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TcExpr.lhs
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TcExpr.lhs
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%
% (c) The University of Glasgow 2006
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[TcExpr]{Typecheck an expression}
\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 TcExpr ( tcPolyExpr, tcPolyExprNC, tcMonoExpr, tcMonoExprNC,
tcInferRho, tcInferRhoNC,
tcSyntaxOp, tcCheckId,
addExprErrCtxt) where
#include "HsVersions.h"
#ifdef GHCI /* Only if bootstrapped */
import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcBracket )
import qualified DsMeta
#endif
import HsSyn
import TcHsSyn
import TcRnMonad
import TcUnify
import BasicTypes
import Inst
import TcBinds
import FamInst ( tcLookupFamInst )
import FamInstEnv ( famInstAxiom, dataFamInstRepTyCon, FamInstMatch(..) )
import TcEnv
import TcArrows
import TcMatches
import TcHsType
import TcPat
import TcMType
import TcType
import DsMonad hiding (Splice)
import Id
import DataCon
import RdrName
import Name
import TyCon
import Type
import TcEvidence
import Var
import VarSet
import VarEnv
import TysWiredIn
import TysPrim( intPrimTy )
import PrimOp( tagToEnumKey )
import PrelNames
import DynFlags
import SrcLoc
import Util
import ListSetOps
import Maybes
import ErrUtils
import Outputable
import FastString
import Control.Monad
import Class(classTyCon)
\end{code}
%************************************************************************
%* *
\subsection{Main wrappers}
%* *
%************************************************************************
\begin{code}
tcPolyExpr, tcPolyExprNC
:: LHsExpr Name -- Expression to type check
-> TcSigmaType -- Expected type (could be a polytpye)
-> TcM (LHsExpr TcId) -- Generalised expr with expected type
-- tcPolyExpr is a convenient place (frequent but not too frequent)
-- place to add context information.
-- The NC version does not do so, usually because the caller wants
-- to do so himself.
tcPolyExpr expr res_ty
= addExprErrCtxt expr $
do { traceTc "tcPolyExpr" (ppr res_ty); tcPolyExprNC expr res_ty }
tcPolyExprNC expr res_ty
= do { traceTc "tcPolyExprNC" (ppr res_ty)
; (gen_fn, expr') <- tcGen GenSigCtxt res_ty $ \ _ rho ->
tcMonoExprNC expr rho
; return (mkLHsWrap gen_fn expr') }
---------------
tcMonoExpr, tcMonoExprNC
:: LHsExpr Name -- Expression to type check
-> TcRhoType -- Expected type (could be a type variable)
-- Definitely no foralls at the top
-> TcM (LHsExpr TcId)
tcMonoExpr expr res_ty
= addErrCtxt (exprCtxt expr) $
tcMonoExprNC expr res_ty
tcMonoExprNC (L loc expr) res_ty
= ASSERT( not (isSigmaTy res_ty) )
setSrcSpan loc $
do { expr' <- tcExpr expr res_ty
; return (L loc expr') }
---------------
tcInferRho, tcInferRhoNC :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
-- Infer a *rho*-type. This is, in effect, a special case
-- for ids and partial applications, so that if
-- f :: Int -> (forall a. a -> a) -> Int
-- then we can infer
-- f 3 :: (forall a. a -> a) -> Int
-- And that in turn is useful
-- (a) for the function part of any application (see tcApp)
-- (b) for the special rule for '$'
tcInferRho expr = addErrCtxt (exprCtxt expr) (tcInferRhoNC expr)
tcInferRhoNC (L loc expr)
= setSrcSpan loc $
do { (expr', rho) <- tcInfExpr expr
; return (L loc expr', rho) }
tcInfExpr :: HsExpr Name -> TcM (HsExpr TcId, TcRhoType)
tcInfExpr (HsVar f) = tcInferId f
tcInfExpr (HsPar e) = do { (e', ty) <- tcInferRhoNC e
; return (HsPar e', ty) }
tcInfExpr (HsApp e1 e2) = tcInferApp e1 [e2]
tcInfExpr e = tcInfer (tcExpr e)
tcHole :: OccName -> TcRhoType -> TcM (HsExpr TcId)
tcHole occ res_ty
= do { ty <- newFlexiTyVarTy liftedTypeKind
; name <- newSysName occ
; let ev = mkLocalId name ty
; loc <- getCtLoc HoleOrigin
; let can = CHoleCan { cc_ev = CtWanted ty ev, cc_loc = loc, cc_occ = occ }
; emitInsoluble can
; tcWrapResult (HsVar ev) ty res_ty }
\end{code}
%************************************************************************
%* *
tcExpr: the main expression typechecker
%* *
%************************************************************************
\begin{code}
tcExpr :: HsExpr Name -> TcRhoType -> TcM (HsExpr TcId)
tcExpr e res_ty | debugIsOn && isSigmaTy res_ty -- Sanity check
= pprPanic "tcExpr: sigma" (ppr res_ty $$ ppr e)
tcExpr (HsVar name) res_ty = tcCheckId name res_ty
tcExpr (HsApp e1 e2) res_ty = tcApp e1 [e2] res_ty
tcExpr (HsLit lit) res_ty = do { let lit_ty = hsLitType lit
; tcWrapResult (HsLit lit) lit_ty res_ty }
tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExprNC expr res_ty
; return (HsPar expr') }
tcExpr (HsSCC lbl expr) res_ty
= do { expr' <- tcMonoExpr expr res_ty
; return (HsSCC lbl expr') }
tcExpr (HsTickPragma info expr) res_ty
= do { expr' <- tcMonoExpr expr res_ty
; return (HsTickPragma info expr') }
tcExpr (HsCoreAnn lbl expr) res_ty
= do { expr' <- tcMonoExpr expr res_ty
; return (HsCoreAnn lbl expr') }
tcExpr (HsOverLit lit) res_ty
= do { lit' <- newOverloadedLit (LiteralOrigin lit) lit res_ty
; return (HsOverLit lit') }
tcExpr (NegApp expr neg_expr) res_ty
= do { neg_expr' <- tcSyntaxOp NegateOrigin neg_expr
(mkFunTy res_ty res_ty)
; expr' <- tcMonoExpr expr res_ty
; return (NegApp expr' neg_expr') }
tcExpr (HsIPVar x) res_ty
= do { let origin = IPOccOrigin x
; ipClass <- tcLookupClass ipClassName
{- Implicit parameters must have a *tau-type* not a.
