/ghc-7.4.1/compiler/typecheck/TcRnDriver.lhs

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%
% (c) The University of Glasgow 2006
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[TcMovectle]{Typechecking a whole module}

\begin{code}
{-# OPTIONS -fno-warn-tabs #-}
-- The above warning supression flag is a temporary kludge.
-- While working on this module you are encouraged to remove it and
-- detab the module (please do the detabbing in a separate patch). See
--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#TabsvsSpaces
-- for details

module TcRnDriver (
#ifdef GHCI
	tcRnStmt, tcRnExpr, tcRnType,
	tcRnImportDecls,
	tcRnLookupRdrName,
	getModuleInterface,
	tcRnDeclsi,
#endif
	tcRnLookupName,
	tcRnGetInfo,
	tcRnModule, 
	tcTopSrcDecls,
	tcRnExtCore
    ) where

#ifdef GHCI
import {-# SOURCE #-} TcSplice ( tcSpliceDecls )
#endif

import DynFlags
import StaticFlags
import HsSyn
import PrelNames
import RdrName
import TcHsSyn
import TcExpr
import TcRnMonad
import TcEvidence
import Coercion( pprCoAxiom )
import FamInst
import InstEnv
import FamInstEnv
import TcAnnotations
import TcBinds
import HeaderInfo       ( mkPrelImports )
import TcType	( tidyTopType )
import TcDefaults
import TcEnv
import TcRules
import TcForeign
import TcInstDcls
import TcIface
import TcMType
import MkIface
import IfaceSyn
import TcSimplify
import TcTyClsDecls
import LoadIface
import RnNames
import RnEnv
import RnSource
import PprCore
import CoreSyn
import ErrUtils
import Id
import VarEnv
import Var
import Module
import UniqFM
import Name
import NameEnv
import NameSet
import Avail
import TyCon
import SrcLoc
import HscTypes
import ListSetOps
import Outputable
import DataCon
import Type
import Class
import TcType   ( orphNamesOfDFunHead )
import Inst	( tcGetInstEnvs )
import Data.List ( sortBy )
import Data.IORef ( readIORef )

#ifdef GHCI
import TcType   ( isUnitTy, isTauTy )
import TcHsType
import TcMatches
import RnTypes
import RnExpr
import MkId
import BasicTypes
import TidyPgm	  ( globaliseAndTidyId )
import TysWiredIn ( unitTy, mkListTy )
#endif

import FastString
import Maybes
import Util
import Bag

import Control.Monad

#include "HsVersions.h"
\end{code}

%************************************************************************
%*									*
	Typecheck and rename a module
%*									*
%************************************************************************


\begin{code}
-- | Top level entry point for typechecker and renamer
tcRnModule :: HscEnv 
	   -> HscSource
	   -> Bool 		-- True <=> save renamed syntax
           -> HsParsedModule
	   -> IO (Messages, Maybe TcGblEnv)

tcRnModule hsc_env hsc_src save_rn_syntax
   HsParsedModule {
      hpm_module =
         (L loc (HsModule maybe_mod export_ies
			  import_decls local_decls mod_deprec
                          maybe_doc_hdr)),
      hpm_src_files =
         src_files
   }
 = do { showPass (hsc_dflags hsc_env) "Renamer/typechecker" ;

   let { this_pkg = thisPackage (hsc_dflags hsc_env) ;
	 (this_mod, prel_imp_loc) 
            = case maybe_mod of
		Nothing -- 'module M where' is omitted  
                    ->  (mAIN, srcLocSpan (srcSpanStart loc))	
			    	   
		Just (L mod_loc mod)  -- The normal case
                    -> (mkModule this_pkg mod, mod_loc) } ;
		
   initTc hsc_env hsc_src save_rn_syntax this_mod $ 
   setSrcSpan loc $
   do {		-- Deal with imports; first add implicit prelude
        implicit_prelude <- xoptM Opt_ImplicitPrelude;
        let { prel_imports = mkPrelImports (moduleName this_mod) prel_imp_loc
                                         implicit_prelude import_decls } ;

        ifWOptM Opt_WarnImplicitPrelude $
             when (notNull prel_imports) $ addWarn (implicitPreludeWarn) ;

	tcg_env <- {-# SCC "tcRnImports" #-}
                   tcRnImports hsc_env this_mod (prel_imports ++ import_decls) ;
	setGblEnv tcg_env		$ do {

		-- Load the hi-boot interface for this module, if any
		-- We do this now so that the boot_names can be passed
		-- to tcTyAndClassDecls, because the boot_names are 
		-- automatically considered to be loop breakers
		--
		-- Do this *after* tcRnImports, so that we know whether
		-- a module that we import imports us; and hence whether to
		-- look for a hi-boot file
	boot_iface <- tcHiBootIface hsc_src this_mod ;

		-- Rename and type check the declarations
	traceRn (text "rn1a") ;
	tcg_env <- if isHsBoot hsc_src then
			tcRnHsBootDecls local_decls
		   else	
			{-# SCC "tcRnSrcDecls" #-}
                        tcRnSrcDecls boot_iface local_decls ;
	setGblEnv tcg_env		$ do {

		-- Report the use of any deprecated things
		-- We do this *before* processsing the export list so
		-- that we don't bleat about re-exporting a deprecated
		-- thing (especially via 'module Foo' export item)
		-- That is, only uses in the *body* of the module are complained about
	traceRn (text "rn3") ;
	failIfErrsM ;	-- finishWarnings crashes sometimes 
			-- as a result of typechecker repairs (e.g. unboundNames)
	tcg_env <- finishWarnings (hsc_dflags hsc_env) mod_deprec tcg_env ;

		-- Process the export list
        traceRn (text "rn4a: before exports");
	tcg_env <- rnExports (isJust maybe_mod) export_ies tcg_env ;
	traceRn (text "rn4b: after exportss") ;

                -- Check that main is exported (must be after rnExports)
        checkMainExported tcg_env ;

	-- Compare the hi-boot iface (if any) with the real thing
	-- Must be done after processing the exports
 	tcg_env <- checkHiBootIface tcg_env boot_iface ;

	-- The new type env is already available to stuff slurped from 
	-- interface files, via TcEnv.updateGlobalTypeEnv
	-- It's important that this includes the stuff in checkHiBootIface, 
	-- because the latter might add new bindings for boot_dfuns, 
	-- which may be mentioned in imported unfoldings

		-- Don't need to rename the Haddock documentation,
		-- it's not parsed by GHC anymore.
	tcg_env <- return (tcg_env { tcg_doc_hdr = maybe_doc_hdr }) ;

		-- Report unused names
 	reportUnusedNames export_ies tcg_env ;

                -- add extra source files to tcg_dependent_files
        addDependentFiles src_files ;

                -- Dump output and return
	tcDump tcg_env ;
	return tcg_env
    }}}}


implicitPreludeWarn :: SDoc
implicitPreludeWarn
  = ptext (sLit "Module `Prelude' implicitly imported")
\end{code}


