` local_vars
524

525 526 527 528
        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)
529

530
    core_if <- case mb_fun of
531 532
       Just fun -> do { fun_apps <- dsSyntaxExpr fun
                                      [core_cond, core_left, core_right]
533
                      ; matchEnvStack env_ids stack_id fun_apps }
534
       Nothing  -> matchEnvStack env_ids stack_id $
535 536
                   mkIfThenElse core_cond core_left core_right

537
    return (do_premap ids in_ty sum_ty res_ty
538 539
                core_if
                (do_choice ids then_ty else_ty res_ty core_then core_else),
niteria's avatar
niteria committed
540
        fvs_cond `unionDVarSet` fvs_then `unionDVarSet` fvs_else)
ross's avatar
ross committed
541

Austin Seipp's avatar
Austin Seipp committed
542
{-
ross's avatar
ross committed
543 544 545
Case commands are treated in much the same way as if commands
(see above) except that there are more alternatives.  For example

546
        case e of { p1 -> c1; p2 -> c2; p3 -> c3 }
ross's avatar
ross committed
547 548 549

is translated to

550 551 552 553 554
        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
555 556 557 558

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.
559
To build all this, we use triples describing segments of the list of
ross's avatar
ross committed
560
case bodies, containing the following fields:
561
 * a list of expressions of the form (Left|Right)* ((xs)*ts), to be put
ross's avatar
ross committed
562
   into the case replacing the commands
563
 * a sum type that is the common type of these expressions, and also the
ross's avatar
ross committed
564
   input type of the arrow
565
 * a CoreExpr for an arrow built by combining the translated command
ross's avatar
ross committed
566
   bodies with |||.
Austin Seipp's avatar
Austin Seipp committed
567
-}
ross's avatar
ross committed
568

569
dsCmd ids local_vars stack_ty res_ty
570
      (HsCmdCase _ exp (MG { mg_alts = (dL->L l matches)
571
                           , mg_ext = MatchGroupTc arg_tys _
572
                           , mg_origin = origin }))
573
      env_ids = do
574
    stack_id <- newSysLocalDs stack_ty
575 576 577 578 579 580

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

    let
        leaves = concatMap leavesMatch matches
581
        make_branch (leaf, bound_vars) = do
582 583 584
            (core_leaf, _fvs, leaf_ids)
               <- dsfixCmd ids (bound_vars `unionVarSet` local_vars) stack_ty
                    res_ty leaf
585 586
            return ([mkHsEnvStackExpr leaf_ids stack_id],
                    envStackType leaf_ids stack_ty,
587
                    core_leaf)
588

589 590 591 592
    branches <- mapM make_branch leaves
    either_con <- dsLookupTyCon eitherTyConName
    left_con <- dsLookupDataCon leftDataConName
    right_con <- dsLookupDataCon rightDataConName
593
    let
594 595 596
        left_id  = HsConLikeOut noExtField (RealDataCon left_con)
        right_id = HsConLikeOut noExtField (RealDataCon right_con)
        left_expr  ty1 ty2 e = noLoc $ HsApp noExtField
597
                           (noLoc $ mkHsWrap (mkWpTyApps [ty1, ty2]) left_id ) e
598
        right_expr ty1 ty2 e = noLoc $ HsApp noExtField
599
                           (noLoc $ mkHsWrap (mkWpTyApps [ty1, ty2]) right_id) e
600

601 602
        -- Prefix each tuple with a distinct series of Left's and Right's,
        -- in a balanced way, keeping track of the types.
603

604 605 606
        merge_branches (builds1, in_ty1, core_exp1)
                       (builds2, in_ty2, core_exp2)
          = (map (left_expr in_ty1 in_ty2) builds1 ++
607 608 609
                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)
610
        (leaves', sum_ty, core_choices) = foldb merge_branches branches
611 612 613 614 615

        -- 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
616
        in_ty = envStackType env_ids stack_ty
617

618
    core_body <- dsExpr (HsCase noExtField exp
619
                         (MG { mg_alts = cL l matches'
620 621
                             , mg_ext = MatchGroupTc arg_tys sum_ty
                             , mg_origin = origin }))
622 623
        -- Note that we replace the HsCase result type by sum_ty,
        -- which is the type of matches'
624

