\begin{code}

    -- | Handy functions for creating much Core syntax
    module MkCore (
            -- * Constructing normal syntax
            mkCoreLet, mkCoreLets,
            mkCoreApp, mkCoreApps, mkCoreConApps,
            mkCoreLams, mkWildCase, mkIfThenElse,
            mkWildValBinder, mkWildEvBinder,

            -- * Constructing boxed literals
            mkWordExpr, mkWordExprWord,
            mkIntExpr, mkIntExprInt,
            mkIntegerExpr,
            mkFloatExpr, mkDoubleExpr,
            mkCharExpr, mkStringExpr, mkStringExprFS,

            -- * Constructing general big tuples
            -- $big_tuples
            mkChunkified,

            -- * Constructing small tuples
            mkCoreVarTup, mkCoreVarTupTy, mkCoreTup,

            -- * Constructing big tuples
            mkBigCoreVarTup, mkBigCoreVarTupTy,
            mkBigCoreTup, mkBigCoreTupTy,

            -- * Deconstructing small tuples
            mkSmallTupleSelector, mkSmallTupleCase,

            -- * Deconstructing big tuples
            mkTupleSelector, mkTupleCase,

            -- * Constructing list expressions
            mkNilExpr, mkConsExpr, mkListExpr,
            mkFoldrExpr, mkBuildExpr,

        	-- * Error Ids
        	mkRuntimeErrorApp, mkImpossibleExpr, errorIds,
        	rEC_CON_ERROR_ID, iRREFUT_PAT_ERROR_ID, rUNTIME_ERROR_ID,
        	nON_EXHAUSTIVE_GUARDS_ERROR_ID, nO_METHOD_BINDING_ERROR_ID,
        	pAT_ERROR_ID, eRROR_ID, rEC_SEL_ERROR_ID, aBSENT_ERROR_ID
        ) where

    #include "HsVersions.h"

    import Id
    import IdInfo
    import Var      ( EvVar, mkWildCoVar, setTyVarUnique )

    import CoreSyn
    import CoreUtils        ( exprType, needsCaseBinding, bindNonRec )
    import Literal
    import HscTypes

    import TysWiredIn
    import PrelNames

    import TcType		( mkSigmaTy )
    import Type
    import TysPrim
    import DataCon          ( DataCon, dataConWorkId )
    import Demand
    import Name
    import Outputable
    import FastString
    import UniqSupply
    import Unique		( mkBuiltinUnique )
    import BasicTypes
    import Util             ( notNull, zipEqual )
    import Constants

    import Data.Char        ( ord )
    import Data.Word

    infixl 4 `mkCoreApp`, `mkCoreApps`

\end{code} %************************************************************************ %* * \subsection{Basic CoreSyn construction} %* * %************************************************************************ \begin{code}

    -- | Bind a binding group over an expression, using a @let@ or @case@ as
    -- appropriate (see "CoreSyn#let_app_invariant")
    mkCoreLet :: CoreBind -> CoreExpr -> CoreExpr
    mkCoreLet (NonRec bndr rhs) body        -- See Note [CoreSyn let/app invariant]
      | needsCaseBinding (idType bndr) rhs
      = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
    mkCoreLet bind body
      = Let bind body

    -- | Bind a list of binding groups over an expression. The leftmost binding
    -- group becomes the outermost group in the resulting expression
    mkCoreLets :: [CoreBind] -> CoreExpr -> CoreExpr
    mkCoreLets binds body = foldr mkCoreLet body binds

    -- | Construct an expression which represents the application of one expression
    -- to the other
    mkCoreApp :: CoreExpr -> CoreExpr -> CoreExpr
    -- Check the invariant that the arg of an App is ok-for-speculation if unlifted
    -- See CoreSyn Note [CoreSyn let/app invariant]
    mkCoreApp fun (Type ty) = App fun (Type ty)
    mkCoreApp fun arg       = ASSERT2( isFunTy fun_ty, ppr fun $$ ppr arg )
                              mk_val_app fun arg arg_ty res_ty
                          where
                            fun_ty = exprType fun
                            (arg_ty, res_ty) = splitFunTy fun_ty