%************************************************************************
%*									*
		Import declarations
%*									*
%************************************************************************

\begin{code}
tcRnImports :: HscEnv -> Module 
            -> [LImportDecl RdrName] -> TcM TcGblEnv
tcRnImports hsc_env this_mod import_decls
  = do	{ (rn_imports, rdr_env, imports,hpc_info) <- rnImports import_decls ;

	; let { dep_mods :: ModuleNameEnv (ModuleName, IsBootInterface)
	        -- Make sure we record the dependencies from the DynFlags in the EPS or we
	        -- end up hitting the sanity check in LoadIface.loadInterface that
	        -- checks for unknown home-package modules being loaded. We put
	        -- these dependencies on the left so their (non-source) imports
	        -- take precedence over the (possibly-source) imports on the right.
	        -- We don't add them to any other field (e.g. the imp_dep_mods of
	        -- imports) because we don't want to load their instances etc.
	      ; dep_mods = listToUFM [(mod_nm, (mod_nm, False)) | mod_nm <- dynFlagDependencies (hsc_dflags hsc_env)]
	                        `plusUFM` imp_dep_mods imports

		-- We want instance declarations from all home-package
		-- modules below this one, including boot modules, except
		-- ourselves.  The 'except ourselves' is so that we don't
		-- get the instances from this module's hs-boot file
	      ; want_instances :: ModuleName -> Bool
	      ; want_instances mod = mod `elemUFM` dep_mods
				   && mod /= moduleName this_mod
	      ; (home_insts, home_fam_insts) = hptInstances hsc_env 
                                                            want_instances
	      } ;

		-- Record boot-file info in the EPS, so that it's 
		-- visible to loadHiBootInterface in tcRnSrcDecls,
		-- and any other incrementally-performed imports
	; updateEps_ (\eps -> eps { eps_is_boot = dep_mods }) ;

		-- Update the gbl env
	; updGblEnv ( \ gbl -> 
	    gbl { 
              tcg_rdr_env      = plusOccEnv (tcg_rdr_env gbl) rdr_env,
	      tcg_imports      = tcg_imports gbl `plusImportAvails` imports,
              tcg_rn_imports   = rn_imports,
	      tcg_inst_env     = extendInstEnvList (tcg_inst_env gbl) home_insts,
	      tcg_fam_inst_env = extendFamInstEnvList (tcg_fam_inst_env gbl) 
                                                      home_fam_insts,
	      tcg_hpc          = hpc_info
	    }) $ do {

	; traceRn (text "rn1" <+> ppr (imp_dep_mods imports))
		-- Fail if there are any errors so far
		-- The error printing (if needed) takes advantage 
		-- of the tcg_env we have now set
-- 	; traceIf (text "rdr_env: " <+> ppr rdr_env)
	; failIfErrsM

		-- Load any orphan-module and family instance-module
		-- interfaces, so that their rules and instance decls will be
		-- found.
	; loadModuleInterfaces (ptext (sLit "Loading orphan modules")) 
                               (imp_orphs imports)

                -- Check type-family consistency
	; traceRn (text "rn1: checking family instance consistency")
	; let { dir_imp_mods = moduleEnvKeys
			     . imp_mods 
			     $ imports }
	; checkFamInstConsistency (imp_finsts imports) dir_imp_mods ;

	; getGblEnv } }
\end{code}


%************************************************************************
%*									*
	Type-checking external-core modules
%*									*
%************************************************************************

\begin{code}
tcRnExtCore :: HscEnv 
	    -> HsExtCore RdrName
	    -> IO (Messages, Maybe ModGuts)
	-- Nothing => some error occurred 

tcRnExtCore hsc_env (HsExtCore this_mod decls src_binds)
	-- The decls are IfaceDecls; all names are original names
 = do { showPass (hsc_dflags hsc_env) "Renamer/typechecker" ;

   initTc hsc_env ExtCoreFile False this_mod $ do {

   let { ldecls  = map noLoc decls } ;

       -- Bring the type and class decls into scope
       -- ToDo: check that this doesn't need to extract the val binds.
       --       It seems that only the type and class decls need to be in scope below because
       --          (a) tcTyAndClassDecls doesn't need the val binds, and 
       --          (b) tcExtCoreBindings doesn't need anything
       --              (in fact, it might not even need to be in the scope of
       --               this tcg_env at all)
   (tc_envs, _bndrs) <- getLocalNonValBinders emptyFsEnv {- no fixity decls -} 
                                              (mkFakeGroup ldecls) ;
   setEnvs tc_envs $ do {

   (rn_decls, _fvs) <- checkNoErrs $ rnTyClDecls [] [ldecls] ;
   -- The empty list is for extra dependencies coming from .hs-boot files
   -- See Note [Extra dependencies from .hs-boot files] in RnSource

	-- Dump trace of renaming part
   rnDump (ppr rn_decls) ;

	-- Typecheck them all together so that
	-- any mutually recursive types are done right
	-- Just discard the auxiliary bindings; they are generated 
	-- only for Haskell source code, and should already be in Core
   tcg_env   <- tcTyAndClassDecls emptyModDetails rn_decls ;
   dep_files <- liftIO $ readIORef (tcg_dependent_files tcg_env) ;

   setGblEnv tcg_env $ do {
	-- Make the new type env available to stuff slurped from interface files
   
	-- Now the core bindings
   core_binds <- initIfaceExtCore (tcExtCoreBindings src_binds) ;


	-- Wrap up
   let {
	bndrs 	   = bindersOfBinds core_binds ;
	my_exports = map (Avail . idName) bndrs ;
		-- ToDo: export the data types also?

        mod_guts = ModGuts {    mg_module    = this_mod,
                                mg_boot	     = False,
                                mg_used_names = emptyNameSet, -- ToDo: compute usage
                                mg_used_th   = False,
                                mg_dir_imps  = emptyModuleEnv, -- ??
                                mg_deps      = noDependencies,	-- ??
                                mg_exports   = my_exports,
                                mg_tcs       = tcg_tcs tcg_env,
                                mg_insts     = tcg_insts tcg_env,
                                mg_fam_insts = tcg_fam_insts tcg_env,
                                mg_inst_env  = tcg_inst_env tcg_env,
                                mg_fam_inst_env = tcg_fam_inst_env tcg_env,
                                mg_rules     = [],
                                mg_vect_decls = [],
                                mg_anns      = [],
                                mg_binds     = core_binds,