type scheme. We enforce this by creating a fresh
type variable as its type. (Because res_ty may not
be a tau-type.) -}
; ip_ty <- newFlexiTyVarTy openTypeKind
; let ip_name = mkStrLitTy (hsIPNameFS x)
; ip_var <- emitWanted origin (mkClassPred ipClass [ip_name, ip_ty])
; tcWrapResult (fromDict ipClass ip_name ip_ty (HsVar ip_var)) ip_ty res_ty }
where
-- Coerces a dictionry for `IP "x" t` into `t`.
fromDict ipClass x ty =
case unwrapNewTyCon_maybe (classTyCon ipClass) of
Just (_,_,ax) -> HsWrap $ WpCast $ mkTcUnbranchedAxInstCo ax [x,ty]
Nothing -> panic "The dictionary for `IP` is not a newtype?"
tcExpr (HsLam match) res_ty
= do { (co_fn, match') <- tcMatchLambda match res_ty
; return (mkHsWrap co_fn (HsLam match')) }
tcExpr e@(HsLamCase _ matches) res_ty
= do { (co_fn, [arg_ty], body_ty) <- matchExpectedFunTys msg 1 res_ty
; matches' <- tcMatchesCase match_ctxt arg_ty matches body_ty
; return $ mkHsWrapCo co_fn $ HsLamCase arg_ty matches' }
where msg = sep [ ptext (sLit "The function") <+> quotes (ppr e)
, ptext (sLit "requires")]
match_ctxt = MC { mc_what = CaseAlt, mc_body = tcBody }
tcExpr (ExprWithTySig expr sig_ty) res_ty
= do { sig_tc_ty <- tcHsSigType ExprSigCtxt sig_ty
-- Remember to extend the lexical type-variable environment
; (gen_fn, expr')
<- tcGen ExprSigCtxt sig_tc_ty $ \ skol_tvs res_ty ->
tcExtendTyVarEnv2 (hsExplicitTvs sig_ty `zip` skol_tvs) $
-- See Note [More instantiated than scoped] in TcBinds
tcMonoExprNC expr res_ty
; let inner_expr = ExprWithTySigOut (mkLHsWrap gen_fn expr') sig_ty
; (inst_wrap, rho) <- deeplyInstantiate ExprSigOrigin sig_tc_ty
; tcWrapResult (mkHsWrap inst_wrap inner_expr) rho res_ty }
tcExpr (HsType ty) _
= failWithTc (text "Can't handle type argument:" <+> ppr ty)
-- This is the syntax for type applications that I was planning
-- but there are difficulties (e.g. what order for type args)
-- so it's not enabled yet.
-- Can't eliminate it altogether from the parser, because the
-- same parser parses *patterns*.
tcExpr (HsUnboundVar v) res_ty
= tcHole (rdrNameOcc v) res_ty
\end{code}
%************************************************************************
%* *
Infix operators and sections
%* *
%************************************************************************
Note [Left sections]
~~~~~~~~~~~~~~~~~~~~
Left sections, like (4 *), are equivalent to
\ x -> (*) 4 x,
or, if PostfixOperators is enabled, just
(*) 4
With PostfixOperators we don't actually require the function to take
two arguments at all. For example, (x `not`) means (not x); you get
postfix operators! Not Haskell 98, but it's less work and kind of
useful.
Note [Typing rule for ($)]
~~~~~~~~~~~~~~~~~~~~~~~~~~
People write
runST $ blah
so much, where
runST :: (forall s. ST s a) -> a
that I have finally given in and written a special type-checking
rule just for saturated appliations of ($).
* Infer the type of the first argument
* Decompose it; should be of form (arg2_ty -> res_ty),
where arg2_ty might be a polytype
* Use arg2_ty to typecheck arg2
Note [Typing rule for seq]
~~~~~~~~~~~~~~~~~~~~~~~~~~
We want to allow
x `seq` (# p,q #)
which suggests this type for seq:
seq :: forall (a:*) (b:??). a -> b -> b,
with (b:??) meaning that be can be instantiated with an unboxed tuple.