    -- | Construct an expression which represents the application of a number of
    -- expressions to another. The leftmost expression in the list is applied first
    mkCoreApps :: CoreExpr -> [CoreExpr] -> CoreExpr
    -- Slightly more efficient version of (foldl mkCoreApp)
    mkCoreApps orig_fun orig_args
      = go orig_fun (exprType orig_fun) orig_args
      where
        go fun _      []               = fun
        go fun fun_ty (Type ty : args) = go (App fun (Type ty)) (applyTy fun_ty ty) args
        go fun fun_ty (arg     : args) = ASSERT2( isFunTy fun_ty, ppr fun_ty $$ ppr orig_fun $$ ppr orig_args )
                                         go (mk_val_app fun arg arg_ty res_ty) res_ty args
                                       where
                                         (arg_ty, res_ty) = splitFunTy fun_ty

    -- | Construct an expression which represents the application of a number of
    -- expressions to that of a data constructor expression. The leftmost expression
    -- in the list is applied first
    mkCoreConApps :: DataCon -> [CoreExpr] -> CoreExpr
    mkCoreConApps con args = mkCoreApps (Var (dataConWorkId con)) args

    -----------
    mk_val_app :: CoreExpr -> CoreExpr -> Type -> Type -> CoreExpr
    mk_val_app fun arg arg_ty _        -- See Note [CoreSyn let/app invariant]
      | not (needsCaseBinding arg_ty arg)
      = App fun arg                -- The vastly common case

    mk_val_app fun arg arg_ty res_ty
      = Case arg arg_id res_ty [(DEFAULT,[],App fun (Var arg_id))]
      where
        arg_id = mkWildValBinder arg_ty
    	-- Lots of shadowing, but it doesn't matter,
            -- because 'fun ' should not have a free wild-id
    	--
    	-- This is Dangerous.  But this is the only place we play this
    	-- game, mk_val_app returns an expression that does not have
    	-- have a free wild-id.  So the only thing that can go wrong
    	-- is if you take apart this case expression, and pass a
    	-- fragmet of it as the fun part of a 'mk_val_app'.

    mkWildEvBinder :: PredType -> EvVar
    mkWildEvBinder pred@(EqPred {}) = mkWildCoVar     (mkPredTy pred)
    mkWildEvBinder pred             = mkWildValBinder (mkPredTy pred)

    -- | Make a /wildcard binder/. This is typically used when you need a binder
    -- that you expect to use only at a *binding* site.  Do not use it at
    -- occurrence sites because it has a single, fixed unique, and it's very
    -- easy to get into difficulties with shadowing.  That's why it is used so little.
    mkWildValBinder :: Type -> Id
    mkWildValBinder ty = mkSysLocal (fsLit "wild") (mkBuiltinUnique 1) ty

    mkWildCase :: CoreExpr -> Type -> Type -> [CoreAlt] -> CoreExpr
    -- Make a case expression whose case binder is unused
    -- The alts should not have any occurrences of WildId
    mkWildCase scrut scrut_ty res_ty alts
      = Case scrut (mkWildValBinder scrut_ty) res_ty alts

    mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
    mkIfThenElse guard then_expr else_expr
    -- Not going to be refining, so okay to take the type of the "then" clause
      = mkWildCase guard boolTy (exprType then_expr)
    	 [ (DataAlt falseDataCon, [], else_expr),	-- Increasing order of tag!
        	   (DataAlt trueDataCon,  [], then_expr) ]

\end{code} The functions from this point don't really do anything cleverer than their counterparts in CoreSyn, but they are here for consistency \begin{code}