                                -- Stubs
                                mg_rdr_env   = emptyGlobalRdrEnv,
                                mg_fix_env   = emptyFixityEnv,
                                mg_warns     = NoWarnings,
                                mg_foreign   = NoStubs,
                                mg_hpc_info  = emptyHpcInfo False,
                                mg_modBreaks = emptyModBreaks,
                                mg_vect_info = noVectInfo,
                                mg_trust_pkg = False,
                                mg_dependent_files = dep_files
                            } } ;

   tcCoreDump mod_guts ;

   return mod_guts
   }}}}

mkFakeGroup :: [LTyClDecl a] -> HsGroup a
mkFakeGroup decls -- Rather clumsy; lots of unused fields
  = emptyRdrGroup { hs_tyclds = [decls] }
\end{code}


%************************************************************************
%*									*
	Type-checking the top level of a module
%*									*
%************************************************************************

\begin{code}
tcRnSrcDecls :: ModDetails -> [LHsDecl RdrName] -> TcM TcGblEnv
	-- Returns the variables free in the decls
	-- Reason: solely to report unused imports and bindings
tcRnSrcDecls boot_iface decls
 = do {   	-- Do all the declarations
	((tcg_env, tcl_env), lie) <- captureConstraints $ tc_rn_src_decls boot_iface decls ;
      ; traceTc "Tc8" empty ;
      ; setEnvs (tcg_env, tcl_env) $ 
   do { 

	     -- 	Finish simplifying class constraints
	     -- 
	     -- simplifyTop deals with constant or ambiguous InstIds.  
	     -- How could there be ambiguous ones?  They can only arise if a
	     -- top-level decl falls under the monomorphism restriction
	     -- and no subsequent decl instantiates its type.
	     --
	     -- We do this after checkMain, so that we use the type info 
	     -- that checkMain adds
	     -- 
	     -- We do it with both global and local env in scope:
	     --	 * the global env exposes the instances to simplifyTop
	     --  * the local env exposes the local Ids to simplifyTop, 
	     --    so that we get better error messages (monomorphism restriction)
	new_ev_binds <- {-# SCC "simplifyTop" #-}
                        simplifyTop lie ;
        traceTc "Tc9" empty ;

	failIfErrsM ;	-- Don't zonk if there have been errors
			-- It's a waste of time; and we may get debug warnings
			-- about strangely-typed TyCons!

        -- Zonk the final code.  This must be done last.
        -- Even simplifyTop may do some unification.
        -- This pass also warns about missing type signatures
        let { TcGblEnv { tcg_type_env  = type_env,
                         tcg_binds     = binds,
                         tcg_sigs      = sig_ns,
                         tcg_ev_binds  = cur_ev_binds,
                         tcg_imp_specs = imp_specs,
                         tcg_rules     = rules,
                         tcg_vects     = vects,
                         tcg_fords     = fords } = tcg_env
            ; all_ev_binds = cur_ev_binds `unionBags` new_ev_binds } ;

        (bind_ids, ev_binds', binds', fords', imp_specs', rules', vects') 
            <- {-# SCC "zonkTopDecls" #-}
               zonkTopDecls all_ev_binds binds sig_ns rules vects imp_specs fords ;
        
        let { final_type_env = extendTypeEnvWithIds type_env bind_ids
            ; tcg_env' = tcg_env { tcg_binds    = binds',
                                   tcg_ev_binds = ev_binds',
                                   tcg_imp_specs = imp_specs',
                                   tcg_rules    = rules', 
                                   tcg_vects    = vects', 
                                   tcg_fords    = fords' } } ;

        setGlobalTypeEnv tcg_env' final_type_env
   } }

tc_rn_src_decls :: ModDetails 
                    -> [LHsDecl RdrName] 
                    -> TcM (TcGblEnv, TcLclEnv)
-- Loops around dealing with each top level inter-splice group 
-- in turn, until it's dealt with the entire module
tc_rn_src_decls boot_details ds
 = {-# SCC "tc_rn_src_decls" #-}
   do { (first_group, group_tail) <- findSplice ds  ;
		-- If ds is [] we get ([], Nothing)
        
        -- The extra_deps are needed while renaming type and class declarations 
        -- See Note [Extra dependencies from .hs-boot files] in RnSource
	let { extra_deps = map tyConName (typeEnvTyCons (md_types boot_details)) } ;
	-- Deal with decls up to, but not including, the first splice
	(tcg_env, rn_decls) <- rnTopSrcDecls extra_deps first_group ;
		-- rnTopSrcDecls fails if there are any errors
        
	(tcg_env, tcl_env) <- setGblEnv tcg_env $ 
			      tcTopSrcDecls boot_details rn_decls ;

	-- If there is no splice, we're nearly done
	setEnvs (tcg_env, tcl_env) $ 
	case group_tail of {
	   Nothing -> do { tcg_env <- checkMain ;	-- Check for `main'
			   return (tcg_env, tcl_env) 
		      } ;

#ifndef GHCI
	-- There shouldn't be a splice
	   Just (SpliceDecl {}, _) -> do {
	failWithTc (text "Can't do a top-level splice; need a bootstrapped compiler")
#else
	-- If there's a splice, we must carry on
	   Just (SpliceDecl splice_expr _, rest_ds) -> do {

	-- Rename the splice expression, and get its supporting decls
	(rn_splice_expr, splice_fvs) <- checkNoErrs (rnLExpr splice_expr) ;
		-- checkNoErrs: don't typecheck if renaming failed
	rnDump (ppr rn_splice_expr) ;

	-- Execute the splice
	spliced_decls <- tcSpliceDecls rn_splice_expr ;

	-- Glue them on the front of the remaining decls and loop
	setGblEnv (tcg_env `addTcgDUs` usesOnly splice_fvs) $
	tc_rn_src_decls boot_details (spliced_decls ++ rest_ds)
#endif /* GHCI */
    } } }
\end{code}

%************************************************************************
%*									*
	Compiling hs-boot source files, and
	comparing the hi-boot interface with the real thing
%*									*
%************************************************************************

\begin{code}
tcRnHsBootDecls :: [LHsDecl RdrName] -> TcM TcGblEnv
tcRnHsBootDecls decls
   = do { (first_group, group_tail) <- findSplice decls

		-- Rename the declarations
        ; (tcg_env, HsGroup { 
		   hs_tyclds = tycl_decls, 
		   hs_instds = inst_decls,
		   hs_derivds = deriv_decls,
		   hs_fords  = for_decls,
		   hs_defds  = def_decls,  
		   hs_ruleds = rule_decls, 
		   hs_vects  = vect_decls, 
		   hs_annds  = _,
		   hs_valds  = val_binds }) <- rnTopSrcDecls [] first_group
        -- The empty list is for extra dependencies coming from .hs-boot files
        -- See Note [Extra dependencies from .hs-boot files] in RnSource
	; (gbl_env, lie) <- captureConstraints $ setGblEnv tcg_env $ do {


		-- Check for illegal declarations
	; case group_tail of
	     Just (SpliceDecl d _, _) -> badBootDecl "splice" d
	     Nothing                  -> return ()
	; mapM_ (badBootDecl "foreign") for_decls
	; mapM_ (badBootDecl "default") def_decls
	; mapM_ (badBootDecl "rule")    rule_decls
	; mapM_ (badBootDecl "vect")    vect_decls

