2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcModule]{Typechecking a whole module}
9 mkGlobalContext, getModuleContents, tcRnStmt, tcRnThing, tcRnExpr,
11 tcRnModule, checkOldIface,
12 importSupportingDecls, tcTopSrcDecls,
13 tcRnIface, tcRnExtCore
16 #include "HsVersions.h"
19 import {-# SOURCE #-} TcSplice ( tcSpliceDecls )
20 import DsMeta ( templateHaskellNames )
23 import CmdLineOpts ( DynFlag(..), opt_PprStyle_Debug, dopt )
24 import DriverState ( v_MainModIs, v_MainFunIs )
25 import DriverUtil ( split_longest_prefix )
26 import HsSyn ( HsModule(..), HsBinds(..), MonoBinds(..), HsExpr(..),
27 Stmt(..), Pat(VarPat), HsStmtContext(..), RuleDecl(..),
28 HsGroup(..), SpliceDecl(..),
29 mkSimpleMatch, placeHolderType, toHsType, andMonoBinds,
30 isSrcRule, collectStmtsBinders
32 import RdrHsSyn ( RdrNameHsModule, RdrNameHsDecl, RdrNameStmt, RdrNameHsExpr,
33 emptyGroup, mkGroup, findSplice, addImpDecls, main_RDR_Unqual )
35 import PrelNames ( iNTERACTIVE, ioTyConName, printName,
36 returnIOName, bindIOName, failIOName, thenIOName, runIOName,
37 dollarMainName, itName, mAIN_Name, unsafeCoerceName
39 import MkId ( unsafeCoerceId )
40 import RdrName ( RdrName, getRdrName, mkRdrUnqual,
41 lookupRdrEnv, elemRdrEnv )
43 import RnHsSyn ( RenamedStmt, RenamedTyClDecl,
44 ruleDeclFVs, instDeclFVs, tyClDeclFVs )
45 import TcHsSyn ( TypecheckedHsExpr, TypecheckedRuleDecl,
46 zonkTopDecls, mkHsLet,
47 zonkTopExpr, zonkTopBndrs
50 import TcExpr ( tcInferRho, tcCheckRho )
52 import TcMType ( newTyVarTy, zonkTcType )
53 import TcType ( Type, liftedTypeKind,
54 tyVarsOfType, tcFunResultTy, tidyTopType,
55 mkForAllTys, mkFunTys, mkTyConApp, tcSplitForAllTys
57 import TcMatches ( tcStmtsAndThen, TcStmtCtxt(..) )
58 import Inst ( showLIE )
59 import TcBinds ( tcTopBinds )
60 import TcClassDcl ( tcClassDecls2 )
61 import TcDefaults ( tcDefaults )
62 import TcEnv ( tcExtendGlobalValEnv,
63 tcExtendInstEnv, tcExtendRules,
64 tcLookupTyCon, tcLookupGlobal,
67 import TcRules ( tcRules )
68 import TcForeign ( tcForeignImports, tcForeignExports )
69 import TcIfaceSig ( tcInterfaceSigs, tcCoreBinds )
70 import TcInstDcls ( tcInstDecls1, tcIfaceInstDecls, tcInstDecls2 )
71 import TcSimplify ( tcSimplifyTop, tcSimplifyInfer )
72 import TcTyClsDecls ( tcTyAndClassDecls )
74 import RnNames ( importsFromLocalDecls, rnImports, exportsFromAvail,
76 import RnIfaces ( slurpImpDecls, checkVersions, RecompileRequired, outOfDate )
77 import RnHiFiles ( readIface, loadOldIface )
78 import RnEnv ( lookupSrcName, lookupOccRn, plusGlobalRdrEnv,
79 ubiquitousNames, implicitModuleFVs, implicitStmtFVs, dataTcOccs )
80 import RnExpr ( rnStmts, rnExpr )
81 import RnSource ( rnSrcDecls, checkModDeprec, rnStats )
83 import CoreUnfold ( unfoldingTemplate )
84 import CoreSyn ( IdCoreRule, Bind(..) )
85 import PprCore ( pprIdRules, pprCoreBindings )
86 import TysWiredIn ( mkListTy, unitTy )
87 import ErrUtils ( mkDumpDoc, showPass, pprBagOfErrors )
88 import Id ( Id, mkLocalId, isLocalId, idName, idType, idUnfolding, setIdLocalExported )
89 import IdInfo ( GlobalIdDetails(..) )
90 import Var ( Var, setGlobalIdDetails )
91 import Module ( Module, ModuleName, mkHomeModule, mkModuleName, moduleName, moduleUserString, moduleEnvElts )
92 import OccName ( mkVarOcc )
93 import Name ( Name, isExternalName, getSrcLoc, nameOccName )
94 import NameEnv ( delListFromNameEnv )
96 import TyCon ( tyConGenInfo )
97 import BasicTypes ( EP(..), RecFlag(..) )
98 import SrcLoc ( noSrcLoc )
100 import HscTypes ( PersistentCompilerState(..), InteractiveContext(..),
101 ModIface, ModDetails(..), ModGuts(..),
103 ModIface(..), ModDetails(..), IfaceDecls(..),
104 GhciMode(..), noDependencies,
105 Deprecations(..), plusDeprecs,
107 GenAvailInfo(Avail), availsToNameSet,
109 TypeEnv, TyThing, typeEnvTyCons,
110 extendTypeEnvWithIds, typeEnvIds, typeEnvTyCons,
111 extendLocalRdrEnv, emptyFixityEnv
114 import RdrName ( rdrEnvElts )
115 import RnHiFiles ( loadInterface )
116 import RnEnv ( mkGlobalRdrEnv )
117 import HscTypes ( GlobalRdrElt(..), GlobalRdrEnv, ImportReason(..), Provenance(..),
121 import DATA_IOREF ( readIORef )
122 import FastString ( mkFastString )
123 import Panic ( showException )
124 import List ( partition )
125 import Util ( sortLt )
130 %************************************************************************
132 Typecheck and rename a module
134 %************************************************************************
138 tcRnModule :: HscEnv -> PersistentCompilerState
140 -> IO (PersistentCompilerState, Maybe TcGblEnv)
142 tcRnModule hsc_env pcs
143 (HsModule maybe_mod exports import_decls local_decls mod_deprec loc)
144 = do { showPass (hsc_dflags hsc_env) "Renamer/typechecker" ;
146 let { this_mod = case maybe_mod of
147 Nothing -> mkHomeModule mAIN_Name -- 'module M where' is omitted
148 Just mod -> mod } ; -- The normal case
150 initTc hsc_env pcs this_mod $ addSrcLoc loc $
151 do { -- Deal with imports; sets tcg_rdr_env, tcg_imports
152 (rdr_env, imports) <- rnImports import_decls ;
153 updGblEnv ( \ gbl -> gbl { tcg_rdr_env = rdr_env,
154 tcg_imports = tcg_imports gbl `plusImportAvails` imports })
156 traceRn (text "rn1" <+> ppr (imp_dep_mods imports)) ;
157 -- Fail if there are any errors so far
158 -- The error printing (if needed) takes advantage
159 -- of the tcg_env we have now set
162 traceRn (text "rn1a") ;
163 -- Rename and type check the declarations
164 (tcg_env, src_dus) <- tcRnSrcDecls local_decls ;
165 setGblEnv tcg_env $ do {
167 traceRn (text "rn3") ;
168 -- Check whether the entire module is deprecated
169 -- This happens only once per module
170 -- Returns the full new deprecations; a module deprecation
171 -- over-rides the earlier ones
172 let { mod_deprecs = checkModDeprec mod_deprec } ;
173 updGblEnv (\gbl -> gbl { tcg_deprecs = tcg_deprecs gbl `plusDeprecs` mod_deprecs })
176 -- Process the export list
177 export_avails <- exportsFromAvail maybe_mod exports ;
178 updGblEnv (\gbl -> gbl { tcg_exports = export_avails })
181 -- Get any supporting decls for the exports that have not already
182 -- been sucked in for the declarations in the body of the module.
