\section[TcExpr]{Typecheck an expression}
\begin{code}
-module TcExpr ( tcApp, tcExpr, tcMonoExpr, tcPolyExpr, tcId ) where
+module TcExpr ( tcExpr, tcMonoExpr, tcId ) where
#include "HsVersions.h"
HsMatchContext(..), HsDoContext(..), mkMonoBind
)
import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
-import TcHsSyn ( TcExpr, TcRecordBinds, mkHsLet )
+import TcHsSyn ( TcExpr, TcRecordBinds, simpleHsLitTy )
import TcMonad
+import TcUnify ( tcSub, tcGen, (<$>),
+ unifyTauTy, unifyFunTy, unifyListTy, unifyTupleTy
+ )
import BasicTypes ( RecFlag(..), isMarkedStrict )
import Inst ( InstOrigin(..),
LIE, mkLIE, emptyLIE, unitLIE, plusLIE, plusLIEs,
)
import TcBinds ( tcBindsAndThen )
import TcEnv ( tcLookupClass, tcLookupGlobalId, tcLookupGlobal_maybe,
- tcLookupTyCon, tcLookupDataCon, tcLookupId,
- tcExtendGlobalTyVars
+ tcLookupTyCon, tcLookupDataCon, tcLookupId
)
import TcMatches ( tcMatchesCase, tcMatchLambda, tcStmts )
-import TcMonoType ( tcHsSigType, UserTypeCtxt(..), checkSigTyVars, sigCtxt )
-import TcPat ( badFieldCon, simpleHsLitTy )
-import TcSimplify ( tcSimplifyCheck, tcSimplifyIPs )
-import TcMType ( tcInstTyVars, tcInstType,
- newTyVarTy, newTyVarTys, zonkTcType,
- unifyTauTy, unifyFunTy, unifyListTy, unifyTupleTy
- )
-import TcType ( TcType, TcTauType, tcSplitFunTys, tcSplitTyConApp,
- isQualifiedTy, mkFunTy, mkAppTy, mkTyConTy,
+import TcMonoType ( tcHsSigType, UserTypeCtxt(..) )
+import TcPat ( badFieldCon )
+import TcSimplify ( tcSimplifyIPs )
+import TcMType ( tcInstTyVars, newTyVarTy, newTyVarTys, zonkTcType )
+import TcType ( TcType, TcSigmaType, TcPhiType,
+ tcSplitFunTys, tcSplitTyConApp,
+ isSigmaTy, mkFunTy, mkAppTy, mkTyConTy,
mkTyConApp, mkClassPred, tcFunArgTy,
- isTauTy, tyVarsOfType, tyVarsOfTypes,
+ tyVarsOfTypes,
liftedTypeKind, openTypeKind, mkArrowKind,
tcSplitSigmaTy, tcTyConAppTyCon,
tidyOpenType
%************************************************************************
\begin{code}
-tcExpr :: RenamedHsExpr -- Expession to type check
- -> TcType -- Expected type (could be a polytpye)
- -> TcM (TcExpr, LIE)
+tcExpr :: RenamedHsExpr -- Expession to type check
+ -> TcSigmaType -- Expected type (could be a polytpye)
+ -> TcM (TcExpr, LIE) -- Generalised expr with expected type, and LIE
-tcExpr expr ty | isQualifiedTy ty = -- Polymorphic case
- tcPolyExpr expr ty `thenTc` \ (expr', lie, _, _, _) ->
- returnTc (expr', lie)
+tcExpr expr expected_ty
+ | not (isSigmaTy expected_ty) -- Monomorphic case
+ = tcMonoExpr expr expected_ty
- | otherwise = -- Monomorphic case
- tcMonoExpr expr ty
+ | otherwise
+ = tcGen expected_ty (tcMonoExpr expr) `thenTc` \ (gen_fn, expr', lie) ->
+ returnTc (gen_fn <$> expr', lie)
\end{code}
%************************************************************************
%* *
-\subsection{@tcPolyExpr@ typchecks an application}
+\subsection{The TAUT rules for variables}
%* *
%************************************************************************
\begin{code}
--- tcPolyExpr is like tcMonoExpr, except that the expected type
--- can be a polymorphic one.
-tcPolyExpr :: RenamedHsExpr
- -> TcType -- Expected type
- -> TcM (TcExpr, LIE, -- Generalised expr with expected type, and LIE
- TcExpr, TcTauType, LIE) -- Same thing, but instantiated; tau-type returned
-
-tcPolyExpr arg expected_arg_ty
- = -- Ha! The argument type of the function is a for-all type,
- -- An example of rank-2 polymorphism.