		-- Typecheck type/class decls
	; traceTc "Tc2" empty
	; tcg_env <- tcTyAndClassDecls emptyModDetails tycl_decls
	; setGblEnv tcg_env    $ do {

		-- Typecheck instance decls
		-- Family instance declarations are rejected here
	; traceTc "Tc3" empty
	; (tcg_env, inst_infos, _deriv_binds) 
            <- tcInstDecls1 (concat tycl_decls) inst_decls deriv_decls

	; setGblEnv tcg_env	$ do {

		-- Typecheck value declarations
	; traceTc "Tc5" empty 
	; val_ids <- tcHsBootSigs val_binds

		-- Wrap up
		-- No simplification or zonking to do
	; traceTc "Tc7a" empty
	; gbl_env <- getGblEnv 
	
		-- Make the final type-env
		-- Include the dfun_ids so that their type sigs
		-- are written into the interface file. 
	; let { type_env0 = tcg_type_env gbl_env
	      ; type_env1 = extendTypeEnvWithIds type_env0 val_ids
	      ; type_env2 = extendTypeEnvWithIds type_env1 dfun_ids 
	      ; dfun_ids = map iDFunId inst_infos
	      }

	; setGlobalTypeEnv gbl_env type_env2
   }}}
   ; traceTc "boot" (ppr lie); return gbl_env }

badBootDecl :: String -> Located decl -> TcM ()
badBootDecl what (L loc _) 
  = addErrAt loc (char 'A' <+> text what 
      <+> ptext (sLit "declaration is not (currently) allowed in a hs-boot file"))
\end{code}

Once we've typechecked the body of the module, we want to compare what
we've found (gathered in a TypeEnv) with the hi-boot details (if any).

\begin{code}
checkHiBootIface :: TcGblEnv -> ModDetails -> TcM TcGblEnv
-- Compare the hi-boot file for this module (if there is one)
-- with the type environment we've just come up with
-- In the common case where there is no hi-boot file, the list
-- of boot_names is empty.
--
-- The bindings we return give bindings for the dfuns defined in the
-- hs-boot file, such as 	$fbEqT = $fEqT

checkHiBootIface
	tcg_env@(TcGblEnv { tcg_src = hs_src, tcg_binds = binds,
			    tcg_insts = local_insts, 
			    tcg_type_env = local_type_env, tcg_exports = local_exports })
	(ModDetails { md_insts = boot_insts, md_fam_insts = boot_fam_insts,
		      md_types = boot_type_env, md_exports = boot_exports })
  | isHsBoot hs_src	-- Current module is already a hs-boot file!
  = return tcg_env	

  | otherwise
  = do	{ traceTc "checkHiBootIface" $ vcat
             [ ppr boot_type_env, ppr boot_insts, ppr boot_exports]

		-- Check the exports of the boot module, one by one
	; mapM_ check_export boot_exports

		-- Check for no family instances
	; unless (null boot_fam_insts) $
	    panic ("TcRnDriver.checkHiBootIface: Cannot handle family " ++
		   "instances in boot files yet...")
            -- FIXME: Why?  The actual comparison is not hard, but what would
            --	      be the equivalent to the dfun bindings returned for class
            --	      instances?  We can't easily equate tycons...

		-- Check instance declarations
	; mb_dfun_prs <- mapM check_inst boot_insts
        ; let dfun_prs   = catMaybes mb_dfun_prs
              boot_dfuns = map fst dfun_prs
              dfun_binds = listToBag [ mkVarBind boot_dfun (nlHsVar dfun)
                                     | (boot_dfun, dfun) <- dfun_prs ]
              type_env'  = extendTypeEnvWithIds local_type_env boot_dfuns
              tcg_env'   = tcg_env { tcg_binds = binds `unionBags` dfun_binds }

        ; failIfErrsM
	; setGlobalTypeEnv tcg_env' type_env' }
	     -- Update the global type env *including* the knot-tied one
             -- so that if the source module reads in an interface unfolding
             -- mentioning one of the dfuns from the boot module, then it
             -- can "see" that boot dfun.   See Trac #4003
  where
    check_export boot_avail	-- boot_avail is exported by the boot iface
      | name `elem` dfun_names = return ()	
      | isWiredInName name     = return ()	-- No checking for wired-in names.  In particular,
						-- 'error' is handled by a rather gross hack
						-- (see comments in GHC.Err.hs-boot)

	-- Check that the actual module exports the same thing
      | not (null missing_names)
      = addErrAt (nameSrcSpan (head missing_names)) 
                 (missingBootThing (head missing_names) "exported by")

	-- If the boot module does not *define* the thing, we are done
	-- (it simply re-exports it, and names match, so nothing further to do)
      | isNothing mb_boot_thing = return ()

	-- Check that the actual module also defines the thing, and 
	-- then compare the definitions
      | Just real_thing <- lookupTypeEnv local_type_env name,
        Just boot_thing <- mb_boot_thing
      = when (not (checkBootDecl boot_thing real_thing))
            $ addErrAt (nameSrcSpan (getName boot_thing))
                       (let boot_decl = tyThingToIfaceDecl 
                                               (fromJust mb_boot_thing)
                            real_decl = tyThingToIfaceDecl real_thing
                        in bootMisMatch real_thing boot_decl real_decl)

      | otherwise
      = addErrTc (missingBootThing name "defined in")
      where
	name          = availName boot_avail
	mb_boot_thing = lookupTypeEnv boot_type_env name
	missing_names = case lookupNameEnv local_export_env name of
			  Nothing    -> [name]
			  Just avail -> availNames boot_avail `minusList` availNames avail
		 
    dfun_names = map getName boot_insts

    local_export_env :: NameEnv AvailInfo
    local_export_env = availsToNameEnv local_exports

    check_inst :: Instance -> TcM (Maybe (Id, Id))
	-- Returns a pair of the boot dfun in terms of the equivalent real dfun
    check_inst boot_inst
	= case [dfun | inst <- local_insts, 
		       let dfun = instanceDFunId inst,
		       idType dfun `eqType` boot_inst_ty ] of
	    [] -> do { traceTc "check_inst" (vcat [ text "local_insts" <+> vcat (map (ppr . idType . instanceDFunId) local_insts)
                                                  , text "boot_inst"   <+> ppr boot_inst
                                                  , text "boot_inst_ty" <+> ppr boot_inst_ty
                                                  ]) 
                     ; addErrTc (instMisMatch boot_inst); return Nothing }
	    (dfun:_) -> return (Just (local_boot_dfun, dfun))
	where
	  boot_dfun = instanceDFunId boot_inst
	  boot_inst_ty = idType boot_dfun
	  local_boot_dfun = Id.mkExportedLocalId (idName boot_dfun) boot_inst_ty