183 -- (This can happen if something is imported only to be re-exported.)
185 -- Importing these supporting declarations is required
186 -- *only* to gether usage information
187 -- (see comments with MkIface.mkImportInfo for why)
188 -- For OneShot compilation we could just throw away the decls
189 -- but for Batch or Interactive we must put them in the type
190 -- envt because they've been removed from the holding pen
191 let { export_fvs = availsToNameSet export_avails } ;
192 tcg_env <- importSupportingDecls export_fvs ;
193 setGblEnv tcg_env $ do {
195 -- Report unused names
196 let { all_dus = src_dus `plusDU` usesOnly export_fvs } ;
197 reportUnusedNames tcg_env all_dus ;
199 -- Dump output and return
206 %*********************************************************
208 \subsection{Closing up the interface decls}
210 %*********************************************************
212 Suppose we discover we don't need to recompile. Then we start from the
213 IfaceDecls in the ModIface, and fluff them up by sucking in all the decls they need.
217 -> PersistentCompilerState
218 -> ModIface -- Get the decls from here
219 -> IO (PersistentCompilerState, Maybe ModDetails)
220 -- Nothing <=> errors happened
221 tcRnIface hsc_env pcs
222 (ModIface {mi_module = mod, mi_decls = iface_decls})
223 = initTc hsc_env pcs mod $ do {
225 -- Get the supporting decls, and typecheck them all together
226 -- so that any mutually recursive types are done right
227 extra_decls <- slurpImpDecls needed ;
228 env <- typecheckIfaceDecls (group `addImpDecls` extra_decls) ;
230 returnM (ModDetails { md_types = tcg_type_env env,
231 md_insts = tcg_insts env,
232 md_rules = hsCoreRules (tcg_rules env)
233 -- All the rules from an interface are of the IfaceRuleOut form
236 rule_decls = dcl_rules iface_decls
237 inst_decls = dcl_insts iface_decls
238 tycl_decls = dcl_tycl iface_decls
239 group = emptyGroup { hs_ruleds = rule_decls,
240 hs_instds = inst_decls,
241 hs_tyclds = tycl_decls }
242 needed = unionManyNameSets (map ruleDeclFVs rule_decls) `unionNameSets`
243 unionManyNameSets (map instDeclFVs inst_decls) `unionNameSets`
244 unionManyNameSets (map tyClDeclFVs tycl_decls) `unionNameSets`
246 -- Data type decls with record selectors,
247 -- which may appear in the decls, need unpackCString
248 -- and friends. It's easier to just grab them right now.
250 hsCoreRules :: [TypecheckedRuleDecl] -> [IdCoreRule]
251 -- All post-typechecking Iface rules have the form IfaceRuleOut
252 hsCoreRules rules = [(id,rule) | IfaceRuleOut id rule <- rules]
256 %************************************************************************
258 The interactive interface
260 %************************************************************************
264 tcRnStmt :: HscEnv -> PersistentCompilerState
265 -> InteractiveContext
267 -> IO (PersistentCompilerState,
268 Maybe (InteractiveContext, [Name], TypecheckedHsExpr))
269 -- The returned [Name] is the same as the input except for
270 -- ExprStmt, in which case the returned [Name] is [itName]
272 -- The returned TypecheckedHsExpr is of type IO [ () ],
273 -- a list of the bound values, coerced to ().
275 tcRnStmt hsc_env pcs ictxt rdr_stmt
276 = initTc hsc_env pcs iNTERACTIVE $
277 setInteractiveContext ictxt $ do {
279 -- Rename; use CmdLineMode because tcRnStmt is only used interactively
280 ([rn_stmt], fvs) <- initRnInteractive ictxt
281 (rnStmts DoExpr [rdr_stmt]) ;
282 traceRn (text "tcRnStmt" <+> vcat [ppr rdr_stmt, ppr rn_stmt, ppr fvs]) ;
285 -- Suck in the supporting declarations and typecheck them
286 tcg_env <- importSupportingDecls (fvs `plusFV` implicitStmtFVs fvs) ;
287 -- NB: an earlier version deleted (rdrEnvElts local_env) from
288 -- the fvs. But (a) that isn't necessary, because previously
289 -- bound things in the local_env will be in the TypeEnv, and
290 -- the renamer doesn't re-slurp such things, and
291 -- (b) it's WRONG to delete them. Consider in GHCi:
292 -- Mod> let x = e :: T
293 -- Mod> let y = x + 3
294 -- We need to pass 'x' among the fvs to slurpImpDecls, so that
295 -- the latter can see that T is a gate, and hence import the Num T
296 -- instance decl. (See the InTypEnv case in RnIfaces.slurpSourceRefs.)