    -- | Create a lambda where the given expression has a number of variables
    -- bound over it. The leftmost binder is that bound by the outermost
    -- lambda in the result
    mkCoreLams :: [CoreBndr] -> CoreExpr -> CoreExpr
    mkCoreLams = mkLams

\end{code} %************************************************************************ %* * \subsection{Making literals} %* * %************************************************************************ \begin{code}

    -- | Create a 'CoreExpr' which will evaluate to the given @Int@
    mkIntExpr      :: Integer    -> CoreExpr            -- Result = I# i :: Int
    mkIntExpr  i = mkConApp intDataCon  [mkIntLit i]

    -- | Create a 'CoreExpr' which will evaluate to the given @Int@
    mkIntExprInt   :: Int        -> CoreExpr            -- Result = I# i :: Int
    mkIntExprInt  i = mkConApp intDataCon  [mkIntLitInt i]

    -- | Create a 'CoreExpr' which will evaluate to the a @Word@ with the given value
    mkWordExpr     :: Integer    -> CoreExpr
    mkWordExpr w = mkConApp wordDataCon [mkWordLit w]

    -- | Create a 'CoreExpr' which will evaluate to the given @Word@
    mkWordExprWord :: Word       -> CoreExpr
    mkWordExprWord w = mkConApp wordDataCon [mkWordLitWord w]

    -- | Create a 'CoreExpr' which will evaluate to the given @Integer@
    mkIntegerExpr  :: MonadThings m => Integer    -> m CoreExpr  -- Result :: Integer
    mkIntegerExpr i
      | inIntRange i        -- Small enough, so start from an Int
        = do integer_id <- lookupId smallIntegerName
             return (mkSmallIntegerLit integer_id i)

    -- Special case for integral literals with a large magnitude:
    -- They are transformed into an expression involving only smaller
    -- integral literals. This improves constant folding.

      | otherwise = do       -- Big, so start from a string
          plus_id <- lookupId plusIntegerName
          times_id <- lookupId timesIntegerName
          integer_id <- lookupId smallIntegerName
          let
               lit i = mkSmallIntegerLit integer_id i
               plus a b  = Var plus_id  `App` a `App` b
               times a b = Var times_id `App` a `App` b

               -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
               horner :: Integer -> Integer -> CoreExpr
               horner b i | abs q <= 1 = if r == 0 || r == i
                                         then lit i
                                         else lit r `plus` lit (i-r)
                          | r == 0     =               horner b q `times` lit b
                          | otherwise  = lit r `plus` (horner b q `times` lit b)
                          where
                            (q,r) = i `quotRem` b

          return (horner tARGET_MAX_INT i)
      where
        mkSmallIntegerLit :: Id -> Integer -> CoreExpr
        mkSmallIntegerLit small_integer i = mkApps (Var small_integer) [mkIntLit i]

    -- | Create a 'CoreExpr' which will evaluate to the given @Float@
    mkFloatExpr :: Float -> CoreExpr
    mkFloatExpr f = mkConApp floatDataCon [mkFloatLitFloat f]

    -- | Create a 'CoreExpr' which will evaluate to the given @Double@
    mkDoubleExpr :: Double -> CoreExpr
    mkDoubleExpr d = mkConApp doubleDataCon [mkDoubleLitDouble d]

    -- | Create a 'CoreExpr' which will evaluate to the given @Char@
    mkCharExpr     :: Char             -> CoreExpr      -- Result = C# c :: Int
    mkCharExpr c = mkConApp charDataCon [mkCharLit c]