-- This has to compare the TyThing from the .hi-boot file to the TyThing
-- in the current source file.  We must be careful to allow alpha-renaming
-- where appropriate, and also the boot declaration is allowed to omit
-- constructors and class methods.
--
-- See rnfail055 for a good test of this stuff.

checkBootDecl :: TyThing -> TyThing -> Bool

checkBootDecl (AnId id1) (AnId id2)
  = ASSERT(id1 == id2) 
    (idType id1 `eqType` idType id2)

checkBootDecl (ATyCon tc1) (ATyCon tc2)
  = checkBootTyCon tc1 tc2

checkBootDecl (ADataCon dc1) (ADataCon _)
  = pprPanic "checkBootDecl" (ppr dc1)

checkBootDecl _ _ = False -- probably shouldn't happen

----------------
checkBootTyCon :: TyCon -> TyCon -> Bool
checkBootTyCon tc1 tc2
  | not (eqKind (tyConKind tc1) (tyConKind tc2))
  = False	-- First off, check the kind

  | Just c1 <- tyConClass_maybe tc1
  , Just c2 <- tyConClass_maybe tc2
  = let 
       (clas_tyvars1, clas_fds1, sc_theta1, _, ats1, op_stuff1) 
          = classExtraBigSig c1
       (clas_tyvars2, clas_fds2, sc_theta2, _, ats2, op_stuff2) 
          = classExtraBigSig c2

       env0 = mkRnEnv2 emptyInScopeSet
       env = rnBndrs2 env0 clas_tyvars1 clas_tyvars2

       eqSig (id1, def_meth1) (id2, def_meth2)
         = idName id1 == idName id2 &&
           eqTypeX env op_ty1 op_ty2 &&
           def_meth1 == def_meth2
         where
          (_, rho_ty1) = splitForAllTys (idType id1)
          op_ty1 = funResultTy rho_ty1
          (_, rho_ty2) = splitForAllTys (idType id2)
          op_ty2 = funResultTy rho_ty2

       eqAT (tc1, def_ats1) (tc2, def_ats2)
         = checkBootTyCon tc1 tc2 &&
           eqListBy eqATDef def_ats1 def_ats2

       -- Ignore the location of the defaults
       eqATDef (ATD tvs1 ty_pats1 ty1 _loc1) (ATD tvs2 ty_pats2 ty2 _loc2)
         = eqListBy same_kind tvs1 tvs2 &&
           eqListBy (eqTypeX env) ty_pats1 ty_pats2 &&
           eqTypeX env ty1 ty2
         where env = rnBndrs2 env0 tvs1 tvs2

       eqFD (as1,bs1) (as2,bs2) = 
         eqListBy (eqTypeX env) (mkTyVarTys as1) (mkTyVarTys as2) &&
         eqListBy (eqTypeX env) (mkTyVarTys bs1) (mkTyVarTys bs2)

       same_kind tv1 tv2 = eqKind (tyVarKind tv1) (tyVarKind tv2)
    in
       eqListBy same_kind clas_tyvars1 clas_tyvars2 &&
             -- Checks kind of class
       eqListBy eqFD clas_fds1 clas_fds2 &&
       (null sc_theta1 && null op_stuff1 && null ats1
        ||   -- Above tests for an "abstract" class
        eqListBy (eqPredX env) sc_theta1 sc_theta2 &&
        eqListBy eqSig op_stuff1 op_stuff2 &&
        eqListBy eqAT ats1 ats2) 

  | isSynTyCon tc1 && isSynTyCon tc2
  = ASSERT(tc1 == tc2)
    let tvs1 = tyConTyVars tc1; tvs2 = tyConTyVars tc2
        env = rnBndrs2 env0 tvs1 tvs2

        eqSynRhs SynFamilyTyCon SynFamilyTyCon
            = True
        eqSynRhs (SynonymTyCon t1) (SynonymTyCon t2)
            = eqTypeX env t1 t2
        eqSynRhs _ _ = False
    in
    equalLength tvs1 tvs2 &&
    eqSynRhs (synTyConRhs tc1) (synTyConRhs tc2)

  | isAlgTyCon tc1 && isAlgTyCon tc2
  = ASSERT(tc1 == tc2)
    eqKind (tyConKind tc1) (tyConKind tc2) &&
    eqListBy eqPred (tyConStupidTheta tc1) (tyConStupidTheta tc2) &&
    eqAlgRhs (algTyConRhs tc1) (algTyConRhs tc2)

  | isForeignTyCon tc1 && isForeignTyCon tc2
  = eqKind (tyConKind tc1) (tyConKind tc2) &&
    tyConExtName tc1 == tyConExtName tc2

  | otherwise = False
  where 
        env0 = mkRnEnv2 emptyInScopeSet

        eqAlgRhs (AbstractTyCon dis1) rhs2 
          | dis1      = isDistinctAlgRhs rhs2	--Check compatibility
          | otherwise = True
        eqAlgRhs DataFamilyTyCon{} DataFamilyTyCon{} = True
        eqAlgRhs tc1@DataTyCon{} tc2@DataTyCon{} =
            eqListBy eqCon (data_cons tc1) (data_cons tc2)
        eqAlgRhs tc1@NewTyCon{} tc2@NewTyCon{} =
            eqCon (data_con tc1) (data_con tc2)
        eqAlgRhs _ _ = False

        eqCon c1 c2
          =  dataConName c1 == dataConName c2
          && dataConIsInfix c1 == dataConIsInfix c2
          && dataConStrictMarks c1 == dataConStrictMarks c2
          && dataConFieldLabels c1 == dataConFieldLabels c2
          && eqType (dataConUserType c1) (dataConUserType c2)

----------------
missingBootThing :: Name -> String -> SDoc
missingBootThing name what
  = ppr name <+> ptext (sLit "is exported by the hs-boot file, but not") 
	      <+> text what <+> ptext (sLit "the module")

bootMisMatch :: TyThing -> IfaceDecl -> IfaceDecl -> SDoc
bootMisMatch thing boot_decl real_decl
  = vcat [ppr thing <+> ptext (sLit "has conflicting definitions in the module and its hs-boot file"),
	  ptext (sLit "Main module:") <+> ppr real_decl,
	  ptext (sLit "Boot file:  ") <+> ppr boot_decl]

instMisMatch :: Instance -> SDoc
instMisMatch inst
  = hang (ppr inst)
       2 (ptext (sLit "is defined in the hs-boot file, but not in the module itself"))
\end{code}


%************************************************************************
%*									*
	Type-checking the top level of a module
%*									*
%************************************************************************

tcRnGroup takes a bunch of top-level source-code declarations, and
 * renames them
 * gets supporting declarations from interface files
 * typechecks them
 * zonks them
 * and augments the TcGblEnv with the results

In Template Haskell it may be called repeatedly for each group of
declarations.  It expects there to be an incoming TcGblEnv in the
monad; it augments it and returns the new TcGblEnv.