But that's ill-kinded! Function arguments can't be unboxed tuples.
And indeed, you could not expect to do this with a partially-applied
'seq'; it's only going to work when it's fully applied. so it turns
into
case x of _ -> (# p,q #)
For a while I slid by by giving 'seq' an ill-kinded type, but then
the simplifier eta-reduced an application of seq and Lint blew up
with a kind error. It seems more uniform to treat 'seq' as it it
was a language construct.
See Note [seqId magic] in MkId, and
\begin{code}
tcExpr (OpApp arg1 op fix arg2) res_ty
| (L loc (HsVar op_name)) <- op
, op_name `hasKey` seqIdKey -- Note [Typing rule for seq]
= do { arg1_ty <- newFlexiTyVarTy liftedTypeKind
; let arg2_ty = res_ty
; arg1' <- tcArg op (arg1, arg1_ty, 1)
; arg2' <- tcArg op (arg2, arg2_ty, 2)
; op_id <- tcLookupId op_name
; let op' = L loc (HsWrap (mkWpTyApps [arg1_ty, arg2_ty]) (HsVar op_id))
; return $ OpApp arg1' op' fix arg2' }
| (L loc (HsVar op_name)) <- op
, op_name `hasKey` dollarIdKey -- Note [Typing rule for ($)]
= do { traceTc "Application rule" (ppr op)
; (arg1', arg1_ty) <- tcInferRho arg1
; let doc = ptext (sLit "The first argument of ($) takes")
; (co_arg1, [arg2_ty], op_res_ty) <- matchExpectedFunTys doc 1 arg1_ty
-- arg1_ty = arg2_ty -> op_res_ty
-- And arg2_ty maybe polymorphic; that's the point
-- Make sure that the argument and result types have kind '*'
-- Eg we do not want to allow (D# $ 4.0#) Trac #5570
-- (which gives a seg fault)
-- We do this by unifying with a MetaTv; but of course
-- it must allow foralls in the type it unifies with (hence PolyTv)!
-- ($) :: forall ab. (a->b) -> a -> b
; a_ty <- newPolyFlexiTyVarTy
; b_ty <- newPolyFlexiTyVarTy
; arg2' <- tcArg op (arg2, arg2_ty, 2)
; co_res <- unifyType b_ty res_ty -- b ~ res
; co_a <- unifyType arg2_ty a_ty -- arg2 ~ a
; co_b <- unifyType op_res_ty b_ty -- op_res ~ b
; op_id <- tcLookupId op_name
; let op' = L loc (HsWrap (mkWpTyApps [a_ty, b_ty]) (HsVar op_id))
; return $ mkHsWrapCo (co_res) $
OpApp (mkLHsWrapCo (mkTcFunCo co_a co_b) $
mkLHsWrapCo co_arg1 arg1')
op' fix
(mkLHsWrapCo co_a arg2') }
| otherwise
= do { traceTc "Non Application rule" (ppr op)
; (op', op_ty) <- tcInferFun op
; (co_fn, arg_tys, op_res_ty) <- unifyOpFunTysWrap op 2 op_ty
; co_res <- unifyType op_res_ty res_ty
; [arg1', arg2'] <- tcArgs op [arg1, arg2] arg_tys
; return $ mkHsWrapCo co_res $
OpApp arg1' (mkLHsWrapCo co_fn op') fix arg2' }
-- Right sections, equivalent to \ x -> x `op` expr, or
-- \ x -> op x expr
tcExpr (SectionR op arg2) res_ty
= do { (op', op_ty) <- tcInferFun op
; (co_fn, [arg1_ty, arg2_ty], op_res_ty) <- unifyOpFunTysWrap op 2 op_ty
; co_res <- unifyType (mkFunTy arg1_ty op_res_ty) res_ty
; arg2' <- tcArg op (arg2, arg2_ty, 2)
; return $ mkHsWrapCo co_res $
SectionR (mkLHsWrapCo co_fn op') arg2' }
tcExpr (SectionL arg1 op) res_ty
= do { (op', op_ty) <- tcInferFun op
; dflags <- getDynFlags -- Note [Left sections]
; let n_reqd_args | xopt Opt_PostfixOperators dflags = 1
| otherwise = 2
; (co_fn, (arg1_ty:arg_tys), op_res_ty) <- unifyOpFunTysWrap op n_reqd_args op_ty
; co_res <- unifyType (mkFunTys arg_tys op_res_ty) res_ty
; arg1' <- tcArg op (arg1, arg1_ty, 1)
; return $ mkHsWrapCo co_res $
SectionL arg1' (mkLHsWrapCo co_fn op') }
tcExpr (ExplicitTuple tup_args boxity) res_ty
| all tupArgPresent tup_args
= do { let tup_tc = tupleTyCon (boxityNormalTupleSort boxity) (length tup_args)