    -- | Create a 'CoreExpr' which will evaluate to the given @String@
    mkStringExpr   :: MonadThings m => String     -> m CoreExpr  -- Result :: String
    -- | Create a 'CoreExpr' which will evaluate to a string morally equivalent to the given @FastString@
    mkStringExprFS :: MonadThings m => FastString -> m CoreExpr  -- Result :: String

    mkStringExpr str = mkStringExprFS (mkFastString str)

    mkStringExprFS str
      | nullFS str
      = return (mkNilExpr charTy)

      | lengthFS str == 1
      = do let the_char = mkCharExpr (headFS str)
           return (mkConsExpr charTy the_char (mkNilExpr charTy))

      | all safeChar chars
      = do unpack_id <- lookupId unpackCStringName
           return (App (Var unpack_id) (Lit (MachStr str)))

      | otherwise
      = do unpack_id <- lookupId unpackCStringUtf8Name
           return (App (Var unpack_id) (Lit (MachStr str)))

      where
        chars = unpackFS str
        safeChar c = ord c >= 1 && ord c <= 0x7F

\end{code} %************************************************************************ %* * \subsection{Tuple constructors} %* * %************************************************************************ \begin{code}

    -- $big_tuples
    -- #big_tuples#
    --
    -- GHCs built in tuples can only go up to 'mAX_TUPLE_SIZE' in arity, but
    -- we might concievably want to build such a massive tuple as part of the
    -- output of a desugaring stage (notably that for list comprehensions).
    --
    -- We call tuples above this size \"big tuples\", and emulate them by
    -- creating and pattern matching on >nested< tuples that are expressible
    -- by GHC.
    --
    -- Nesting policy: it's better to have a 2-tuple of 10-tuples (3 objects)
    -- than a 10-tuple of 2-tuples (11 objects), so we want the leaves of any
    -- construction to be big.
    --
    -- If you just use the 'mkBigCoreTup', 'mkBigCoreVarTupTy', 'mkTupleSelector'
    -- and 'mkTupleCase' functions to do all your work with tuples you should be
    -- fine, and not have to worry about the arity limitation at all.

    -- | Lifts a \"small\" constructor into a \"big\" constructor by recursive decompositon
    mkChunkified :: ([a] -> a)      -- ^ \"Small\" constructor function, of maximum input arity 'mAX_TUPLE_SIZE'
                 -> [a]             -- ^ Possible \"big\" list of things to construct from
                 -> a               -- ^ Constructed thing made possible by recursive decomposition
    mkChunkified small_tuple as = mk_big_tuple (chunkify as)
      where
    	-- Each sub-list is short enough to fit in a tuple
        mk_big_tuple [as] = small_tuple as
        mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s))

    chunkify :: [a] -> [[a]]
    -- ^ Split a list into lists that are small enough to have a corresponding
    -- tuple arity. The sub-lists of the result all have length <= 'mAX_TUPLE_SIZE'
    -- But there may be more than 'mAX_TUPLE_SIZE' sub-lists
    chunkify xs
      | n_xs <= mAX_TUPLE_SIZE = [xs]
      | otherwise		   = split xs
      where
        n_xs     = length xs
        split [] = []
        split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs)

\end{code} Creating tuples and their types for Core expressions @mkBigCoreVarTup@ builds a tuple; the inverse to @mkTupleSelector@. * If it has only one element, it is the identity function. * If there are more elements than a big tuple can have, it nests the tuples. \begin{code}

    -- | Build a small tuple holding the specified variables
    mkCoreVarTup :: [Id] -> CoreExpr
    mkCoreVarTup ids = mkCoreTup (map Var ids)

    -- | Bulid the type of a small tuple that holds the specified variables
    mkCoreVarTupTy :: [Id] -> Type
    mkCoreVarTupTy ids = mkBoxedTupleTy (map idType ids)

    -- | Build a small tuple holding the specified expressions
    mkCoreTup :: [CoreExpr] -> CoreExpr
    mkCoreTup []  = Var unitDataConId
    mkCoreTup [c] = c
    mkCoreTup cs  = mkConApp (tupleCon Boxed (length cs))
                             (map (Type . exprType) cs ++ cs)

    -- | Build a big tuple holding the specified variables
    mkBigCoreVarTup :: [Id] -> CoreExpr
    mkBigCoreVarTup ids = mkBigCoreTup (map Var ids)