\begin{code}
------------------------------------------------
rnTopSrcDecls :: [Name] -> HsGroup RdrName -> TcM (TcGblEnv, HsGroup Name)
-- Fails if there are any errors
rnTopSrcDecls extra_deps group
 = do { -- Rename the source decls
        traceTc "rn12" empty ;
	(tcg_env, rn_decls) <- checkNoErrs $ rnSrcDecls extra_deps group ;
        traceTc "rn13" empty ;

        -- save the renamed syntax, if we want it
	let { tcg_env'
	        | Just grp <- tcg_rn_decls tcg_env
	          = tcg_env{ tcg_rn_decls = Just (appendGroups grp rn_decls) }
	        | otherwise
	           = tcg_env };

		-- Dump trace of renaming part
	rnDump (ppr rn_decls) ;

	return (tcg_env', rn_decls)
   }

------------------------------------------------
tcTopSrcDecls :: ModDetails -> HsGroup Name -> TcM (TcGblEnv, TcLclEnv)
tcTopSrcDecls boot_details 
	(HsGroup { hs_tyclds = tycl_decls, 
		   hs_instds = inst_decls,
                   hs_derivds = deriv_decls,
		   hs_fords  = foreign_decls,
		   hs_defds  = default_decls,
		   hs_annds  = annotation_decls,
		   hs_ruleds = rule_decls,
		   hs_vects  = vect_decls,
		   hs_valds  = val_binds })
 = do {		-- Type-check the type and class decls, and all imported decls
		-- The latter come in via tycl_decls
        traceTc "Tc2" empty ;

	tcg_env <- tcTyAndClassDecls boot_details tycl_decls ;
	setGblEnv tcg_env       $ do {

		-- Source-language instances, including derivings,
		-- and import the supporting declarations
        traceTc "Tc3" empty ;
	(tcg_env, inst_infos, deriv_binds) 
            <- tcInstDecls1 (concat tycl_decls) inst_decls deriv_decls;
	setGblEnv tcg_env	$ do {

	        -- Foreign import declarations next. 
        traceTc "Tc4" empty ;
	(fi_ids, fi_decls) <- tcForeignImports foreign_decls ;
	tcExtendGlobalValEnv fi_ids	$ do {

		-- Default declarations
        traceTc "Tc4a" empty ;
	default_tys <- tcDefaults default_decls ;
	updGblEnv (\gbl -> gbl { tcg_default = default_tys }) $ do {
	
		-- Now GHC-generated derived bindings, generics, and selectors
		-- Do not generate warnings from compiler-generated code;
		-- hence the use of discardWarnings
	tc_envs <- discardWarnings (tcTopBinds deriv_binds) ;
        setEnvs tc_envs $ do {

		-- Value declarations next
        traceTc "Tc5" empty ;
	tc_envs@(tcg_env, tcl_env) <- tcTopBinds val_binds;
        setEnvs tc_envs $ do {	-- Environment doesn't change now

                -- Second pass over class and instance declarations, 
                -- now using the kind-checked decls
        traceTc "Tc6" empty ;
        inst_binds <- tcInstDecls2 (concat tycl_decls) inst_infos ;

                -- Foreign exports
        traceTc "Tc7" empty ;
        (foe_binds, foe_decls) <- tcForeignExports foreign_decls ;

                -- Annotations
        annotations <- tcAnnotations annotation_decls ;

                -- Rules
        rules <- tcRules rule_decls ;

                -- Vectorisation declarations
        vects <- tcVectDecls vect_decls ;

                -- Wrap up
        traceTc "Tc7a" empty ;
	let { all_binds = inst_binds	 `unionBags`
			  foe_binds

            ; sig_names = mkNameSet (collectHsValBinders val_binds) 
                          `minusNameSet` getTypeSigNames val_binds

                -- Extend the GblEnv with the (as yet un-zonked) 
                -- bindings, rules, foreign decls
            ; tcg_env' = tcg_env { tcg_binds = tcg_binds tcg_env `unionBags` all_binds
                                 , tcg_sigs  = tcg_sigs tcg_env `unionNameSets` sig_names
                                 , tcg_rules = tcg_rules tcg_env ++ rules
                                 , tcg_vects = tcg_vects tcg_env ++ vects
                                 , tcg_anns  = tcg_anns tcg_env ++ annotations
                                 , tcg_fords = tcg_fords tcg_env ++ foe_decls ++ fi_decls } } ;

        return (tcg_env', tcl_env)
    }}}}}}}
\end{code}


%************************************************************************
%*									*
	Checking for 'main'
%*									*
%************************************************************************

\begin{code}
checkMain :: TcM TcGblEnv
-- If we are in module Main, check that 'main' is defined.
checkMain 
  = do { tcg_env   <- getGblEnv ;
	 dflags    <- getDOpts ;
	 check_main dflags tcg_env
    }

check_main :: DynFlags -> TcGblEnv -> TcM TcGblEnv
check_main dflags tcg_env
 | mod /= main_mod
 = traceTc "checkMain not" (ppr main_mod <+> ppr mod) >>
   return tcg_env

 | otherwise
 = do	{ mb_main <- lookupGlobalOccRn_maybe main_fn
		-- Check that 'main' is in scope
		-- It might be imported from another module!
	; case mb_main of {
	     Nothing -> do { traceTc "checkMain fail" (ppr main_mod <+> ppr main_fn)
			   ; complain_no_main	
			   ; return tcg_env } ;
	     Just main_name -> do

	{ traceTc "checkMain found" (ppr main_mod <+> ppr main_fn)
	; let loc = srcLocSpan (getSrcLoc main_name)
	; ioTyCon <- tcLookupTyCon ioTyConName
        ; res_ty <- newFlexiTyVarTy liftedTypeKind
	; main_expr
		<- addErrCtxt mainCtxt	  $
		   tcMonoExpr (L loc (HsVar main_name)) (mkTyConApp ioTyCon [res_ty])

		-- See Note [Root-main Id]
	   	-- Construct the binding
		-- 	:Main.main :: IO res_ty = runMainIO res_ty main 
	; run_main_id <- tcLookupId runMainIOName
	; let { root_main_name =  mkExternalName rootMainKey rOOT_MAIN 
				   (mkVarOccFS (fsLit "main")) 
				   (getSrcSpan main_name)
	      ; root_main_id = Id.mkExportedLocalId root_main_name 
						    (mkTyConApp ioTyCon [res_ty])
	      ; co  = mkWpTyApps [res_ty]
	      ; rhs = nlHsApp (mkLHsWrap co (nlHsVar run_main_id)) main_expr
	      ; main_bind = mkVarBind root_main_id rhs }