; (coi, arg_tys) <- matchExpectedTyConApp tup_tc res_ty
; tup_args1 <- tcTupArgs tup_args arg_tys
; return $ mkHsWrapCo coi (ExplicitTuple tup_args1 boxity) }
| otherwise
= -- The tup_args are a mixture of Present and Missing (for tuple sections)
do { let kind = case boxity of { Boxed -> liftedTypeKind
; Unboxed -> openTypeKind }
arity = length tup_args
tup_tc = tupleTyCon (boxityNormalTupleSort boxity) arity
; arg_tys <- newFlexiTyVarTys (tyConArity tup_tc) kind
; let actual_res_ty
= mkFunTys [ty | (ty, Missing _) <- arg_tys `zip` tup_args]
(mkTyConApp tup_tc arg_tys)
; coi <- unifyType actual_res_ty res_ty
-- Handle tuple sections where
; tup_args1 <- tcTupArgs tup_args arg_tys
; return $ mkHsWrapCo coi (ExplicitTuple tup_args1 boxity) }
tcExpr (ExplicitList _ witness exprs) res_ty
= case witness of
Nothing -> do { (coi, elt_ty) <- matchExpectedListTy res_ty
; exprs' <- mapM (tc_elt elt_ty) exprs
; return $ mkHsWrapCo coi (ExplicitList elt_ty Nothing exprs') }
Just fln -> do { list_ty <- newFlexiTyVarTy liftedTypeKind
; fln' <- tcSyntaxOp ListOrigin fln (mkFunTys [intTy, list_ty] res_ty)
; (coi, elt_ty) <- matchExpectedListTy list_ty
; exprs' <- mapM (tc_elt elt_ty) exprs
; return $ mkHsWrapCo coi (ExplicitList elt_ty (Just fln') exprs') }
where tc_elt elt_ty expr = tcPolyExpr expr elt_ty
tcExpr (ExplicitPArr _ exprs) res_ty -- maybe empty
= do { (coi, elt_ty) <- matchExpectedPArrTy res_ty
; exprs' <- mapM (tc_elt elt_ty) exprs
; return $ mkHsWrapCo coi (ExplicitPArr elt_ty exprs') }
where
tc_elt elt_ty expr = tcPolyExpr expr elt_ty
\end{code}
%************************************************************************
%* *
Let, case, if, do
%* *
%************************************************************************
\begin{code}
tcExpr (HsLet binds expr) res_ty
= do { (binds', expr') <- tcLocalBinds binds $
tcMonoExpr expr res_ty
; return (HsLet binds' expr') }
tcExpr (HsCase scrut matches) exp_ty
= do { -- We used to typecheck the case alternatives first.
-- The case patterns tend to give good type info to use
-- when typechecking the scrutinee. For example
-- case (map f) of
-- (x:xs) -> ...
-- will report that map is applied to too few arguments
--
-- But now, in the GADT world, we need to typecheck the scrutinee
-- first, to get type info that may be refined in the case alternatives
(scrut', scrut_ty) <- tcInferRho scrut
; traceTc "HsCase" (ppr scrut_ty)
; matches' <- tcMatchesCase match_ctxt scrut_ty matches exp_ty
; return (HsCase scrut' matches') }
where
match_ctxt = MC { mc_what = CaseAlt,
mc_body = tcBody }
tcExpr (HsIf Nothing pred b1 b2) res_ty -- Ordinary 'if'
= do { pred' <- tcMonoExpr pred boolTy
; b1' <- tcMonoExpr b1 res_ty
; b2' <- tcMonoExpr b2 res_ty
; return (HsIf Nothing pred' b1' b2') }
tcExpr (HsIf (Just fun) pred b1 b2) res_ty -- Note [Rebindable syntax for if]
= do { pred_ty <- newFlexiTyVarTy openTypeKind
; b1_ty <- newFlexiTyVarTy openTypeKind
; b2_ty <- newFlexiTyVarTy openTypeKind
; let if_ty = mkFunTys [pred_ty, b1_ty, b2_ty] res_ty
; fun' <- tcSyntaxOp IfOrigin fun if_ty
; pred' <- tcMonoExpr pred pred_ty
; b1' <- tcMonoExpr b1 b1_ty
; b2' <- tcMonoExpr b2 b2_ty
-- Fundamentally we are just typing (ifThenElse e1 e2 e3)
-- so maybe we should use the code for function applications
-- (which would allow ifThenElse to be higher rank).