625
    core_matches <- matchEnvStack env_ids stack_id core_body
626
    return (do_premap ids in_ty sum_ty res_ty core_matches core_choices,
Sebastian Graf's avatar
Sebastian Graf committed
627
            exprFreeIdsDSet core_body `uniqDSetIntersectUniqSet` local_vars)
628

629 630 631
-- D; ys |-a cmd : stk --> t
-- ----------------------------------
-- D; xs |-a let binds in cmd : stk --> t
632
--
633
--              ---> premap (\ ((xs),stk) -> let binds in ((ys),stk)) c
634

635
dsCmd ids local_vars stack_ty res_ty (HsCmdLet _ lbinds@(dL->L _ binds) body)
636
                                                                    env_ids = do
637
    let
638
        defined_vars = mkVarSet (collectLocalBinders binds)
639
        local_vars' = defined_vars `unionVarSet` local_vars
640

641 642
    (core_body, _free_vars, env_ids')
       <- dsfixCmd ids local_vars' stack_ty res_ty body
643
    stack_id <- newSysLocalDs stack_ty
644
    -- build a new environment, plus the stack, using the let bindings
Richard Eisenberg's avatar
Richard Eisenberg committed
645
    core_binds <- dsLocalBinds lbinds (buildEnvStack env_ids' stack_id)
646
    -- match the old environment and stack against the input
647
    core_map <- matchEnvStack env_ids stack_id core_binds
648
    return (do_premap ids
649 650
                        (envStackType env_ids stack_ty)
                        (envStackType env_ids' stack_ty)
651 652 653
                        res_ty
                        core_map
                        core_body,
Sebastian Graf's avatar
Sebastian Graf committed
654
        exprFreeIdsDSet core_binds `uniqDSetIntersectUniqSet` local_vars)
655

656 657 658 659
-- D; xs |-a ss : t
-- ----------------------------------
-- D; xs |-a do { ss } : () --> t
--
660
--              ---> premap (\ (env,stk) -> env) c
661

662 663
dsCmd ids local_vars stack_ty res_ty do_block@(HsCmdDo stmts_ty
                                               (dL->L loc stmts))
664
                                                                   env_ids = do
Richard Eisenberg's avatar
Richard Eisenberg committed
665 666 667
    putSrcSpanDs loc $
      dsNoLevPoly stmts_ty
        (text "In the do-command:" <+> ppr do_block)
668 669 670 671
    (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
672 673 674 675 676 677
                (mkCorePairTy env_ty stack_ty)
                env_ty
                res_ty
                core_fst
                core_stmts,
        env_ids')
678 679 680 681

-- D |- e :: forall e. a1 (e,stk1) t1 -> ... an (e,stkn) tn -> a (e,stk) t
-- D; xs |-a ci :: stki --> ti
-- -----------------------------------
682
-- D; xs |-a (|e c1 ... cn|) :: stk --> t       ---> e [t_xs] c1 ... cn
683

684
dsCmd _ local_vars _stack_ty _res_ty (HsCmdArrForm _ op _ _ args) env_ids = do
685 686 687 688
    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
689
            unionDVarSets fv_sets)
690

691
dsCmd ids local_vars stack_ty res_ty (HsCmdWrap _ wrap cmd) env_ids = do
692
    (core_cmd, env_ids') <- dsCmd ids local_vars stack_ty res_ty cmd env_ids
Simon Peyton Jones's avatar
Simon Peyton Jones committed
693 694
    core_wrap <- dsHsWrapper wrap
    return (core_wrap core_cmd, env_ids')
695

Ian Lynagh's avatar
Ian Lynagh committed
696 697
dsCmd _ _ _ _ _ c = pprPanic "dsCmd" (ppr c)