	; return (tcg_env { tcg_main  = Just main_name,
                            tcg_binds = tcg_binds tcg_env
					`snocBag` main_bind,
			    tcg_dus   = tcg_dus tcg_env
				        `plusDU` usesOnly (unitFV main_name)
			-- Record the use of 'main', so that we don't 
			-- complain about it being defined but not used
		 })
    }}}
  where
    mod 	 = tcg_mod tcg_env
    main_mod     = mainModIs dflags
    main_fn      = getMainFun dflags

    complain_no_main | ghcLink dflags == LinkInMemory = return ()
		     | otherwise = failWithTc noMainMsg
	-- In interactive mode, don't worry about the absence of 'main'
	-- In other modes, fail altogether, so that we don't go on
	-- and complain a second time when processing the export list.

    mainCtxt  = ptext (sLit "When checking the type of the") <+> pp_main_fn
    noMainMsg = ptext (sLit "The") <+> pp_main_fn
		<+> ptext (sLit "is not defined in module") <+> quotes (ppr main_mod)
    pp_main_fn = ppMainFn main_fn

ppMainFn :: RdrName -> SDoc
ppMainFn main_fn
  | main_fn == main_RDR_Unqual
  = ptext (sLit "function") <+> quotes (ppr main_fn)
  | otherwise
  = ptext (sLit "main function") <+> quotes (ppr main_fn)
	       
-- | Get the unqualified name of the function to use as the \"main\" for the main module.
-- Either returns the default name or the one configured on the command line with -main-is
getMainFun :: DynFlags -> RdrName
getMainFun dflags = case (mainFunIs dflags) of
    Just fn -> mkRdrUnqual (mkVarOccFS (mkFastString fn))
    Nothing -> main_RDR_Unqual

checkMainExported :: TcGblEnv -> TcM ()
checkMainExported tcg_env = do
  dflags    <- getDOpts
  case tcg_main tcg_env of
    Nothing -> return () -- not the main module
    Just main_name -> do
      let main_mod = mainModIs dflags
      checkTc (main_name `elem` concatMap availNames (tcg_exports tcg_env)) $
              ptext (sLit "The") <+> ppMainFn (nameRdrName main_name) <+>
              ptext (sLit "is not exported by module") <+> quotes (ppr main_mod)
\end{code}