-- But it's a little awkward, so I'm leaving it alone for now
-- and it maintains uniformity with other rebindable syntax
; return (HsIf (Just fun') pred' b1' b2') }
tcExpr (HsMultiIf _ alts) res_ty
= do { alts' <- mapM (wrapLocM $ tcGRHS match_ctxt res_ty) alts
; return $ HsMultiIf res_ty alts' }
where match_ctxt = MC { mc_what = IfAlt, mc_body = tcBody }
tcExpr (HsDo do_or_lc stmts _) res_ty
= tcDoStmts do_or_lc stmts res_ty
tcExpr (HsProc pat cmd) res_ty
= do { (pat', cmd', coi) <- tcProc pat cmd res_ty
; return $ mkHsWrapCo coi (HsProc pat' cmd') }
\end{code}
Note [Rebindable syntax for if]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The rebindable syntax for 'if' uses the most flexible possible type
for conditionals:
ifThenElse :: p -> b1 -> b2 -> res
to support expressions like this:
ifThenElse :: Maybe a -> (a -> b) -> b -> b
ifThenElse (Just a) f _ = f a ifThenElse Nothing _ e = e
example :: String
example = if Just 2
then \v -> show v
else "No value"
%************************************************************************
%* *
Record construction and update
%* *
%************************************************************************
\begin{code}
tcExpr (RecordCon (L loc con_name) _ rbinds) res_ty
= do { data_con <- tcLookupDataCon con_name
-- Check for missing fields
; checkMissingFields data_con rbinds
; (con_expr, con_tau) <- tcInferId con_name
; let arity = dataConSourceArity data_con
(arg_tys, actual_res_ty) = tcSplitFunTysN con_tau arity
con_id = dataConWrapId data_con
; co_res <- unifyType actual_res_ty res_ty
; rbinds' <- tcRecordBinds data_con arg_tys rbinds
; return $ mkHsWrapCo co_res $
RecordCon (L loc con_id) con_expr rbinds' }
\end{code}
Note [Type of a record update]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The main complication with RecordUpd is that we need to explicitly
handle the *non-updated* fields. Consider:
data T a b c = MkT1 { fa :: a, fb :: (b,c) }
| MkT2 { fa :: a, fb :: (b,c), fc :: c -> c }
| MkT3 { fd :: a }
upd :: T a b c -> (b',c) -> T a b' c
upd t x = t { fb = x}
The result type should be (T a b' c)
not (T a b c), because 'b' *is not* mentioned in a non-updated field
not (T a b' c'), because 'c' *is* mentioned in a non-updated field
NB that it's not good enough to look at just one constructor; we must
look at them all; cf Trac #3219
After all, upd should be equivalent to:
upd t x = case t of
MkT1 p q -> MkT1 p x
MkT2 a b -> MkT2 p b
MkT3 d -> error ...
So we need to give a completely fresh type to the result record,
and then constrain it by the fields that are *not* updated ("p" above).
We call these the "fixed" type variables, and compute them in getFixedTyVars.
Note that because MkT3 doesn't contain all the fields being updated,
its RHS is simply an error, so it doesn't impose any type constraints.
Hence the use of 'relevant_cont'.
Note [Implict type sharing]
~~~~~~~~~~~~~~~~~~~~~~~~~~~
We also take into account any "implicit" non-update fields. For example
data T a b where { MkT { f::a } :: T a a; ... }
So the "real" type of MkT is: forall ab. (a~b) => a -> T a b
Then consider
upd t x = t { f=x }
We infer the type
upd :: T a b -> a -> T a b
upd (t::T a b) (x::a)
= case t of { MkT (co:a~b) (_:a) -> MkT co x }
We can't give it the more general type
upd :: T a b -> c -> T c b
Note [Criteria for update]
~~~~~~~~~~~~~~~~~~~~~~~~~~
We want to allow update for existentials etc, provided the updated
field isn't part of the existential. For example, this should be ok.
data T a where { MkT { f1::a, f2::b->b } :: T a }
f :: T a -> b -> T b
f t b = t { f1=b }
The criterion we use is this:
The types of the updated fields
mention only the universally-quantified type variables
of the data constructor
NB: this is not (quite) the same as being a "naughty" record selector
(See Note [Naughty record selectors]) in TcTyClsDecls), at least
in the case of GADTs. Consider
data T a where { MkT :: { f :: a } :: T [a] }
Then f is not "naughty" because it has a well-typed record selector.
But we don't allow updates for 'f'. (One could consider trying to
allow this, but it makes my head hurt. Badly. And no one has asked
for it.)
In principle one could go further, and allow
g :: T a -> T a
g t = t { f2 = \x -> x }
because the expression is polymorphic...but that seems a bridge too far.