297 setGblEnv tcg_env $ do {
299 -- The real work is done here
300 ((bound_ids, tc_expr), lie) <- getLIE (tcUserStmt rn_stmt) ;
302 traceTc (text "tcs 1") ;
303 let { -- Make all the bound ids "global" ids, now that
304 -- they're notionally top-level bindings. This is
305 -- important: otherwise when we come to compile an expression
306 -- using these ids later, the byte code generator will consider
307 -- the occurrences to be free rather than global.
308 global_ids = map globaliseId bound_ids ;
309 globaliseId id = setGlobalIdDetails id VanillaGlobal ;
311 -- Update the interactive context
312 rn_env = ic_rn_local_env ictxt ;
313 type_env = ic_type_env ictxt ;
315 bound_names = map idName global_ids ;
316 new_rn_env = extendLocalRdrEnv rn_env bound_names ;
318 -- Remove any shadowed bindings from the type_env;
319 -- they are inaccessible but might, I suppose, cause
320 -- a space leak if we leave them there
321 shadowed = [ n | name <- bound_names,
322 let rdr_name = mkRdrUnqual (nameOccName name),
323 Just n <- [lookupRdrEnv rn_env rdr_name] ] ;
325 filtered_type_env = delListFromNameEnv type_env shadowed ;
326 new_type_env = extendTypeEnvWithIds filtered_type_env global_ids ;
328 new_ic = ictxt { ic_rn_local_env = new_rn_env,
329 ic_type_env = new_type_env }
332 dumpOptTcRn Opt_D_dump_tc
333 (vcat [text "Bound Ids" <+> pprWithCommas ppr global_ids,
334 text "Typechecked expr" <+> ppr tc_expr]) ;
336 returnM (new_ic, bound_names, tc_expr)
341 Here is the grand plan, implemented in tcUserStmt
343 What you type The IO [HValue] that hscStmt returns
344 ------------- ------------------------------------
345 let pat = expr ==> let pat = expr in return [coerce HVal x, coerce HVal y, ...]
348 pat <- expr ==> expr >>= \ pat -> return [coerce HVal x, coerce HVal y, ...]
351 expr (of IO type) ==> expr >>= \ v -> return [coerce HVal v]
352 [NB: result not printed] bindings: [it]
354 expr (of non-IO type, ==> let v = expr in print v >> return [coerce HVal v]
355 result showable) bindings: [it]
357 expr (of non-IO type,
358 result not showable) ==> error
362 ---------------------------
363 tcUserStmt :: RenamedStmt -> TcM ([Id], TypecheckedHsExpr)
364 tcUserStmt (ExprStmt expr _ loc)
365 = newUnique `thenM` \ uniq ->
367 fresh_it = itName uniq
368 the_bind = FunMonoBind fresh_it False
369 [ mkSimpleMatch [] expr placeHolderType loc ] loc
371 tryTcLIE_ (do { -- Try this if the other fails
372 traceTc (text "tcs 1b") ;
374 LetStmt (MonoBind the_bind [] NonRecursive),
375 ExprStmt (HsApp (HsVar printName) (HsVar fresh_it))
376 placeHolderType loc] })
377 (do { -- Try this first
378 traceTc (text "tcs 1a") ;
379 tc_stmts [BindStmt (VarPat fresh_it) expr loc] })
381 tcUserStmt stmt = tc_stmts [stmt]
383 ---------------------------
385 = do { ioTyCon <- tcLookupTyCon ioTyConName ;
387 ret_ty = mkListTy unitTy ;
388 names = collectStmtsBinders stmts ;
390 stmt_ctxt = SC { sc_what = DoExpr,
392 sc_body = check_body,
395 check_rhs rhs rhs_ty = tcCheckRho rhs (mkTyConApp ioTyCon [rhs_ty]) ;
396 check_body body = tcCheckRho body (mkTyConApp ioTyCon [ret_ty]) ;
398 -- ret_expr is the expression
399 -- returnIO [coerce () x, .., coerce () z]
400 ret_stmt = ResultStmt ret_expr noSrcLoc ;
401 ret_expr = HsApp (HsVar returnIOName)
402 (ExplicitList placeHolderType (map mk_item names)) ;
403 mk_item name = HsApp (HsVar unsafeCoerceName) (HsVar name) ;
405 all_stmts = stmts ++ [ret_stmt]
408 -- OK, we're ready to typecheck the stmts
409 traceTc (text "tcs 2") ;
410 ((ids, tc_stmts), lie) <-
412 tcStmtsAndThen combine stmt_ctxt all_stmts $
414 -- Look up the names right in the middle,
415 -- where they will all be in scope
416 ids <- mappM tcLookupId names ;
420 -- Simplify the context right here, so that we fail
421 -- if there aren't enough instances. Notably, when we see
423 -- we use recoverTc_ to try it <- e
424 -- and then let it = e
425 -- It's the simplify step that rejects the first.
426 traceTc (text "tcs 3") ;
427 const_binds <- tcSimplifyTop lie ;
429 -- Build result expression and zonk it
430 io_ids <- mappM mk_rebound
431 [returnIOName, failIOName, bindIOName, thenIOName] ;
432 let { expr = mkHsLet const_binds $
433 HsDo DoExpr tc_stmts io_ids
434 (mkTyConApp ioTyCon [ret_ty]) noSrcLoc } ;
435 zonked_expr <- zonkTopExpr expr ;
436 zonked_ids <- zonkTopBndrs ids ;
438 return (zonked_ids, zonked_expr)
441 combine stmt (ids, stmts) = (ids, stmt:stmts)
442 mk_rebound n = do { id <- tcLookupId n; return (n, HsVar id) }
447 tcRnExpr just finds the type of an expression
450 tcRnExpr :: HscEnv -> PersistentCompilerState
451 -> InteractiveContext
453 -> IO (PersistentCompilerState, Maybe Type)
454 tcRnExpr hsc_env pcs ictxt rdr_expr
455 = initTc hsc_env pcs iNTERACTIVE $
456 setInteractiveContext ictxt $ do {
458 (rn_expr, fvs) <- initRnInteractive ictxt (rnExpr rdr_expr) ;
461 -- Suck in the supporting declarations and typecheck them
462 tcg_env <- importSupportingDecls (fvs `plusFV` ubiquitousNames) ;
463 setGblEnv tcg_env $ do {
465 -- Now typecheck the expression;
466 -- it might have a rank-2 type (e.g. :t runST)
467 ((tc_expr, res_ty), lie) <- getLIE (tcInferRho rn_expr) ;
468 ((qtvs, _, dict_ids), lie_top) <- getLIE (tcSimplifyInfer smpl_doc (tyVarsOfType res_ty) lie) ;
469 tcSimplifyTop lie_top ;
471 let { all_expr_ty = mkForAllTys qtvs $
472 mkFunTys (map idType dict_ids) $
474 zonkTcType all_expr_ty
477 smpl_doc = ptext SLIT("main expression")
482 tcRnThing :: HscEnv -> PersistentCompilerState
483 -> InteractiveContext
485 -> IO (PersistentCompilerState, Maybe [TyThing])
486 -- Look up a RdrName and return all the TyThings it might be
487 -- We treat a capitalised RdrName as both a data constructor
488 -- and as a type or class constructor; hence we return up to two results
489 tcRnThing hsc_env pcs ictxt rdr_name
490 = initTc hsc_env pcs iNTERACTIVE $
491 setInteractiveContext ictxt $ do {
493 -- If the identifier is a constructor (begins with an
494 -- upper-case letter), then we need to consider both
495 -- constructor and type class identifiers.