-
- -- To ensure that the forall'd type variables don't get unified with each
- -- other or any other types, we make fresh copy of the alleged type
- tcInstType expected_arg_ty `thenNF_Tc` \ (sig_tyvars, sig_theta, sig_tau) ->
- let
- free_tvs = tyVarsOfType expected_arg_ty
- in
- -- Type-check the arg and unify with expected type
- tcMonoExpr arg sig_tau `thenTc` \ (arg', lie_arg) ->
-
- -- Check that the sig_tyvars havn't been constrained
- -- The interesting bit here is that we must include the free variables
- -- of the expected arg ty. Here's an example:
- -- runST (newVar True)
- -- Here, if we don't make a check, we'll get a type (ST s (MutVar s Bool))
- -- for (newVar True), with s fresh. Then we unify with the runST's arg type
- -- forall s'. ST s' a. That unifies s' with s, and a with MutVar s Bool.
- -- So now s' isn't unconstrained because it's linked to a.
- -- Conclusion: include the free vars of the expected arg type in the
- -- list of "free vars" for the signature check.
-
- tcExtendGlobalTyVars free_tvs $
- tcAddErrCtxtM (sigCtxt sig_msg sig_tyvars sig_theta sig_tau) $
-
- newDicts SignatureOrigin sig_theta `thenNF_Tc` \ sig_dicts ->
- tcSimplifyCheck
- (text "the type signature of an expression")
- sig_tyvars
- sig_dicts lie_arg `thenTc` \ (free_insts, inst_binds) ->
-
- checkSigTyVars sig_tyvars free_tvs `thenTc` \ zonked_sig_tyvars ->
+tcMonoExpr :: RenamedHsExpr -- Expession to type check
+ -> TcPhiType -- Expected type (could be a type variable)
+ -- Definitely no foralls at the top
+ -- Can be a 'hole'.
+ -> TcM (TcExpr, LIE)
- let
- -- This HsLet binds any Insts which came out of the simplification.
- -- It's a bit out of place here, but using AbsBind involves inventing
- -- a couple of new names which seems worse.
- generalised_arg = TyLam zonked_sig_tyvars $
- DictLam (map instToId sig_dicts) $
- mkHsLet inst_binds $
- arg'
- in
- returnTc ( generalised_arg, free_insts,
- arg', sig_tau, lie_arg )
- where
- sig_msg = ptext SLIT("When checking an expression type signature")
+tcMonoExpr (HsVar name) res_ty
+ = tcId name `thenNF_Tc` \ (expr', lie1, id_ty) ->
+ tcSub res_ty id_ty `thenTc` \ (co_fn, lie2) ->
+ returnTc (co_fn <$> expr', lie1 `plusLIE` lie2)
+
+tcMonoExpr (HsIPVar ip) res_ty
+ = -- Implicit parameters must have a *tau-type* not a
+ -- type scheme. We enforce this by creating a fresh
+ -- type variable as its type. (Because res_ty may not
+ -- be a tau-type.)
+ newTyVarTy openTypeKind `thenNF_Tc` \ ip_ty ->
+ newIPDict (IPOcc ip) ip ip_ty `thenNF_Tc` \ (ip', inst) ->
+ tcSub res_ty ip_ty `thenTc` \ (co_fn, lie) ->
+ returnNF_Tc (co_fn <$> HsIPVar ip', lie `plusLIE` unitLIE inst)
\end{code}
+
%************************************************************************
%* *
-\subsection{The TAUT rules for variables}
+\subsection{Expressions type signatures}
%* *
%************************************************************************
\begin{code}
-tcMonoExpr :: RenamedHsExpr -- Expession to type check
- -> TcTauType -- Expected type (could be a type variable)
- -> TcM (TcExpr, LIE)
-
-tcMonoExpr (HsVar name) res_ty
- = tcId name `thenNF_Tc` \ (expr', lie, id_ty) ->
- unifyTauTy res_ty id_ty `thenTc_`
-
- -- Check that the result type doesn't have any nested for-alls.
- -- For example, a "build" on its own is no good; it must be
- -- applied to something.