Note [Data family example]
~~~~~~~~~~~~~~~~~~~~~~~~~~
data instance T (a,b) = MkT { x::a, y::b }
--->
data :TP a b = MkT { a::a, y::b }
coTP a b :: T (a,b) ~ :TP a b
Suppose r :: T (t1,t2), e :: t3
Then r { x=e } :: T (t3,t1)
--->
case r |> co1 of
MkT x y -> MkT e y |> co2
where co1 :: T (t1,t2) ~ :TP t1 t2
co2 :: :TP t3 t2 ~ T (t3,t2)
The wrapping with co2 is done by the constructor wrapper for MkT
Outgoing invariants
~~~~~~~~~~~~~~~~~~~
In the outgoing (HsRecordUpd scrut binds cons in_inst_tys out_inst_tys):
* cons are the data constructors to be updated
* in_inst_tys, out_inst_tys have same length, and instantiate the
*representation* tycon of the data cons. In Note [Data
family example], in_inst_tys = [t1,t2], out_inst_tys = [t3,t2]
\begin{code}
tcExpr (RecordUpd record_expr rbinds _ _ _) res_ty
= ASSERT( notNull upd_fld_names )
do {
-- STEP 0
-- Check that the field names are really field names
; sel_ids <- mapM tcLookupField upd_fld_names
-- The renamer has already checked that
-- selectors are all in scope
; let bad_guys = [ setSrcSpan loc $ addErrTc (notSelector fld_name)
| (fld, sel_id) <- rec_flds rbinds `zip` sel_ids,
not (isRecordSelector sel_id), -- Excludes class ops
let L loc fld_name = hsRecFieldId fld ]
; unless (null bad_guys) (sequence bad_guys >> failM)
-- STEP 1
-- Figure out the tycon and data cons from the first field name
; let -- It's OK to use the non-tc splitters here (for a selector)
sel_id : _ = sel_ids
(tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
data_cons = tyConDataCons tycon -- it's not a field label
-- NB: for a data type family, the tycon is the instance tycon
relevant_cons = filter is_relevant data_cons
is_relevant con = all (`elem` dataConFieldLabels con) upd_fld_names
-- A constructor is only relevant to this process if
-- it contains *all* the fields that are being updated
-- Other ones will cause a runtime error if they occur
-- Take apart a representative constructor
con1 = ASSERT( not (null relevant_cons) ) head relevant_cons
(con1_tvs, _, _, _, con1_arg_tys, _) = dataConFullSig con1
con1_flds = dataConFieldLabels con1
con1_res_ty = mkFamilyTyConApp tycon (mkTyVarTys con1_tvs)
-- Step 2
-- Check that at least one constructor has all the named fields
-- i.e. has an empty set of bad fields returned by badFields
; checkTc (not (null relevant_cons)) (badFieldsUpd rbinds)
-- STEP 3 Note [Criteria for update]
-- Check that each updated field is polymorphic; that is, its type
-- mentions only the universally-quantified variables of the data con
; let flds1_w_tys = zipEqual "tcExpr:RecConUpd" con1_flds con1_arg_tys
upd_flds1_w_tys = filter is_updated flds1_w_tys
is_updated (fld,_) = fld `elem` upd_fld_names
bad_upd_flds = filter bad_fld upd_flds1_w_tys
con1_tv_set = mkVarSet con1_tvs
bad_fld (fld, ty) = fld `elem` upd_fld_names &&
not (tyVarsOfType ty `subVarSet` con1_tv_set)
; checkTc (null bad_upd_flds) (badFieldTypes bad_upd_flds)
-- STEP 4 Note [Type of a record update]
-- Figure out types for the scrutinee and result
-- Both are of form (T a b c), with fresh type variables, but with
-- common variables where the scrutinee and result must have the same type
-- These are variables that appear in *any* arg of *any* of the
-- relevant constructors *except* in the updated fields
--
; let fixed_tvs = getFixedTyVars con1_tvs relevant_cons
is_fixed_tv tv = tv `elemVarSet` fixed_tvs
mk_inst_ty :: TvSubst -> (TKVar, TcType) -> TcM (TvSubst, TcType)
-- Deals with instantiation of kind variables
-- c.f. TcMType.tcInstTyVarsX
mk_inst_ty subst (tv, result_inst_ty)
| is_fixed_tv tv -- Same as result type
= return (extendTvSubst subst tv result_inst_ty, result_inst_ty)
| otherwise -- Fresh type, of correct kind
= do { new_ty <- newFlexiTyVarTy (TcType.substTy subst (tyVarKind tv))
; return (extendTvSubst subst tv new_ty, new_ty) }
; (_, result_inst_tys, result_subst) <- tcInstTyVars con1_tvs
; (scrut_subst, scrut_inst_tys) <- mapAccumLM mk_inst_ty emptyTvSubst
(con1_tvs `zip` result_inst_tys)
; let rec_res_ty = TcType.substTy result_subst con1_res_ty
scrut_ty = TcType.substTy scrut_subst con1_res_ty
con1_arg_tys' = map (TcType.substTy result_subst) con1_arg_tys
; co_res <- unifyType rec_res_ty res_ty
-- STEP 5
-- Typecheck the thing to be updated, and the bindings
; record_expr' <- tcMonoExpr record_expr scrut_ty
; rbinds' <- tcRecordBinds con1 con1_arg_tys' rbinds
-- STEP 6: Deal with the stupid theta
; let theta' = substTheta scrut_subst (dataConStupidTheta con1)
; instStupidTheta RecordUpdOrigin theta'
-- Step 7: make a cast for the scrutinee, in the case that it's from a type family
; let scrut_co | Just co_con <- tyConFamilyCoercion_maybe tycon
= WpCast (mkTcUnbranchedAxInstCo co_con scrut_inst_tys)
| otherwise
= idHsWrapper
-- Phew!
; return $ mkHsWrapCo co_res $
RecordUpd (mkLHsWrap scrut_co record_expr') rbinds'
relevant_cons scrut_inst_tys result_inst_tys }
where
upd_fld_names = hsRecFields rbinds
getFixedTyVars :: [TyVar] -> [DataCon] -> TyVarSet
-- These tyvars must not change across the updates
getFixedTyVars tvs1 cons
= mkVarSet [tv1 | con <- cons
, let (tvs, theta, arg_tys, _) = dataConSig con
flds = dataConFieldLabels con
fixed_tvs = exactTyVarsOfTypes fixed_tys
-- fixed_tys: See Note [Type of a record update]
`unionVarSet` tyVarsOfTypes theta
-- Universally-quantified tyvars that
-- appear in any of the *implicit*
-- arguments to the constructor are fixed
-- See Note [Implict type sharing]
fixed_tys = [ty | (fld,ty) <- zip flds arg_tys
, not (fld `elem` upd_fld_names)]
, (tv1,tv) <- tvs1 `zip` tvs -- Discards existentials in tvs
, tv `elemVarSet` fixed_tvs ]
\end{code}
%************************************************************************
%* *
Arithmetic sequences e.g. [a,b..]
