\section[TcPat]{Typechecking patterns}
\begin{code}
-module TcPat ( tcPat, tcMonoPatBndr, simpleHsLitTy, badFieldCon, polyPatSig ) where
+module TcPat ( tcPat, tcMonoPatBndr, tcSubPat,
+ badFieldCon, polyPatSig
+ ) where
#include "HsVersions.h"
import HsSyn ( InPat(..), OutPat(..), HsLit(..), HsOverLit(..), HsExpr(..) )
import RnHsSyn ( RenamedPat )
-import TcHsSyn ( TcPat, TcId )
+import TcHsSyn ( TcPat, TcId, simpleHsLitTy )
import TcMonad
import Inst ( InstOrigin(..),
- emptyLIE, plusLIE, LIE, mkLIE, unitLIE, instToId,
- newMethod, newOverloadedLit, newDicts
+ emptyLIE, plusLIE, LIE, mkLIE, unitLIE, instToId, isEmptyLIE,
+ newMethod, newMethodFromName, newOverloadedLit, newDicts, tcInstDataCon
)
-import Id ( mkLocalId )
+import Id ( mkLocalId, mkSysLocal )
import Name ( Name )
import FieldLabel ( fieldLabelName )
import TcEnv ( tcLookupClass, tcLookupDataCon, tcLookupGlobalId, tcLookupId )
-import TcMType ( tcInstTyVars, newTyVarTy, unifyTauTy, unifyListTy, unifyTupleTy )
-import TcType ( TcType, TcTyVar, isTauTy, mkTyConApp, mkClassPred, liftedTypeKind )
+import TcMType ( newTyVarTy, zapToType )
+import TcType ( TcType, TcTyVar, TcSigmaType,
+ mkClassPred, liftedTypeKind )
+import TcUnify ( tcSubOff, TcHoleType,
+ unifyTauTy, unifyListTy, unifyPArrTy, unifyTupleTy,
+ mkCoercion, idCoercion, isIdCoercion,
+ (<$>), PatCoFn )
import TcMonoType ( tcHsSigType, UserTypeCtxt(..) )
+import TysWiredIn ( stringTy )
import CmdLineOpts ( opt_IrrefutableTuples )
-import DataCon ( dataConSig, dataConFieldLabels,
- dataConSourceArity
- )
-import Subst ( substTy, substTheta )
-import TysPrim ( charPrimTy, intPrimTy, floatPrimTy,
- doublePrimTy, addrPrimTy
- )
-import TysWiredIn ( charTy, stringTy, intTy, integerTy )
+import DataCon ( dataConFieldLabels, dataConSourceArity )
import PrelNames ( eqStringName, eqName, geName, cCallableClassName )
import BasicTypes ( isBoxed )
import Bag
%************************************************************************
\begin{code}
--- This is the right function to pass to tcPat when
--- we're looking at a lambda-bound pattern,
--- so there's no polymorphic guy to worry about
-tcMonoPatBndr binder_name pat_ty = returnTc (mkLocalId binder_name pat_ty)
+type BinderChecker = Name -> TcSigmaType -> TcM (PatCoFn, LIE, TcId)
+ -- How to construct a suitable (monomorphic)
+ -- Id for variables found in the pattern
+ -- The TcSigmaType is the expected type
+ -- from the pattern context
+
+-- The Id may have a sigma type (e.g. f (x::forall a. a->a))
+-- so we want to *create* it during pattern type checking.
+-- We don't want to make Ids first with a type-variable type
+-- and then unify... becuase we can't unify a sigma type with a type variable.
+
+tcMonoPatBndr :: BinderChecker
+ -- This is the right function to pass to tcPat when
+ -- we're looking at a lambda-bound pattern,
+ -- so there's no polymorphic guy to worry about
+
+tcMonoPatBndr binder_name pat_ty
+ = zapToType pat_ty `thenNF_Tc` \ pat_ty' ->
+ -- If there are *no constraints* on the pattern type, we
+ -- revert to good old H-M typechecking, making
+ -- the type of the binder into an *ordinary*
+ -- type variable. We find out if there are no constraints
+ -- by seeing if we are given an "open hole" as our info.
+ -- What we are trying to avoid here is giving a binder
+ -- a type that is a 'hole'. The only place holes should
+ -- appear is as an argument to tcPat and tcExpr/tcMonoExpr.
+
+ returnTc (idCoercion, emptyLIE, mkLocalId binder_name pat_ty')
\end{code}
%************************************************************************
\begin{code}
-tcPat :: (Name -> TcType -> TcM TcId) -- How to construct a suitable (monomorphic)
- -- Id for variables found in the pattern
- -- The TcType is the expected type, see note below
+tcPat :: BinderChecker
-> RenamedPat
- -> TcType -- Expected type derived from the context
+ -> TcHoleType -- Expected type derived from the context
-- In the case of a function with a rank-2 signature,
-- this type might be a forall type.