496 let { rdr_names = dataTcOccs rdr_name } ;
498 -- results :: [(Messages, Maybe Name)]
499 results <- initRnInteractive ictxt
500 (mapM (tryTc . lookupOccRn) rdr_names) ;
502 -- The successful lookups will be (Just name)
503 let { (warns_s, good_names) = unzip [ (msgs, name)
504 | (msgs, Just name) <- results] ;
505 errs_s = [msgs | (msgs, Nothing) <- results] } ;
507 -- Fail if nothing good happened, else add warnings
508 if null good_names then -- Fail
509 do { addMessages (head errs_s) ; failM }
510 else -- Add deprecation warnings
511 mapM_ addMessages warns_s ;
513 -- Slurp in the supporting declarations
514 tcg_env <- importSupportingDecls (mkFVs good_names) ;
515 setGblEnv tcg_env $ do {
517 -- And lookup up the entities
518 mapM tcLookupGlobal good_names
524 setInteractiveContext :: InteractiveContext -> TcRn m a -> TcRn m a
525 setInteractiveContext icxt thing_inside
526 = traceTc (text "setIC" <+> ppr (ic_type_env icxt)) `thenM_`
527 updGblEnv (\ env -> env { tcg_rdr_env = ic_rn_gbl_env icxt,
528 tcg_type_env = ic_type_env icxt })
531 initRnInteractive :: InteractiveContext -> RnM a -> TcM a
532 -- Set the local RdrEnv from the interactive context
533 initRnInteractive ictxt rn_thing
534 = initRn CmdLineMode $
535 setLocalRdrEnv (ic_rn_local_env ictxt) $
540 %************************************************************************
542 Type-checking external-core modules
544 %************************************************************************
547 tcRnExtCore :: HscEnv -> PersistentCompilerState
549 -> IO (PersistentCompilerState, Maybe ModGuts)
550 -- Nothing => some error occurred
552 tcRnExtCore hsc_env pcs (HsModule (Just this_mod) _ _ decls _ loc)
553 -- For external core, the module name is syntactically reqd
554 -- Rename the (Core) module. It's a bit like an interface
555 -- file: all names are original names
556 = do { showPass (hsc_dflags hsc_env) "Renamer/typechecker" ;
558 initTc hsc_env pcs this_mod $ addSrcLoc loc $ do {
560 -- Rename the source, only in interface mode.
561 -- rnSrcDecls handles fixity decls etc too, which won't occur
562 -- but that doesn't matter
563 let { local_group = mkGroup decls } ;
564 (_, rn_decls, dus) <- initRn (InterfaceMode this_mod)
565 (rnSrcDecls local_group) ;
568 -- Get the supporting decls
569 rn_imp_decls <- slurpImpDecls (duUses dus) ;
570 let { rn_decls = rn_decls `addImpDecls` rn_imp_decls } ;
572 -- Dump trace of renaming part
573 rnDump (ppr rn_decls) ;
574 rnStats rn_imp_decls ;
576 -- Typecheck them all together so that
577 -- any mutually recursive types are done right
578 tcg_env <- typecheckIfaceDecls rn_decls ;
579 setGblEnv tcg_env $ do {
581 -- Now the core bindings
582 core_prs <- tcCoreBinds (hs_coreds rn_decls) ;
583 tcExtendGlobalValEnv (map fst core_prs) $ do {
587 bndrs = map fst core_prs ;
588 my_exports = map (Avail . idName) bndrs ;
589 -- ToDo: export the data types also?
591 final_type_env = extendTypeEnvWithIds (tcg_type_env tcg_env) bndrs ;
593 mod_guts = ModGuts { mg_module = this_mod,
594 mg_usages = [], -- ToDo: compute usage
595 mg_dir_imps = [], -- ??
596 mg_deps = noDependencies, -- ??
597 mg_exports = my_exports,
598 mg_types = final_type_env,
599 mg_insts = tcg_insts tcg_env,
600 mg_rules = hsCoreRules (tcg_rules tcg_env),
601 mg_binds = [Rec core_prs],
604 mg_rdr_env = emptyGlobalRdrEnv,
605 mg_fix_env = emptyFixityEnv,
606 mg_deprecs = NoDeprecs,
610 tcCoreDump mod_guts ;
617 %************************************************************************
619 Type-checking the top level of a module
621 %************************************************************************
624 tcRnSrcDecls :: [RdrNameHsDecl] -> TcM (TcGblEnv, DefUses)
625 -- Returns the variables free in the decls
626 -- Reason: solely to report unused imports and bindings
628 = do { -- Do all the declarations
629 ((tc_envs, dus), lie) <- getLIE (tc_rn_src_decls decls) ;
631 -- tcSimplifyTop deals with constant or ambiguous InstIds.
632 -- How could there be ambiguous ones? They can only arise if a
633 -- top-level decl falls under the monomorphism
634 -- restriction, and no subsequent decl instantiates its
635 -- type. (Usually, ambiguous type variables are resolved
636 -- during the generalisation step.)
637 traceTc (text "Tc8") ;
638 setEnvs tc_envs $ do {
639 -- Setting the global env exposes the instances to tcSimplifyTop
640 -- Setting the local env exposes the local Ids, so that
641 -- we get better error messages (monomorphism restriction)
642 inst_binds <- tcSimplifyTop lie ;
644 -- Backsubstitution. This must be done last.