- checkTc (isTauTy id_ty)
- (lurkingRank2Err name id_ty) `thenTc_`
-
- returnTc (expr', lie)
+tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
+ = tcHsSigType ExprSigCtxt poly_ty `thenTc` \ sig_tc_ty ->
+ tcAddErrCtxt (exprSigCtxt in_expr) $
+ tcExpr expr sig_tc_ty `thenTc` \ (expr', lie1) ->
+ tcSub res_ty sig_tc_ty `thenTc` \ (co_fn, lie2) ->
+ returnTc (co_fn <$> expr', lie1 `plusLIE` lie2)
\end{code}
-\begin{code}
-tcMonoExpr (HsIPVar name) res_ty
- = newIPDict (IPOcc name) name res_ty `thenNF_Tc` \ ip ->
- returnNF_Tc (HsIPVar (instToId ip), unitLIE ip)
-\end{code}
%************************************************************************
%* *
= tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
returnTc (HsLam match', lie)
-tcMonoExpr (HsApp e1 e2) res_ty = accum e1 [e2]
- where
- accum (HsApp e1 e2) args = accum e1 (e2:args)
- accum fun args
- = tcApp fun args res_ty `thenTc` \ (fun', args', lie) ->
- returnTc (foldl HsApp fun' args', lie)
-
--- equivalent to (op e1) e2:
-tcMonoExpr (OpApp arg1 op fix arg2) res_ty
- = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) ->
- returnTc (OpApp arg1' op' fix arg2', lie)
+tcMonoExpr (HsApp e1 e2) res_ty
+ = tcApp e1 [e2] res_ty
\end{code}
Note that the operators in sections are expected to be binary, and
-- or just
-- op e
-tcMonoExpr in_expr@(SectionL arg op) res_ty
- = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) ->
-
- -- Check that res_ty is a function type
- -- Without this check we barf in the desugarer on
- -- f op = (3 `op`)
- -- because it tries to desugar to
- -- f op = \r -> 3 op r
- -- so (3 `op`) had better be a function!
- tcAddErrCtxt (sectionLAppCtxt in_expr) $
- unifyFunTy res_ty `thenTc_`
-
- returnTc (SectionL arg' op', lie)
+tcMonoExpr in_expr@(SectionL arg1 op) res_ty
+ = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
+ split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
+ tcArg op (arg1, arg1_ty, 1) `thenTc` \ (arg1',lie2) ->
+ tcAddErrCtxt (exprCtxt in_expr) $
+ tcSub res_ty (mkFunTy arg2_ty op_res_ty) `thenTc` \ (co_fn, lie3) ->
+ returnTc (co_fn <$> SectionL arg1' op', lie1 `plusLIE` lie2 `plusLIE` lie3)
-- Right sections, equivalent to \ x -> x op expr, or
-- \ x -> op x expr
-tcMonoExpr in_expr@(SectionR op expr) res_ty
- = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
- tcAddErrCtxt (sectionRAppCtxt in_expr) $
- split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
- tcMonoExpr expr arg2_ty `thenTc` \ (expr',lie2) ->
- unifyTauTy res_ty (mkFunTy arg1_ty op_res_ty) `thenTc_`
- returnTc (SectionR op' expr', lie1 `plusLIE` lie2)
+tcMonoExpr in_expr@(SectionR op arg2) res_ty
+ = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
+ split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
+ tcArg op (arg2, arg2_ty, 2) `thenTc` \ (arg2',lie2) ->
+ tcAddErrCtxt (exprCtxt in_expr) $
+ tcSub res_ty (mkFunTy arg1_ty op_res_ty) `thenTc` \ (co_fn, lie3) ->
+ returnTc (co_fn <$> SectionR op' arg2', lie1 `plusLIE` lie2 `plusLIE` lie3)
+
+-- equivalent to (op e1) e2:
+
+tcMonoExpr in_expr@(OpApp arg1 op fix arg2) res_ty
+ = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
+ split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
+ tcArg op (arg1, arg1_ty, 1) `thenTc` \ (arg1',lie2a) ->
+ tcArg op (arg2, arg2_ty, 2) `thenTc` \ (arg2',lie2b) ->
+ tcAddErrCtxt (exprCtxt in_expr) $
+ tcSub res_ty op_res_ty `thenTc` \ (co_fn, lie3) ->
+ returnTc (OpApp arg1' op' fix arg2',
+ lie1 `plusLIE` lie2a `plusLIE` lie2b `plusLIE` lie3)
\end{code}
The interesting thing about @ccall@ is that it is just a template
%************************************************************************
%* *
-\subsection{Expressions type signatures}
+\subsection{Implicit Parameter bindings}
%* *
%************************************************************************
\begin{code}
-tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
- = tcHsSigType ExprSigCtxt poly_ty `thenTc` \ sig_tc_ty ->
-
- tcAddErrCtxt (exprSigCtxt in_expr) $
- if not (isQualifiedTy sig_tc_ty) then
- -- Easy case
- unifyTauTy sig_tc_ty res_ty `thenTc_`
- tcMonoExpr expr sig_tc_ty
-
- else -- Signature is polymorphic
- tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
-
- -- Now match the signature type with res_ty.