and their parallel-array counterparts e.g. [: a,b.. :]
%* *
%************************************************************************
\begin{code}
tcExpr (ArithSeq _ witness seq) res_ty
= tcArithSeq witness seq res_ty
tcExpr (PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
= do { (coi, elt_ty) <- matchExpectedPArrTy res_ty
; expr1' <- tcPolyExpr expr1 elt_ty
; expr2' <- tcPolyExpr expr2 elt_ty
; enumFromToP <- initDsTc $ dsDPHBuiltin enumFromToPVar
; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
(idName enumFromToP) elt_ty
; return $ mkHsWrapCo coi
(PArrSeq enum_from_to (FromTo expr1' expr2')) }
tcExpr (PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
= do { (coi, elt_ty) <- matchExpectedPArrTy res_ty
; expr1' <- tcPolyExpr expr1 elt_ty
; expr2' <- tcPolyExpr expr2 elt_ty
; expr3' <- tcPolyExpr expr3 elt_ty
; enumFromThenToP <- initDsTc $ dsDPHBuiltin enumFromThenToPVar
; eft <- newMethodFromName (PArrSeqOrigin seq)
(idName enumFromThenToP) elt_ty -- !!!FIXME: chak
; return $ mkHsWrapCo coi
(PArrSeq eft (FromThenTo expr1' expr2' expr3')) }
tcExpr (PArrSeq _ _) _
= panic "TcExpr.tcExpr: Infinite parallel array!"
-- the parser shouldn't have generated it and the renamer shouldn't have
-- let it through
\end{code}
%************************************************************************
%* *
Template Haskell
%* *
%************************************************************************
\begin{code}
#ifdef GHCI /* Only if bootstrapped */
-- Rename excludes these cases otherwise
tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
tcExpr (HsBracket brack) res_ty = tcBracket brack res_ty
tcExpr e@(HsQuasiQuoteE _) _ =
pprPanic "Should never see HsQuasiQuoteE in type checker" (ppr e)
#endif /* GHCI */
\end{code}
%************************************************************************
%* *
Catch-all
%* *
%************************************************************************
\begin{code}
tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
-- Include ArrForm, ArrApp, which shouldn't appear at all
\end{code}
%************************************************************************
%* *
Arithmetic sequences [a..b] etc
%* *
%************************************************************************
\begin{code}
tcArithSeq :: Maybe (SyntaxExpr Name) -> ArithSeqInfo Name -> TcRhoType
-> TcM (HsExpr TcId)
tcArithSeq witness seq@(From expr) res_ty
= do { (coi, elt_ty, wit') <- arithSeqEltType witness res_ty
; expr' <- tcPolyExpr expr elt_ty
; enum_from <- newMethodFromName (ArithSeqOrigin seq)
enumFromName elt_ty
; return $ mkHsWrapCo coi (ArithSeq enum_from wit' (From expr')) }
tcArithSeq witness seq@(FromThen expr1 expr2) res_ty
= do { (coi, elt_ty, wit') <- arithSeqEltType witness res_ty
; expr1' <- tcPolyExpr expr1 elt_ty
; expr2' <- tcPolyExpr expr2 elt_ty
; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
enumFromThenName elt_ty
; return $ mkHsWrapCo coi (ArithSeq enum_from_then wit' (FromThen expr1' expr2')) }
tcArithSeq witness seq@(FromTo expr1 expr2) res_ty
= do { (coi, elt_ty, wit') <- arithSeqEltType witness res_ty
; expr1' <- tcPolyExpr expr1 elt_ty
; expr2' <- tcPolyExpr expr2 elt_ty
; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
enumFromToName elt_ty
; return $ mkHsWrapCo coi (ArithSeq enum_from_to wit' (FromTo expr1' expr2')) }
tcArithSeq witness seq@(FromThenTo expr1 expr2 expr3) res_ty
= do { (coi, elt_ty, wit') <- arithSeqEltType witness res_ty
; expr1' <- tcPolyExpr expr1 elt_ty
; expr2' <- tcPolyExpr expr2 elt_ty
; expr3' <- tcPolyExpr expr3 elt_ty
; eft <- newMethodFromName (ArithSeqOrigin seq)
enumFromThenToName elt_ty
; return $ mkHsWrapCo coi (ArithSeq eft wit' (FromThenTo expr1' expr2' expr3')) }
-----------------
arithSeqEltType :: Maybe (SyntaxExpr Name) -> TcRhoType
-> TcM (TcCoercion, TcType, Maybe (SyntaxExpr Id))
arithSeqEltType Nothing res_ty
= do { (coi, elt_ty) <- matchExpectedListTy res_ty
; return (coi, elt_ty, Nothing) }
arithSeqEltType (Just fl) res_ty
= do { list_ty <- newFlexiTyVarTy liftedTypeKind
; fl' <- tcSyntaxOp ListOrigin fl (mkFunTy list_ty res_ty)