645 -- Even tcSimplifyTop may do some unification.
646 traceTc (text "Tc9") ;
647 let { (tcg_env, _) = tc_envs ;
648 TcGblEnv { tcg_type_env = type_env, tcg_binds = binds,
649 tcg_rules = rules, tcg_fords = fords } = tcg_env } ;
651 (bind_ids, binds', fords', rules') <- zonkTopDecls (binds `andMonoBinds` inst_binds)
654 return (tcg_env { tcg_type_env = extendTypeEnvWithIds type_env bind_ids,
655 tcg_binds = binds', tcg_rules = rules', tcg_fords = fords' },
659 tc_rn_src_decls :: [RdrNameHsDecl] -> TcM ((TcGblEnv, TcLclEnv), DefUses)
662 = do { let { (first_group, group_tail) = findSplice ds } ;
663 -- If ds is [] we get ([], Nothing)
665 -- Type check the decls up to, but not including, the first splice
666 (tc_envs@(_,tcl_env), src_dus1) <- tcRnGroup first_group ;
668 -- Bale out if errors; for example, error recovery when checking
669 -- the RHS of 'main' can mean that 'main' is not in the envt for
670 -- the subsequent checkMain test
675 -- If there is no splice, we're nearly done
677 Nothing -> do { -- Last thing: check for `main'
678 (tcg_env, main_fvs) <- checkMain ;
679 return ((tcg_env, tcl_env),
680 src_dus1 `plusDU` usesOnly main_fvs)
683 -- If there's a splice, we must carry on
684 Just (SpliceDecl splice_expr splice_loc, rest_ds) -> do {
686 failWithTc (text "Can't do a top-level splice; need a bootstrapped compiler")
689 -- Rename the splice expression, and get its supporting decls
690 (rn_splice_expr, splice_fvs) <- initRn SourceMode $
691 addSrcLoc splice_loc $
693 tcg_env <- importSupportingDecls (splice_fvs `plusFV` templateHaskellNames) ;
694 setGblEnv tcg_env $ do {
696 -- Execute the splice
697 spliced_decls <- tcSpliceDecls rn_splice_expr ;
699 -- Glue them on the front of the remaining decls and loop
700 (tc_envs, src_dus2) <- tc_rn_src_decls (spliced_decls ++ rest_ds) ;
702 return (tc_envs, src_dus1 `plusDU` usesOnly splice_fvs `plusDU` src_dus2)
709 %************************************************************************
711 Type-checking the top level of a module
713 %************************************************************************
715 tcRnGroup takes a bunch of top-level source-code declarations, and
717 * gets supporting declarations from interface files
720 * and augments the TcGblEnv with the results
722 In Template Haskell it may be called repeatedly for each group of
723 declarations. It expects there to be an incoming TcGblEnv in the
724 monad; it augments it and returns the new TcGblEnv.
727 tcRnGroup :: HsGroup RdrName -> TcM ((TcGblEnv, TcLclEnv), DefUses)
728 -- Returns the variables free in the decls, for unused-binding reporting
730 = do { -- Rename the declarations
731 (tcg_env, rn_decls, src_dus) <- rnTopSrcDecls decls ;
732 setGblEnv tcg_env $ do {
734 -- Typecheck the declarations
735 tc_envs <- tcTopSrcDecls rn_decls ;
737 return (tc_envs, src_dus)
740 ------------------------------------------------
741 rnTopSrcDecls :: HsGroup RdrName -> TcM (TcGblEnv, HsGroup Name, DefUses)
743 = do { -- Bring top level binders into scope
744 (rdr_env, imports) <- importsFromLocalDecls group ;
745 updGblEnv (\gbl -> gbl { tcg_rdr_env = rdr_env `plusGlobalRdrEnv`
747 tcg_imports = imports `plusImportAvails`
751 failIfErrsM ; -- No point in continuing if (say) we have duplicate declarations
753 -- Rename the source decls
754 (tcg_env, rn_src_decls, src_dus) <- initRn SourceMode (rnSrcDecls group) ;
755 setGblEnv tcg_env $ do {
759 -- Import consquential imports
760 let { src_fvs = duUses src_dus } ;
761 rn_imp_decls <- slurpImpDecls (src_fvs `plusFV` implicitModuleFVs src_fvs) ;
762 let { rn_decls = rn_src_decls `addImpDecls` rn_imp_decls } ;
764 -- Dump trace of renaming part
765 rnDump (ppr rn_decls) ;
766 rnStats rn_imp_decls ;
768 return (tcg_env, rn_decls, src_dus)
771 ------------------------------------------------
772 tcTopSrcDecls :: HsGroup Name -> TcM (TcGblEnv, TcLclEnv)
774 (HsGroup { hs_tyclds = tycl_decls,
775 hs_instds = inst_decls,
776 hs_fords = foreign_decls,
777 hs_defds = default_decls,
778 hs_ruleds = rule_decls,
779 hs_valds = val_binds })
780 = do { -- Type-check the type and class decls, and all imported decls
781 -- The latter come in via tycl_decls
782 traceTc (text "Tc2") ;
783 tcg_env <- tcTyClDecls tycl_decls ;
784 setGblEnv tcg_env $ do {
786 -- Source-language instances, including derivings,
787 -- and import the supporting declarations
788 traceTc (text "Tc3") ;
789 (tcg_env, inst_infos, deriv_binds, fvs) <- tcInstDecls1 tycl_decls inst_decls ;
790 setGblEnv tcg_env $ do {
791 tcg_env <- importSupportingDecls fvs ;
792 setGblEnv tcg_env $ do {
794 -- Foreign import declarations next. No zonking necessary
795 -- here; we can tuck them straight into the global environment.