    -- | Build the type of a big tuple that holds the specified variables
    mkBigCoreVarTupTy :: [Id] -> Type
    mkBigCoreVarTupTy ids = mkBigCoreTupTy (map idType ids)

    -- | Build a big tuple holding the specified expressions
    mkBigCoreTup :: [CoreExpr] -> CoreExpr
    mkBigCoreTup = mkChunkified mkCoreTup

    -- | Build the type of a big tuple that holds the specified type of thing
    mkBigCoreTupTy :: [Type] -> Type
    mkBigCoreTupTy = mkChunkified mkBoxedTupleTy

\end{code} %************************************************************************ %* * \subsection{Tuple destructors} %* * %************************************************************************ \begin{code}

    -- | Builds a selector which scrutises the given
    -- expression and extracts the one name from the list given.
    -- If you want the no-shadowing rule to apply, the caller
    -- is responsible for making sure that none of these names
    -- are in scope.
    --
    -- If there is just one 'Id' in the tuple, then the selector is
    -- just the identity.
    --
    -- If necessary, we pattern match on a \"big\" tuple.
    mkTupleSelector :: [Id]         -- ^ The 'Id's to pattern match the tuple against
                    -> Id           -- ^ The 'Id' to select
                    -> Id           -- ^ A variable of the same type as the scrutinee
                    -> CoreExpr     -- ^ Scrutinee
                    -> CoreExpr     -- ^ Selector expression

    -- mkTupleSelector [a,b,c,d] b v e
    --          = case e of v {
    --                (p,q) -> case p of p {
    --                           (a,b) -> b }}
    -- We use 'tpl' vars for the p,q, since shadowing does not matter.
    --
    -- In fact, it's more convenient to generate it innermost first, getting
    --
    --        case (case e of v
    --                (p,q) -> p) of p
    --          (a,b) -> b
    mkTupleSelector vars the_var scrut_var scrut
      = mk_tup_sel (chunkify vars) the_var
      where
        mk_tup_sel [vars] the_var = mkSmallTupleSelector vars the_var scrut_var scrut
        mk_tup_sel vars_s the_var = mkSmallTupleSelector group the_var tpl_v $
                                    mk_tup_sel (chunkify tpl_vs) tpl_v
            where
              tpl_tys = [mkBoxedTupleTy (map idType gp) | gp <- vars_s]
              tpl_vs  = mkTemplateLocals tpl_tys
              [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
                                             the_var `elem` gp ]

\end{code} \begin{code}

    -- | Like 'mkTupleSelector' but for tuples that are guaranteed
    -- never to be \"big\".
    --
    -- > mkSmallTupleSelector [x] x v e = [| e |]
    -- > mkSmallTupleSelector [x,y,z] x v e = [| case e of v { (x,y,z) -> x } |]
    mkSmallTupleSelector :: [Id]        -- The tuple args
              -> Id         -- The selected one
              -> Id         -- A variable of the same type as the scrutinee
              -> CoreExpr        -- Scrutinee
              -> CoreExpr
    mkSmallTupleSelector [var] should_be_the_same_var _ scrut
      = ASSERT(var == should_be_the_same_var)
        scrut
    mkSmallTupleSelector vars the_var scrut_var scrut
      = ASSERT( notNull vars )
        Case scrut scrut_var (idType the_var)
             [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)]