; (coi, elt_ty) <- matchExpectedListTy list_ty
; return (coi, elt_ty, Just fl') }
\end{code}
%************************************************************************
%* *
Applications
%* *
%************************************************************************
\begin{code}
tcApp :: LHsExpr Name -> [LHsExpr Name] -- Function and args
-> TcRhoType -> TcM (HsExpr TcId) -- Translated fun and args
tcApp (L _ (HsPar e)) args res_ty
= tcApp e args res_ty
tcApp (L _ (HsApp e1 e2)) args res_ty
= tcApp e1 (e2:args) res_ty -- Accumulate the arguments
tcApp (L loc (HsVar fun)) args res_ty
| fun `hasKey` tagToEnumKey
, [arg] <- args
= tcTagToEnum loc fun arg res_ty
| fun `hasKey` seqIdKey
, [arg1,arg2] <- args
= tcSeq loc fun arg1 arg2 res_ty
tcApp fun args res_ty
= do { -- Type-check the function
; (fun1, fun_tau) <- tcInferFun fun
-- Extract its argument types
; (co_fun, expected_arg_tys, actual_res_ty)
<- matchExpectedFunTys (mk_app_msg fun) (length args) fun_tau
-- Typecheck the result, thereby propagating
-- info (if any) from result into the argument types
-- Both actual_res_ty and res_ty are deeply skolemised
; co_res <- addErrCtxtM (funResCtxt True (unLoc fun) actual_res_ty res_ty) $
unifyType actual_res_ty res_ty
-- Typecheck the arguments
; args1 <- tcArgs fun args expected_arg_tys
-- Assemble the result
; let fun2 = mkLHsWrapCo co_fun fun1
app = mkLHsWrapCo co_res (foldl mkHsApp fun2 args1)
; return (unLoc app) }
mk_app_msg :: LHsExpr Name -> SDoc
mk_app_msg fun = sep [ ptext (sLit "The function") <+> quotes (ppr fun)
, ptext (sLit "is applied to")]
----------------
tcInferApp :: LHsExpr Name -> [LHsExpr Name] -- Function and args
-> TcM (HsExpr TcId, TcRhoType) -- Translated fun and args
tcInferApp (L _ (HsPar e)) args = tcInferApp e args
tcInferApp (L _ (HsApp e1 e2)) args = tcInferApp e1 (e2:args)
tcInferApp fun args
= -- Very like the tcApp version, except that there is
-- no expected result type passed in
do { (fun1, fun_tau) <- tcInferFun fun
; (co_fun, expected_arg_tys, actual_res_ty)
<- matchExpectedFunTys (mk_app_msg fun) (length args) fun_tau
; args1 <- tcArgs fun args expected_arg_tys
; let fun2 = mkLHsWrapCo co_fun fun1
app = foldl mkHsApp fun2 args1
; return (unLoc app, actual_res_ty) }
----------------
tcInferFun :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
-- Infer and instantiate the type of a function
tcInferFun (L loc (HsVar name))
= do { (fun, ty) <- setSrcSpan loc (tcInferId name)
-- Don't wrap a context around a plain Id
; return (L loc fun, ty) }
tcInferFun fun
= do { (fun, fun_ty) <- tcInfer (tcMonoExpr fun)
-- Zonk the function type carefully, to expose any polymorphism
-- E.g. (( \(x::forall a. a->a). blah ) e)
-- We can see the rank-2 type of the lambda in time to genrealise e
; fun_ty' <- zonkTcType fun_ty
; (wrap, rho) <- deeplyInstantiate AppOrigin fun_ty'
; return (mkLHsWrap wrap fun, rho) }
----------------
tcArgs :: LHsExpr Name -- The function (for error messages)
-> [LHsExpr Name] -> [TcSigmaType] -- Actual arguments and expected arg types
-> TcM [LHsExpr TcId] -- Resulting args
tcArgs fun args expected_arg_tys
= mapM (tcArg fun) (zip3 args expected_arg_tys [1..])
----------------
tcArg :: LHsExpr Name -- The function (for error messages)
-> (LHsExpr Name, TcSigmaType, Int) -- Actual argument and expected arg type
-> TcM (LHsExpr TcId) -- Resulting argument
tcArg fun (arg, ty, arg_no) = addErrCtxt (funAppCtxt fun arg arg_no)
(tcPolyExprNC arg ty)
----------------
tcTupArgs :: [HsTupArg Name] -> [TcSigmaType] -> TcM [HsTupArg TcId]
tcTupArgs args tys
= ASSERT( equalLength args tys ) mapM go (args `zip` tys)
where
go (Missing {}, arg_ty) = return (Missing arg_ty)
go (Present expr, arg_ty) = do { expr' <- tcPolyExpr expr arg_ty
; return (Present expr') }
----------------
unifyOpFunTysWrap :: LHsExpr Name -> Arity -> TcRhoType
-> TcM (TcCoercion, [TcSigmaType], TcRhoType)
-- A wrapper for matchExpectedFunTys
unifyOpFunTysWrap op arity ty = matchExpectedFunTys herald arity ty
where
herald = ptext (sLit "The operator") <+> quotes (ppr op) <+> ptext (sLit "takes")