796 traceTc (text "Tc4") ;
797 (fi_ids, fi_decls) <- tcForeignImports foreign_decls ;
798 tcExtendGlobalValEnv fi_ids $
799 updGblEnv (\gbl -> gbl { tcg_fords = tcg_fords gbl ++ fi_decls })
802 -- Default declarations
803 traceTc (text "Tc4a") ;
804 default_tys <- tcDefaults default_decls ;
805 updGblEnv (\gbl -> gbl { tcg_default = default_tys }) $ do {
807 -- Value declarations next
808 -- We also typecheck any extra binds that came out
809 -- of the "deriving" process
810 traceTc (text "Tc5") ;
811 (tc_val_binds, lcl_env) <- tcTopBinds (val_binds `ThenBinds` deriv_binds) ;
812 setLclTypeEnv lcl_env $ do {
814 -- Second pass over class and instance declarations,
815 -- plus rules and foreign exports, to generate bindings
816 traceTc (text "Tc6") ;
817 (cls_dm_binds, dm_ids) <- tcClassDecls2 tycl_decls ;
818 tcExtendGlobalValEnv dm_ids $ do {
819 inst_binds <- tcInstDecls2 inst_infos ;
820 showLIE (text "after instDecls2") ;
823 -- They need to be zonked, so we return them
824 traceTc (text "Tc7") ;
825 (foe_binds, foe_decls) <- tcForeignExports foreign_decls ;
828 -- Need to partition them because the source rules
829 -- must be zonked before adding them to tcg_rules
830 -- NB: built-in rules come in as IfaceRuleOut's, and
831 -- get added to tcg_rules right here by tcExtendRules
832 rules <- tcRules rule_decls ;
833 let { (src_rules, iface_rules) = partition isSrcRule rules } ;
834 tcExtendRules iface_rules $ do {
837 tcg_env <- getGblEnv ;
838 let { all_binds = tc_val_binds `AndMonoBinds`
839 inst_binds `AndMonoBinds`
840 cls_dm_binds `AndMonoBinds`
843 -- Extend the GblEnv with the (as yet un-zonked)
844 -- bindings, rules, foreign decls
845 tcg_env' = tcg_env { tcg_binds = tcg_binds tcg_env `andMonoBinds` all_binds,
846 tcg_rules = tcg_rules tcg_env ++ src_rules,
847 tcg_fords = tcg_fords tcg_env ++ foe_decls } } ;
849 return (tcg_env', lcl_env)
854 tcTyClDecls :: [RenamedTyClDecl]
857 -- tcTyClDecls deals with
858 -- type and class decls (some source, some imported)
859 -- interface signatures (checked lazily)
861 -- It returns the TcGblEnv for this module, and side-effects the
862 -- persistent compiler state to reflect the things imported from
865 tcTyClDecls tycl_decls
867 -- tcTyAndClassDecls recovers internally, but if anything gave rise to
868 -- an error we'd better stop now, to avoid a cascade
870 traceTc (text "TyCl1") `thenM_`
871 tcTyAndClassDecls tycl_decls `thenM` \ tcg_env ->
872 -- Returns the extended environment
875 traceTc (text "TyCl2") `thenM_`
876 tcInterfaceSigs tycl_decls `thenM` \ tcg_env ->
877 -- Returns the extended environment
884 %************************************************************************
886 Load the old interface file for this module (unless
887 we have it aleady), and check whether it is up to date
890 %************************************************************************
893 checkOldIface :: HscEnv
894 -> PersistentCompilerState
896 -> FilePath -- Where the interface file is
897 -> Bool -- Source unchanged
898 -> Maybe ModIface -- Old interface from compilation manager, if any
899 -> IO (PersistentCompilerState, Maybe (RecompileRequired, Maybe ModIface))
900 -- Nothing <=> errors happened
902 checkOldIface hsc_env pcs mod iface_path source_unchanged maybe_iface
903 = do { showPass (hsc_dflags hsc_env)
904 ("Checking old interface for " ++ moduleUserString mod) ;
906 initTc hsc_env pcs mod
907 (check_old_iface iface_path source_unchanged maybe_iface)
910 check_old_iface iface_path source_unchanged maybe_iface
911 = -- CHECK WHETHER THE SOURCE HAS CHANGED
912 ifM (not source_unchanged)
913 (traceHiDiffs (nest 4 (text "Source file changed or recompilation check turned off")))
916 -- If the source has changed and we're in interactive mode, avoid reading
917 -- an interface; just return the one we might have been supplied with.
918 getGhciMode `thenM` \ ghci_mode ->
919 if (ghci_mode == Interactive) && not source_unchanged then
920 returnM (outOfDate, maybe_iface)
923 case maybe_iface of {
924 Just old_iface -> -- Use the one we already have
925 checkVersions source_unchanged old_iface `thenM` \ recomp ->
926 returnM (recomp, Just old_iface)
930 -- Try and read the old interface for the current module
931 -- from the .hi file left from the last time we compiled it
932 getModule `thenM` \ this_mod ->
933 readIface this_mod iface_path False `thenM` \ read_result ->
934 case read_result of {
935 Left err -> -- Old interface file not found, or garbled; give up
936 traceHiDiffs (text "FYI: cannot read old interface file:"
937 $$ nest 4 (text (showException err))) `thenM_`
938 returnM (outOfDate, Nothing)
940 ; Right parsed_iface ->
942 -- We found the file and parsed it; now load it
943 tryTc (initRn (InterfaceMode this_mod)
944 (loadOldIface parsed_iface)) `thenM` \ ((_,errs), mb_iface) ->
946 Nothing -> -- Something went wrong in loading. The main likely thing
947 -- is that the usages mentioned B.f, where B.hi and B.hs no
948 -- longer exist. Then newGlobalName2 fails with an error message
949 -- This isn't an error; we just don't have an old iface file to
950 -- look at. Spit out a traceHiDiffs for info though.
951 traceHiDiffs (text "FYI: loading old interface file failed"
952 $$ nest 4 (docToSDoc (pprBagOfErrors errs))) `thenM_`
953 return (outOfDate, Nothing)
957 -- At last, we have got the old iface; check its versions
958 checkVersions source_unchanged iface `thenM` \ recomp ->
959 returnM (recomp, Just iface)
964 %************************************************************************
966 Type-check and rename supporting declarations
967 This is used to deal with the free vars of a splice,
968 or derived code: slurp in the necessary declarations,
969 typecheck them, and add them to the EPS
971 %************************************************************************
974 importSupportingDecls :: FreeVars -> TcM TcGblEnv
975 -- Completely deal with the supporting imports needed
976 -- by the specified free-var set
977 importSupportingDecls fvs
978 = do { traceRn (text "Import supporting decls for" <+> ppr (nameSetToList fvs)) ;
979 decls <- slurpImpDecls fvs ;
980 traceRn (text "...namely:" <+> vcat (map ppr decls)) ;
981 typecheckIfaceDecls (mkGroup decls) }
983 typecheckIfaceDecls :: HsGroup Name -> TcM TcGblEnv
984 -- The decls are all interface-file declarations
985 -- Usually they are all from other modules, but when we are reading
986 -- this module's interface from a file, it's possible that some of
987 -- them are for the module being compiled.