Note [Root-main Id]
~~~~~~~~~~~~~~~~~~~
The function that the RTS invokes is always :Main.main, which we call
root_main_id.  (Because GHC allows the user to have a module not
called Main as the main module, we can't rely on the main function
being called "Main.main".  That's why root_main_id has a fixed module
":Main".)  

This is unusual: it's a LocalId whose Name has a Module from another
module.  Tiresomely, we must filter it out again in MkIface, les we
get two defns for 'main' in the interface file!


%*********************************************************
%*						 	 *
		GHCi stuff
%*							 *
%*********************************************************

\begin{code}
setInteractiveContext :: HscEnv -> InteractiveContext -> TcRn a -> TcRn a
setInteractiveContext hsc_env icxt thing_inside 
  = let -- Initialise the tcg_inst_env with instances from all home modules.  
        -- This mimics the more selective call to hptInstances in tcRnModule.
        (home_insts, home_fam_insts) = hptInstances hsc_env (\_ -> True)
        (ic_insts, ic_finsts) = ic_instances icxt

        -- Note [GHCi temporary Ids]
        -- Ideally we would just make a type_env from ic_tythings
        -- and ic_sys_vars, adding in implicit things.  However, Ids
        -- bound interactively might have some free type variables
        -- (RuntimeUnk things), and if we don't register these free
        -- TyVars as global TyVars then the typechecker will try to
        -- quantify over them and fall over in zonkQuantifiedTyVar.
        --
        -- So we must add any free TyVars to the typechecker's global
        -- TyVar set.  This is what happens when the local environment
        -- is extended, so we use tcExtendGhciEnv below which extends
        -- the local environment with the Ids.
        --
        -- However, any Ids bound this way will shadow other Ids in
        -- the GlobalRdrEnv, so we have to be careful to only add Ids
        -- which are visible in the GlobalRdrEnv.
        --
        -- Perhaps it would be better to just extend the global TyVar
        -- list from the free tyvars in the Ids here?  Anyway, at least
        -- this hack is localised.
        --
        -- Note [delete shadowed tcg_rdr_env entries]
        -- We also *delete* entries from tcg_rdr_env that we have
        -- shadowed in the local env (see above).  This isn't strictly
        -- necessary, but in an out-of-scope error when GHC suggests
        -- names it can be confusing to see multiple identical
        -- entries. (#5564)
        --
        (tmp_ids, types_n_classes) = partitionWith sel_id (ic_tythings icxt)
          where sel_id (AnId id) = Left id
                sel_id other     = Right other

        type_env = mkTypeEnvWithImplicits
                       (map AnId (ic_sys_vars icxt) ++ types_n_classes)

        visible_tmp_ids = filter visible tmp_ids
          where visible id = not (null (lookupGRE_Name (ic_rn_gbl_env icxt)
                                                       (idName id)))

        con_fields = [ (dataConName c, dataConFieldLabels c)
                     | ATyCon t <- types_n_classes
                     , c <- tyConDataCons t ]
    in
    updGblEnv (\env -> env {
          tcg_rdr_env      = delListFromOccEnv (ic_rn_gbl_env icxt)
                                               (map getOccName visible_tmp_ids)
                                 -- Note [delete shadowed tcg_rdr_env entries]
        , tcg_type_env     = type_env
        , tcg_inst_env     = extendInstEnvList
                              (extendInstEnvList (tcg_inst_env env) ic_insts)
                              home_insts
        , tcg_fam_inst_env = extendFamInstEnvList
                              (extendFamInstEnvList (tcg_fam_inst_env env)
                                                    ic_finsts)
                              home_fam_insts
        , tcg_field_env    = RecFields (mkNameEnv con_fields)
                                       (mkNameSet (concatMap snd con_fields))
             -- setting tcg_field_env is necessary to make RecordWildCards work
             -- (test: ghci049)
        }) $

        tcExtendGhciEnv visible_tmp_ids $ -- Note [GHCi temporary Ids]
          thing_inside
\end{code}


\begin{code}
#ifdef GHCI
tcRnStmt :: HscEnv
	 -> InteractiveContext
	 -> LStmt RdrName
	 -> IO (Messages, Maybe ([Id], LHsExpr Id))
		-- The returned [Id] is the list of new Ids bound by
                -- this statement.  It can be used to extend the
                -- InteractiveContext via extendInteractiveContext.
		--
		-- The returned TypecheckedHsExpr is of type IO [ () ],
		-- a list of the bound values, coerced to ().

tcRnStmt hsc_env ictxt rdr_stmt
  = initTcPrintErrors hsc_env iNTERACTIVE $ 
    setInteractiveContext hsc_env ictxt $ do {

    -- Rename; use CmdLineMode because tcRnStmt is only used interactively
    (([rn_stmt], _), fvs) <- rnStmts GhciStmt [rdr_stmt] $ \_ ->
                             return ((), emptyFVs) ;
    traceRn (text "tcRnStmt" <+> vcat [ppr rdr_stmt, ppr rn_stmt, ppr fvs]) ;
    failIfErrsM ;
    rnDump (ppr rn_stmt) ;
    
    -- The real work is done here
    (bound_ids, tc_expr) <- mkPlan rn_stmt ;
    zonked_expr <- zonkTopLExpr tc_expr ;
    zonked_ids  <- zonkTopBndrs bound_ids ;
    
	-- None of the Ids should be of unboxed type, because we
	-- cast them all to HValues in the end!
    mapM_ bad_unboxed (filter (isUnLiftedType . idType) zonked_ids) ;

    traceTc "tcs 1" empty ;
    let { global_ids = map globaliseAndTidyId zonked_ids } ;
        -- Note [Interactively-bound Ids in GHCi]

{- ---------------------------------------------
   At one stage I removed any shadowed bindings from the type_env;
   they are inaccessible but might, I suppose, cause a space leak if we leave them there.
   However, with Template Haskell they aren't necessarily inaccessible.  Consider this
   GHCi session
	 Prelude> let f n = n * 2 :: Int
	 Prelude> fName <- runQ [| f |]
	 Prelude> $(return $ AppE fName (LitE (IntegerL 7)))
	 14
	 Prelude> let f n = n * 3 :: Int
	 Prelude> $(return $ AppE fName (LitE (IntegerL 7)))
   In the last line we use 'fName', which resolves to the *first* 'f'
   in scope. If we delete it from the type env, GHCi crashes because
   it doesn't expect that.
 
   Hence this code is commented out

-------------------------------------------------- -}

    dumpOptTcRn Opt_D_dump_tc 
    	(vcat [text "Bound Ids" <+> pprWithCommas ppr global_ids,
    	       text "Typechecked expr" <+> ppr zonked_expr]) ;

    return (global_ids, zonked_expr)
    }
  where
    bad_unboxed id = addErr (sep [ptext (sLit "GHCi can't bind a variable of unlifted type:"),
				  nest 2 (ppr id <+> dcolon <+> ppr (idType id))])
\end{code}

Note [Interactively-bound Ids in GHCi]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The Ids bound by previous Stmts in GHCi are currently
	a) GlobalIds
        b) with an Internal Name (not External)
	c) and a tidied type

 (a) They must be GlobalIds (not LocalIds) otherwise when we come to
     compile an expression using these ids later, the byte code
     generator will consider the occurrences to be free rather than
     global.

 (b) They retain their Internal names becuase we don't have a suitable
     Module to name them with.  We could revisit this choice.

 (c) Their types are tidied.  This is important, because :info may ask
     to look at them, and :info expects the things it looks up to have
     tidy types
	

--------------------------------------------------------------------------
		Typechecking Stmts in GHCi

Here is the grand plan, implemented in tcUserStmt

	What you type			The IO [HValue] that hscStmt returns
	-------------			------------------------------------
	let pat = expr		==> 	let pat = expr in return [coerce HVal x, coerce HVal y, ...]
					bindings: [x,y,...]

	pat <- expr		==> 	expr >>= \ pat -> return [coerce HVal x, coerce HVal y, ...]
					bindings: [x,y,...]

	expr (of IO type)	==>	expr >>= \ it -> return [coerce HVal it]
	  [NB: result not printed]	bindings: [it]
	  
	expr (of non-IO type,	==>	let it = expr in print it >> return [coerce HVal it]
	  result showable)		bindings: [it]

	expr (of non-IO type, 
	  result not showable)	==>	error


\begin{code}
---------------------------
type PlanResult = ([Id], LHsExpr Id)
type Plan = TcM PlanResult

runPlans :: [Plan] -> TcM PlanResult
-- Try the plans in order.  If one fails (by raising an exn), try the next.
-- If one succeeds, take it.
runPlans []     = panic "runPlans"
runPlans [p]    = p
runPlans (p:ps) = tryTcLIE_ (runPlans ps) p

--------------------
mkPlan :: LStmt Name -> TcM PlanResult
mkPlan (L loc (ExprStmt expr _ _ _))	-- An expression typed at the prompt 
  = do	{ uniq <- newUnique		-- is treated very specially
        ; let fresh_it  = itName uniq loc
	      the_bind  = L loc $ mkTopFunBind (L loc fresh_it) matches
	      matches   = [mkMatch [] expr emptyLocalBinds]
	      let_stmt  = L loc $ LetStmt $ HsValBinds $
                          ValBindsOut [(NonRecursive,unitBag the_bind)] []
              bind_stmt = L loc $ BindStmt (L loc (VarPat fresh_it)) expr
					   (HsVar bindIOName) noSyntaxExpr 
	      print_it  = L loc $ ExprStmt (nlHsApp (nlHsVar printName) (nlHsVar fresh_it))
			          	   (HsVar thenIOName) noSyntaxExpr placeHolderType

	-- The plans are:
	--	[it <- e; print it]	but not if it::()
	--	[it <- e]		
	--	[let it = e; print it]	
	; runPlans [	-- Plan A
		    do { stuff@([it_id], _) <- tcGhciStmts [bind_stmt, print_it]
		       ; it_ty <- zonkTcType (idType it_id)
		       ; when (isUnitTy it_ty) failM
		       ; return stuff },

			-- Plan B; a naked bind statment
		    tcGhciStmts [bind_stmt],	

			-- Plan C; check that the let-binding is typeable all by itself.
			-- If not, fail; if so, try to print it.
			-- The two-step process avoids getting two errors: one from
			-- the expression itself, and one from the 'print it' part
			-- This two-step story is very clunky, alas
		    do { _ <- checkNoErrs (tcGhciStmts [let_stmt]) 
				--- checkNoErrs defeats the error recovery of let-bindings
		       ; tcGhciStmts [let_stmt, print_it] }
	  ]}

mkPlan stmt@(L loc (BindStmt {}))
  | [v] <- collectLStmtBinders stmt		-- One binder, for a bind stmt 
  = do	{ let print_v  = L loc $ ExprStmt (nlHsApp (nlHsVar printName) (nlHsVar v))
			          	  (HsVar thenIOName) noSyntaxExpr placeHolderType

	; print_bind_result <- doptM Opt_PrintBindResult
	; let print_plan = do
		  { stuff@([v_id], _) <- tcGhciStmts [stmt, print_v]
		  ; v_ty <- zonkTcType (idType v_id)
		  ; when (isUnitTy v_ty || not (isTauTy v_ty)) failM
		  ; return stuff }

	-- The plans are:
	--	[stmt; print v]		but not if v::()
	--	[stmt]
	; runPlans ((if print_bind_result then [print_plan] else []) ++
		    [tcGhciStmts [stmt]])
	}

mkPlan stmt…

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