\end{code} \begin{code}

    -- | A generalization of 'mkTupleSelector', allowing the body
    -- of the case to be an arbitrary expression.
    --
    -- To avoid shadowing, we use uniques to invent new variables.
    --
    -- If necessary we pattern match on a \"big\" tuple.
    mkTupleCase :: UniqSupply       -- ^ For inventing names of intermediate variables
                -> [Id]             -- ^ The tuple identifiers to pattern match on
                -> CoreExpr         -- ^ Body of the case
                -> Id               -- ^ A variable of the same type as the scrutinee
                -> CoreExpr         -- ^ Scrutinee
                -> CoreExpr
    -- ToDo: eliminate cases where none of the variables are needed.
    --
    --         mkTupleCase uniqs [a,b,c,d] body v e
    --           = case e of v { (p,q) ->
    --             case p of p { (a,b) ->
    --             case q of q { (c,d) ->
    --             body }}}
    mkTupleCase uniqs vars body scrut_var scrut
      = mk_tuple_case uniqs (chunkify vars) body
      where
        -- This is the case where don't need any nesting
        mk_tuple_case _ [vars] body
          = mkSmallTupleCase vars body scrut_var scrut

        -- This is the case where we must make nest tuples at least once
        mk_tuple_case us vars_s body
          = let (us', vars', body') = foldr one_tuple_case (us, [], body) vars_s
                in mk_tuple_case us' (chunkify vars') body'

        one_tuple_case chunk_vars (us, vs, body)
          = let (us1, us2) = splitUniqSupply us
                scrut_var = mkSysLocal (fsLit "ds") (uniqFromSupply us1)
                  (mkBoxedTupleTy (map idType chunk_vars))
                body' = mkSmallTupleCase chunk_vars body scrut_var (Var scrut_var)
            in (us2, scrut_var:vs, body')

\end{code} \begin{code}

    -- | As 'mkTupleCase', but for a tuple that is small enough to be guaranteed
    -- not to need nesting.
    mkSmallTupleCase
            :: [Id]         -- ^ The tuple args
            -> CoreExpr     -- ^ Body of the case
            -> Id           -- ^ A variable of the same type as the scrutinee
            -> CoreExpr     -- ^ Scrutinee
            -> CoreExpr

    mkSmallTupleCase [var] body _scrut_var scrut
      = bindNonRec var scrut body
    mkSmallTupleCase vars body scrut_var scrut
    -- One branch no refinement?
      = Case scrut scrut_var (exprType body) [(DataAlt (tupleCon Boxed (length vars)), vars, body)]

\end{code} %************************************************************************ %* * \subsection{Common list manipulation expressions} %* * %************************************************************************ Call the constructor Ids when building explicit lists, so that they interact well with rules. \begin{code}

    -- | Makes a list @[]@ for lists of the specified type
    mkNilExpr :: Type -> CoreExpr
    mkNilExpr ty = mkConApp nilDataCon [Type ty]

    -- | Makes a list @(:)@ for lists of the specified type
    mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr
    mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl]

    -- | Make a list containing the given expressions, where the list has the given type
    mkListExpr :: Type -> [CoreExpr] -> CoreExpr
    mkListExpr ty xs = foldr (mkConsExpr ty) (mkNilExpr ty) xs

    -- | Make a fully applied 'foldr' expression
    mkFoldrExpr :: MonadThings m
                => Type             -- ^ Element type of the list
                -> Type             -- ^ Fold result type
                -> CoreExpr         -- ^ "Cons" function expression for the fold
                -> CoreExpr         -- ^ "Nil" expression for the fold
                -> CoreExpr         -- ^ List expression being folded acress
                -> m CoreExpr
    mkFoldrExpr elt_ty result_ty c n list = do
        foldr_id <- lookupId foldrName
        return (Var foldr_id `App` Type elt_ty
               `App` Type result_ty
               `App` c
               `App` n
               `App` list)