988 -- That is why the tcExtendX functions need to do partitioning.
990 -- If all the decls are from other modules, the returned TcGblEnv
991 -- will have an empty tc_genv, but its tc_inst_env
992 -- cache may have been augmented.
993 typecheckIfaceDecls (HsGroup { hs_tyclds = tycl_decls,
994 hs_instds = inst_decls,
995 hs_ruleds = rule_decls })
996 = do { -- Typecheck the type, class, and interface-sig decls
997 tcg_env <- tcTyClDecls tycl_decls ;
998 setGblEnv tcg_env $ do {
1000 -- Typecheck the instance decls, and rules
1001 -- Note that imported dictionary functions are already
1002 -- in scope from the preceding tcTyClDecls
1003 tcIfaceInstDecls inst_decls `thenM` \ dfuns ->
1004 tcExtendInstEnv dfuns $
1005 tcRules rule_decls `thenM` \ rules ->
1006 tcExtendRules rules $
1008 getGblEnv -- Return the environment
1014 %*********************************************************
1016 mkGlobalContext: make up an interactive context
1018 Used for initialising the lexical environment
1019 of the interactive read-eval-print loop
1021 %*********************************************************
1026 :: HscEnv -> PersistentCompilerState
1027 -> [Module] -- Expose these modules' top-level scope
1028 -> [Module] -- Expose these modules' exports only
1029 -> IO (PersistentCompilerState, Maybe GlobalRdrEnv)
1031 mkGlobalContext hsc_env pcs toplevs exports
1032 = initTc hsc_env pcs iNTERACTIVE $ do {
1034 toplev_envs <- mappM getTopLevScope toplevs ;
1035 export_envs <- mappM getModuleExports exports ;
1036 returnM (foldr plusGlobalRdrEnv emptyGlobalRdrEnv
1037 (toplev_envs ++ export_envs))
1040 getTopLevScope :: Module -> TcRn m GlobalRdrEnv
1042 = do { iface <- loadInterface contextDoc (moduleName mod) (ImportByUser False) ;
1043 case mi_globals iface of
1044 Nothing -> panic "getTopLevScope"
1045 Just env -> returnM env }
1047 getModuleExports :: Module -> TcRn m GlobalRdrEnv
1048 getModuleExports mod
1049 = do { iface <- loadInterface contextDoc (moduleName mod) (ImportByUser False) ;
1050 returnM (foldl add emptyGlobalRdrEnv (mi_exports iface)) }
1052 prov_fn n = NonLocalDef ImplicitImport
1053 add env (mod,avails)
1054 = plusGlobalRdrEnv env (mkGlobalRdrEnv mod True prov_fn avails NoDeprecs)
1056 contextDoc = text "context for compiling statements"
1062 -> PersistentCompilerState -- IN: persistent compiler state
1063 -> Module -- module to inspect
1064 -> Bool -- grab just the exports, or the whole toplev
1065 -> IO (PersistentCompilerState, Maybe [TyThing])
1067 getModuleContents hsc_env pcs mod exports_only
1068 = initTc hsc_env pcs iNTERACTIVE $ do {
1070 -- Load the interface if necessary (a home module will certainly
1071 -- alraedy be loaded, but a package module might not be)
1072 iface <- loadInterface contextDoc (moduleName mod) (ImportByUser False) ;
1074 let { export_names = availsToNameSet export_avails ;
1075 export_avails = [ avail | (mn, avails) <- mi_exports iface,
1076 avail <- avails ] } ;
1078 all_names <- if exports_only then
1080 else case mi_globals iface of {
1082 return (get_locals rdr_env) ;
1084 Nothing -> do { addErr (noRdrEnvErr mod) ;
1085 return export_names } } ;
1086 -- Invariant; we only have (not exports_only)
1087 -- for a home module so it must already be in the HIT
1088 -- So the Nothing case is a bug
1090 env <- importSupportingDecls all_names ;
1091 setGblEnv env (mappM tcLookupGlobal (nameSetToList all_names))
1094 -- Grab all the things from the global env that are locally def'd
1095 get_locals rdr_env = mkNameSet [ gre_name gre
1096 | elts <- rdrEnvElts rdr_env,
1099 -- Make a set because a name is often in the envt in
1100 -- both qualified and unqualified forms
1102 noRdrEnvErr mod = ptext SLIT("No top-level environment available for module")
1103 <+> quotes (ppr mod)
1107 %************************************************************************
1111 %************************************************************************
1115 = do { ghci_mode <- getGhciMode ;
1116 tcg_env <- getGblEnv ;
1118 mb_main_mod <- readMutVar v_MainModIs ;
1119 mb_main_fn <- readMutVar v_MainFunIs ;
1120 let { main_mod = case mb_main_mod of {
1121 Just mod -> mkModuleName mod ;
1122 Nothing -> mAIN_Name } ;
1123 main_fn = case mb_main_fn of {
1124 Just fn -> mkRdrUnqual (mkVarOcc (mkFastString fn)) ;
1125 Nothing -> main_RDR_Unqual } } ;
1127 check_main ghci_mode tcg_env main_mod main_fn
1131 check_main ghci_mode tcg_env main_mod main_fn
1132 -- If we are in module Main, check that 'main' is defined.
1133 -- It may be imported from another module, in which case
1134 -- we have to drag in its.
1136 -- Also form the definition
1137 -- $main = runIO main
1138 -- so we need to slurp in runIO too.
1140 -- ToDo: We have to return the main_name separately, because it's a
1141 -- bona fide 'use', and should be recorded as such, but the others
1144 -- Blimey: a whole page of code to do this...
1146 | mod_name /= main_mod
1147 = return (tcg_env, emptyFVs)
1149 -- Check that 'main' is in scope
1150 -- It might be imported from another module!