- -- We must not do this earlier, because res_ty might well
- -- mention variables free in the environment, and we'd get
- -- bogus complaints about not being able to for-all the
- -- sig_tyvars
- unifyTauTy res_ty expr_ty `thenTc_`
-
- -- If everything is ok, return the stuff unchanged, except for
- -- the effect of any substutions etc. We simply discard the
- -- result of the tcSimplifyCheck (inside tcPolyExpr), except for any default
- -- resolution it may have done, which is recorded in the
- -- substitution.
- returnTc (expr, lie)
-\end{code}
-
-Implicit Parameter bindings.
-
-\begin{code}
tcMonoExpr (HsWith expr binds) res_ty
= tcMonoExpr expr res_ty `thenTc` \ (expr', expr_lie) ->
- mapAndUnzipTc tcIPBind binds `thenTc` \ (pairs, bind_lies) ->
+ mapAndUnzip3Tc tcIPBind binds `thenTc` \ (avail_ips, binds', bind_lies) ->
-- If the binding binds ?x = E, we must now
-- discharge any ?x constraints in expr_lie
- tcSimplifyIPs (map fst pairs) expr_lie `thenTc` \ (expr_lie', dict_binds) ->
+ tcSimplifyIPs avail_ips expr_lie `thenTc` \ (expr_lie', dict_binds) ->
let
- binds' = [(instToId ip, rhs) | (ip,rhs) <- pairs]
expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
in
returnTc (HsWith expr'' binds', expr_lie' `plusLIE` plusLIEs bind_lies)
-tcIPBind (name, expr)
+tcIPBind (ip, expr)
= newTyVarTy openTypeKind `thenTc` \ ty ->
tcGetSrcLoc `thenTc` \ loc ->
- newIPDict (IPBind name) name ty `thenNF_Tc` \ ip ->
+ newIPDict (IPBind ip) ip ty `thenNF_Tc` \ (ip', ip_inst) ->
tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
- returnTc ((ip, expr'), lie)
+ returnTc (ip_inst, (ip', expr'), lie)
\end{code}
%************************************************************************
tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
-> TcType -- Expected result type of application
- -> TcM (TcExpr, [TcExpr], -- Translated fun and args
- LIE)
+ -> TcM (TcExpr, LIE) -- Translated fun and args
+
+tcApp (HsApp e1 e2) args res_ty
+ = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
tcApp fun args res_ty
= -- First type-check the function
) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
-- Unify with expected result before type-checking the args
+ -- so that the info from res_ty percolates to expected_arg_tys
-- This is when we might detect a too-few args situation
- tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
- unifyTauTy res_ty actual_result_ty
- ) `thenTc_`
+ tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
+ (tcSub res_ty actual_result_ty) `thenTc` \ (co_fn, lie_res) ->
-- Now typecheck the args
mapAndUnzipTc (tcArg fun)
(zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
- -- Check that the result type doesn't have any nested for-alls.
- -- For example, a "build" on its own is no good; it must be applied to something.
- checkTc (isTauTy actual_result_ty)
- (lurkingRank2Err fun actual_result_ty) `thenTc_`
-
- returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
+ returnTc (co_fn <$> foldl HsApp fun' args',
+ lie_res `plusLIE` lie_fun `plusLIE` plusLIEs lie_args_s)
-- If an error happens we try to figure out whether the
split_fun_ty :: TcType -- The type of the function
- -> Int -- Number of arguments
+ -> Int -- Number of arguments
-> TcM ([TcType], -- Function argument types
- TcType) -- Function result types
+ TcType) -- Function result types
split_fun_ty fun_ty 0
= returnTc ([], fun_ty)
\end{code}
\begin{code}
-tcArg :: RenamedHsExpr -- The function (for error messages)
- -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
- -> TcM (TcExpr, LIE) -- Resulting argument and LIE
+tcArg :: RenamedHsExpr -- The function (for error messages)
+ -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
+ -> TcM (TcExpr, LIE) -- Resulting argument and LIE
tcArg the_fun (arg, expected_arg_ty, arg_no)
= tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
-- The caller of tcRecordBinds has already checked
-- that all the fields come from the same type
- tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
+ tcExpr rhs field_ty `thenTc` \ (rhs', lie) ->
returnTc ((sel_id, rhs', pun_flag), lie)
predCtxt expr
= hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
-sectionRAppCtxt expr
- = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
-
-sectionLAppCtxt expr
- = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
+exprCtxt expr
+ = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
funAppCtxt fun arg arg_no
= hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
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