    -- | Make a 'build' expression applied to a locally-bound worker function
    mkBuildExpr :: (MonadThings m, MonadUnique m)
                => Type                                     -- ^ Type of list elements to be built
                -> ((Id, Type) -> (Id, Type) -> m CoreExpr) -- ^ Function that, given information about the 'Id's
                                                            -- of the binders for the build worker function, returns
                                                            -- the body of that worker
                -> m CoreExpr
    mkBuildExpr elt_ty mk_build_inside = do
        [n_tyvar] <- newTyVars [alphaTyVar]
        let n_ty = mkTyVarTy n_tyvar
            c_ty = mkFunTys [elt_ty, n_ty] n_ty
        [c, n] <- sequence [mkSysLocalM (fsLit "c") c_ty, mkSysLocalM (fsLit "n") n_ty]

        build_inside <- mk_build_inside (c, c_ty) (n, n_ty)

        build_id <- lookupId buildName
        return $ Var build_id `App` Type elt_ty `App` mkLams [n_tyvar, c, n] build_inside
      where
        newTyVars tyvar_tmpls = do
          uniqs <- getUniquesM
          return (zipWith setTyVarUnique tyvar_tmpls uniqs)

\end{code} %************************************************************************ %* * Error expressions %* * %************************************************************************ \begin{code}

    mkRuntimeErrorApp
            :: Id           -- Should be of type (forall a. Addr# -> a)
                            --      where Addr# points to a UTF8 encoded string
            -> Type         -- The type to instantiate 'a'
            -> String       -- The string to print
            -> CoreExpr

    mkRuntimeErrorApp err_id res_ty err_msg
      = mkApps (Var err_id) [Type res_ty, err_string]
      where
        err_string = Lit (mkMachString err_msg)

    mkImpossibleExpr :: Type -> CoreExpr
    mkImpossibleExpr res_ty
      = mkRuntimeErrorApp rUNTIME_ERROR_ID res_ty "Impossible case alternative"

\end{code} %************************************************************************ %* * Error Ids %* * %************************************************************************ GHC randomly injects these into the code. @patError@ is just a version of @error@ for pattern-matching failures. It knows various ``codes'' which expand to longer strings---this saves space! @absentErr@ is a thing we put in for ``absent'' arguments. They jolly well shouldn't be yanked on, but if one is, then you will get a friendly message from @absentErr@ (rather than a totally random crash). @parError@ is a special version of @error@ which the compiler does not know to be a bottoming Id. It is used in the @_par_@ and @_seq_@ templates, but we don't ever expect to generate code for it. \begin{code}

    errorIds :: [Id]
    errorIds
      = [ eRROR_ID,   -- This one isn't used anywhere else in the compiler
                      -- But we still need it in wiredInIds so that when GHC
                      -- compiles a program that mentions 'error' we don't
                      -- import its type from the interface file; we just get
                      -- the Id defined here.  Which has an 'open-tyvar' type.

          rUNTIME_ERROR_ID,
          iRREFUT_PAT_ERROR_ID,
          nON_EXHAUSTIVE_GUARDS_ERROR_ID,
          nO_METHOD_BINDING_ERROR_ID,
          pAT_ERROR_ID,
          rEC_CON_ERROR_ID,
          rEC_SEL_ERROR_ID,
          aBSENT_ERROR_ID ]

    recSelErrorName, runtimeErrorName, absentErrorName :: Name
    irrefutPatErrorName, recConErrorName, patErrorName :: Name
    nonExhaustiveGuardsErrorName, noMethodBindingErrorName :: Name

    recSelErrorName     = err_nm "recSelError"     recSelErrorIdKey     rEC_SEL_ERROR_ID
    absentErrorName     = err_nm "absentError"     absentErrorIdKey     aBSENT_ERROR_ID
    runtimeErrorName    = err_nm "runtimeError"    runtimeErrorIdKey    rUNTIME_ERROR_ID
    irrefutPatErrorName = err_nm "irrefutPatError" irrefutPatErrorIdKey iRREFUT_PAT_ERROR_ID
    recConErrorName     = err_nm "recConError"     recConErrorIdKey     rEC_CON_ERROR_ID
    patErrorName        = err_nm "patError"        patErrorIdKey        pAT_ERROR_ID