1152 -- We use a guard for this (rather than letting lookupSrcName fail)
1153 -- because it's not an error in ghci)
1154 | not (main_fn `elemRdrEnv` rdr_env)
1155 = do { complain_no_main; return (tcg_env, emptyFVs) }
1157 | otherwise -- OK, so the appropriate 'main' is in scope
1159 = do { main_name <- lookupSrcName main_fn ;
1161 tcg_env <- importSupportingDecls (unitFV runIOName) ;
1163 addSrcLoc (getSrcLoc main_name) $
1164 addErrCtxt mainCtxt $
1165 setGblEnv tcg_env $ do {
1167 -- $main :: IO () = runIO main
1168 let { rhs = HsApp (HsVar runIOName) (HsVar main_name) } ;
1169 (main_expr, ty) <- tcInferRho rhs ;
1171 let { dollar_main_id = setIdLocalExported (mkLocalId dollarMainName ty) ;
1172 main_bind = VarMonoBind dollar_main_id main_expr ;
1173 tcg_env' = tcg_env { tcg_binds = tcg_binds tcg_env
1174 `andMonoBinds` main_bind } } ;
1176 return (tcg_env', unitFV main_name)
1179 mod_name = moduleName (tcg_mod tcg_env)
1180 rdr_env = tcg_rdr_env tcg_env
1182 complain_no_main | ghci_mode == Interactive = return ()
1183 | otherwise = failWithTc noMainMsg
1184 -- In interactive mode, don't worry about the absence of 'main'
1185 -- In other modes, fail altogether, so that we don't go on
1186 -- and complain a second time when processing the export list.
1188 mainCtxt = ptext SLIT("When checking the type of the main function") <+> quotes (ppr main_fn)
1189 noMainMsg = ptext SLIT("The main function") <+> quotes (ppr main_fn)
1190 <+> ptext SLIT("is not defined in module") <+> quotes (ppr main_mod)
1194 %************************************************************************
1198 %************************************************************************
1201 rnDump :: SDoc -> TcRn m ()
1202 -- Dump, with a banner, if -ddump-rn
1203 rnDump doc = dumpOptTcRn Opt_D_dump_rn (mkDumpDoc "Renamer" doc)
1205 tcDump :: TcGblEnv -> TcRn m ()
1207 = do { dflags <- getDOpts ;
1209 -- Dump short output if -ddump-types or -ddump-tc
1210 ifM (dopt Opt_D_dump_types dflags || dopt Opt_D_dump_tc dflags)
1211 (dumpTcRn short_dump) ;
1213 -- Dump bindings if -ddump-tc
1214 dumpOptTcRn Opt_D_dump_tc (mkDumpDoc "Typechecker" full_dump)
1217 short_dump = pprTcGblEnv env
1218 full_dump = ppr (tcg_binds env)
1219 -- NB: foreign x-d's have undefined's in their types;
1220 -- hence can't show the tc_fords
1223 = do { dflags <- getDOpts ;
1224 ifM (dopt Opt_D_dump_types dflags || dopt Opt_D_dump_tc dflags)
1225 (dumpTcRn (pprModGuts mod_guts)) ;
1227 -- Dump bindings if -ddump-tc
1228 dumpOptTcRn Opt_D_dump_tc (mkDumpDoc "Typechecker" full_dump) }
1230 full_dump = pprCoreBindings (mg_binds mod_guts)
1232 -- It's unpleasant having both pprModGuts and pprModDetails here
1233 pprTcGblEnv :: TcGblEnv -> SDoc
1234 pprTcGblEnv (TcGblEnv { tcg_type_env = type_env,
1235 tcg_insts = dfun_ids,
1237 tcg_imports = imports })
1238 = vcat [ ppr_types dfun_ids type_env
1239 , ppr_insts dfun_ids
1240 , vcat (map ppr rules)
1241 , ppr_gen_tycons (typeEnvTyCons type_env)
1242 , ptext SLIT("Dependent modules:") <+> ppr (moduleEnvElts (imp_dep_mods imports))
1243 , ptext SLIT("Dependent packages:") <+> ppr (imp_dep_pkgs imports)]
1245 pprModGuts :: ModGuts -> SDoc
1246 pprModGuts (ModGuts { mg_types = type_env,
1248 = vcat [ ppr_types [] type_env,
1252 ppr_types :: [Var] -> TypeEnv -> SDoc
1253 ppr_types dfun_ids type_env
1254 = text "TYPE SIGNATURES" $$ nest 4 (ppr_sigs ids)
1256 ids = [id | id <- typeEnvIds type_env, want_sig id]
1257 want_sig id | opt_PprStyle_Debug = True
1258 | otherwise = isLocalId id &&
1259 isExternalName (idName id) &&
1260 not (id `elem` dfun_ids)
1261 -- isLocalId ignores data constructors, records selectors etc.
1262 -- The isExternalName ignores local dictionary and method bindings
1263 -- that the type checker has invented. Top-level user-defined things
1264 -- have External names.
1266 ppr_insts :: [Var] -> SDoc
1267 ppr_insts [] = empty
1268 ppr_insts dfun_ids = text "INSTANCES" $$ nest 4 (ppr_sigs dfun_ids)
1270 ppr_sigs :: [Var] -> SDoc
1272 -- Print type signatures
1273 -- Convert to HsType so that we get source-language style printing
1274 -- And sort by RdrName
1275 = vcat $ map ppr_sig $ sortLt lt_sig $
1276 [ (getRdrName id, toHsType (tidyTopType (idType id)))
1279 lt_sig (n1,_) (n2,_) = n1 < n2
1280 ppr_sig (n,t) = ppr n <+> dcolon <+> ppr t
1283 ppr_rules :: [IdCoreRule] -> SDoc
1284 ppr_rules [] = empty
1285 ppr_rules rs = vcat [ptext SLIT("{-# RULES"),
1286 nest 4 (pprIdRules rs),
1289 ppr_gen_tycons [] = empty
1290 ppr_gen_tycons tcs = vcat [ptext SLIT("Generic type constructor details:"),
1291 nest 2 (vcat (map ppr_gen_tycon tcs))
1294 -- x&y are now Id's, not CoreExpr's
1296 | Just ep <- tyConGenInfo tycon
1297 = (ppr tycon <> colon) $$ nest 4 (ppr_ep ep)
1299 | otherwise = ppr tycon <> colon <+> ptext SLIT("Not derivable")
1302 = vcat [ ptext SLIT("Rep type:") <+> ppr (tcFunResultTy from_tau),
1303 ptext SLIT("From:") <+> ppr (unfoldingTemplate (idUnfolding from)),
1304 ptext SLIT("To:") <+> ppr (unfoldingTemplate (idUnfolding to))
1307 (_,from_tau) = tcSplitForAllTys (idType from)