698
-- D; ys |-a c : stk --> t      (ys <= xs)
699
-- ---------------------
700
-- D; xs |-a c : stk --> t      ---> premap (\ ((xs),stk) -> ((ys),stk)) c
701 702

dsTrimCmdArg
703
        :: IdSet                -- set of local vars available to this command
704 705
        -> [Id]           -- list of vars in the input to this command
        -> LHsCmdTop GhcTc       -- command argument to desugar
706
        -> DsM (CoreExpr,       -- desugared expression
niteria's avatar
niteria committed
707
                DIdSet)         -- subset of local vars that occur free
708
dsTrimCmdArg local_vars env_ids
709 710
                       (dL->L _ (HsCmdTop
                                 (CmdTopTc stack_ty cmd_ty ids) cmd )) = do
711
    (meth_binds, meth_ids) <- mkCmdEnv ids
712 713
    (core_cmd, free_vars, env_ids')
       <- dsfixCmd meth_ids local_vars stack_ty cmd_ty cmd
714
    stack_id <- newSysLocalDs stack_ty
715 716
    trim_code
      <- matchEnvStack env_ids stack_id (buildEnvStack env_ids' stack_id)
717
    let
718 719
        in_ty = envStackType env_ids stack_ty
        in_ty' = envStackType env_ids' stack_ty
720
        arg_code = if env_ids' == env_ids then core_cmd else
721
                do_premap meth_ids in_ty in_ty' cmd_ty trim_code core_cmd
722
    return (mkLets meth_binds arg_code, free_vars)
723
dsTrimCmdArg _ _ _ = panic "dsTrimCmdArg"
724

725 726
-- Given D; xs |-a c : stk --> t, builds c with xs fed back.
-- Typically needs to be prefixed with arr (\(p, stk) -> ((xs),stk))
727 728

dsfixCmd
729 730 731 732
        :: 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
733
        -> LHsCmd GhcTc         -- command to desugar
734
        -> DsM (CoreExpr,       -- desugared expression
niteria's avatar
niteria committed
735
                DIdSet,         -- subset of local vars that occur free
736
                [Id])           -- the same local vars as a list, fed back
737
dsfixCmd ids local_vars stk_ty cmd_ty cmd
Richard Eisenberg's avatar
Richard Eisenberg committed
738 739 740
  = do { putSrcSpanDs (getLoc cmd) $ dsNoLevPoly cmd_ty
           (text "When desugaring the command:" <+> ppr cmd)
       ; trimInput (dsLCmd ids local_vars stk_ty cmd_ty cmd) }
741 742 743 744 745

-- 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
746
        :: ([Id] -> DsM (CoreExpr, DIdSet))
747
        -> DsM (CoreExpr,       -- desugared expression
niteria's avatar
niteria committed
748
                DIdSet,         -- subset of local vars that occur free
749 750 751
                [Id])           -- same local vars as a list, fed back to
                                -- the inner function to form the tuple of
                                -- inputs to the arrow.
752 753 754
trimInput build_arrow
  = fixDs (\ ~(_,_,env_ids) -> do
        (core_cmd, free_vars) <- build_arrow env_ids
niteria's avatar
niteria committed
755
        return (core_cmd, free_vars, dVarSetElems free_vars))
756

Austin Seipp's avatar
Austin Seipp committed
757
{-
758 759
Translation of command judgements of the form

760
        D |-a do { ss } : t
Austin Seipp's avatar
Austin Seipp committed
761
-}
762

763 764 765
dsCmdDo :: DsCmdEnv             -- arrow combinators
        -> IdSet                -- set of local vars available to this statement
        -> Type                 -- return type of the statement
766
        -> [CmdLStmt GhcTc]     -- statements to desugar
767 768 769 770
        -> [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
771
                DIdSet)         -- subset of local vars that occur free
772

773
dsCmdDo _ _ _ [] _ = panic "dsCmdDo"
774

775 776 777 778
-- D; xs |-a c : () --> t
-- --------------------------
-- D; xs |-a do { c } : t
--
779
--              ---> premap (\ (xs) -> ((xs), ())) c
780

781
dsCmdDo ids local_vars res_ty [dL->L loc (LastStmt _ body _ _)] env_ids = do
Richard Eisenberg's avatar
Richard Eisenberg committed
782 783
    putSrcSpanDs loc $ dsNoLevPoly res_ty
                         (text "In the command:" <+> ppr body)
784 785 786 787 788 789
    (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
790
                        (mkCorePairTy env_ty unitTy)
791