    noMethodBindingErrorName     = err_nm "noMethodBindingError"
                                      noMethodBindingErrorIdKey nO_METHOD_BINDING_ERROR_ID
    nonExhaustiveGuardsErrorName = err_nm "nonExhaustiveGuardsError"
                                      nonExhaustiveGuardsErrorIdKey nON_EXHAUSTIVE_GUARDS_ERROR_ID

    err_nm :: String -> Unique -> Id -> Name
    err_nm str uniq id = mkWiredInIdName cONTROL_EXCEPTION_BASE (fsLit str) uniq id

    rEC_SEL_ERROR_ID, rUNTIME_ERROR_ID, iRREFUT_PAT_ERROR_ID, rEC_CON_ERROR_ID :: Id
    pAT_ERROR_ID, nO_METHOD_BINDING_ERROR_ID, nON_EXHAUSTIVE_GUARDS_ERROR_ID :: Id
    rEC_SEL_ERROR_ID                = mkRuntimeErrorId recSelErrorName
    rUNTIME_ERROR_ID                = mkRuntimeErrorId runtimeErrorName
    iRREFUT_PAT_ERROR_ID            = mkRuntimeErrorId irrefutPatErrorName
    rEC_CON_ERROR_ID                = mkRuntimeErrorId recConErrorName
    pAT_ERROR_ID                    = mkRuntimeErrorId patErrorName
    nO_METHOD_BINDING_ERROR_ID      = mkRuntimeErrorId noMethodBindingErrorName
    nON_EXHAUSTIVE_GUARDS_ERROR_ID  = mkRuntimeErrorId nonExhaustiveGuardsErrorName

    aBSENT_ERROR_ID :: Id
    -- Not bottoming; no unfolding!  See Note [Absent error Id] in WwLib
    aBSENT_ERROR_ID = mkVanillaGlobal absentErrorName runtimeErrorTy

    mkRuntimeErrorId :: Name -> Id
    mkRuntimeErrorId name = pc_bottoming_Id name runtimeErrorTy

    runtimeErrorTy :: Type
    -- The runtime error Ids take a UTF8-encoded string as argument
    runtimeErrorTy = mkSigmaTy [openAlphaTyVar] [] (mkFunTy addrPrimTy openAlphaTy)

\end{code} \begin{code}

    errorName :: Name
    errorName = mkWiredInIdName gHC_ERR (fsLit "error") errorIdKey eRROR_ID

    eRROR_ID :: Id
    eRROR_ID = pc_bottoming_Id errorName errorTy

    errorTy  :: Type
    errorTy  = mkSigmaTy [openAlphaTyVar] [] (mkFunTys [mkListTy charTy] openAlphaTy)
        -- Notice the openAlphaTyVar.  It says that "error" can be applied
        -- to unboxed as well as boxed types.  This is OK because it never
        -- returns, so the return type is irrelevant.

\end{code} %************************************************************************ %* * \subsection{Utilities} %* * %************************************************************************ \begin{code}

    pc_bottoming_Id :: Name -> Type -> Id
    -- Function of arity 1, which diverges after being given one argument
    pc_bottoming_Id name ty
     = mkVanillaGlobalWithInfo name ty bottoming_info
     where
        bottoming_info = vanillaIdInfo `setStrictnessInfo` Just strict_sig
    				   `setArityInfo`         1
    			-- Make arity and strictness agree

            -- Do *not* mark them as NoCafRefs, because they can indeed have
            -- CAF refs.  For example, pAT_ERROR_ID calls GHC.Err.untangle,
            -- which has some CAFs
            -- In due course we may arrange that these error-y things are
            -- regarded by the GC as permanently live, in which case we
            -- can give them NoCaf info.  As it is, any function that calls
            -- any pc_bottoming_Id will itself have CafRefs, which bloats
            -- SRTs.

        strict_sig = mkStrictSig (mkTopDmdType [evalDmd] BotRes)
            -- These "bottom" out, no matter what their arguments

\end{code}