- -- INVARIANT: if it is, the foralls will always be visible,
- -- not hidden inside a mutable type variable
-> TcM (TcPat,
LIE, -- Required by n+k and literal pats
= failWithTc (badTypePat pat)
tcPat tc_bndr (VarPatIn name) pat_ty
- = tc_bndr name pat_ty `thenTc` \ bndr_id ->
- returnTc (VarPat bndr_id, emptyLIE, emptyBag, unitBag (name, bndr_id), emptyLIE)
+ = tc_bndr name pat_ty `thenTc` \ (co_fn, lie_req, bndr_id) ->
+ returnTc (co_fn <$> VarPat bndr_id, lie_req,
+ emptyBag, unitBag (name, bndr_id), emptyLIE)
tcPat tc_bndr (LazyPatIn pat) pat_ty
= tcPat tc_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
returnTc (LazyPat pat', lie_req, tvs, ids, lie_avail)
tcPat tc_bndr pat_in@(AsPatIn name pat) pat_ty
- = tc_bndr name pat_ty `thenTc` \ bndr_id ->
- tcPat tc_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
- tcAddErrCtxt (patCtxt pat_in) $
- returnTc (AsPat bndr_id pat', lie_req,
+ = tc_bndr name pat_ty `thenTc` \ (co_fn, lie_req1, bndr_id) ->
+ tcPat tc_bndr pat pat_ty `thenTc` \ (pat', lie_req2, tvs, ids, lie_avail) ->
+ returnTc (co_fn <$> (AsPat bndr_id pat'), lie_req1 `plusLIE` lie_req2,
tvs, (name, bndr_id) `consBag` ids, lie_avail)
tcPat tc_bndr WildPatIn pat_ty
- = returnTc (WildPat pat_ty, emptyLIE, emptyBag, emptyBag, emptyLIE)
+ = zapToType pat_ty `thenNF_Tc` \ pat_ty' ->
+ -- We might have an incoming 'hole' type variable; no annotation
+ -- so zap it to a type. Rather like tcMonoPatBndr.
+ returnTc (WildPat pat_ty', emptyLIE, emptyBag, emptyBag, emptyLIE)
tcPat tc_bndr (ParPatIn parend_pat) pat_ty
= tcPat tc_bndr parend_pat pat_ty
-tcPat tc_bndr (SigPatIn pat sig) pat_ty
- = tcHsSigType PatSigCtxt sig `thenTc` \ sig_ty ->
-
- -- Check that the signature isn't a polymorphic one, which
- -- we don't permit (at present, anyway)
- checkTc (isTauTy sig_ty) (polyPatSig sig_ty) `thenTc_`
-
- unifyTauTy pat_ty sig_ty `thenTc_`
- tcPat tc_bndr pat sig_ty
+tcPat tc_bndr pat_in@(SigPatIn pat sig) pat_ty
+ = tcAddErrCtxt (patCtxt pat_in) $
+ tcHsSigType PatSigCtxt sig `thenTc` \ sig_ty ->
+ tcSubPat sig_ty pat_ty `thenTc` \ (co_fn, lie_sig) ->
+ tcPat tc_bndr pat sig_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
+ returnTc (co_fn <$> pat', lie_req `plusLIE` lie_sig, tvs, ids, lie_avail)
\end{code}
+
%************************************************************************
%* *
-\subsection{Explicit lists and tuples}
+\subsection{Explicit lists, parallel arrays, and tuples}
%* *
%************************************************************************
tcPats tc_bndr pats (repeat elem_ty) `thenTc` \ (pats', lie_req, tvs, ids, lie_avail) ->
returnTc (ListPat elem_ty pats', lie_req, tvs, ids, lie_avail)
+tcPat tc_bndr pat_in@(PArrPatIn pats) pat_ty
+ = tcAddErrCtxt (patCtxt pat_in) $
+ unifyPArrTy pat_ty `thenTc` \ elem_ty ->
+ tcPats tc_bndr pats (repeat elem_ty) `thenTc` \ (pats', lie_req, tvs, ids, lie_avail) ->
+ returnTc (PArrPat elem_ty pats', lie_req, tvs, ids, lie_avail)
+
tcPat tc_bndr pat_in@(TuplePatIn pats boxity) pat_ty
= tcAddErrCtxt (patCtxt pat_in) $
arity = length pats
\end{code}
+
%************************************************************************
%* *
\subsection{Other constructors}
= tcAddErrCtxt (patCtxt pat) $
-- Check the constructor itself
- tcConstructor pat name pat_ty `thenTc` \ (data_con, ex_tvs, dicts, lie_avail1, arg_tys) ->
+ tcConstructor pat name `thenTc` \ (data_con, lie_req1, ex_tvs, ex_dicts, lie_avail1, arg_tys, con_res_ty) ->
+
+ -- Check overall type matches (c.f. tcConPat)
+ tcSubPat con_res_ty pat_ty `thenTc` \ (co_fn, lie_req2) ->
let
-- Don't use zipEqual! If the constructor isn't really a record, then
-- dataConFieldLabels will be empty (and each field in the pattern
in
-- Check the fields
- tc_fields field_tys rpats `thenTc` \ (rpats', lie_req, tvs, ids, lie_avail2) ->
+ tc_fields field_tys rpats `thenTc` \ (rpats', lie_req3, tvs, ids, lie_avail2) ->
- returnTc (RecPat data_con pat_ty ex_tvs dicts rpats',
- lie_req,
+ returnTc (RecPat data_con pat_ty ex_tvs ex_dicts rpats',
+ lie_req1 `plusLIE` lie_req2 `plusLIE` lie_req3,
listToBag ex_tvs `unionBags` tvs,
ids,
lie_avail1 `plusLIE` lie_avail2)
returnTc (LitPat simple_lit pat_ty, emptyLIE, emptyBag, emptyBag, emptyLIE)
tcPat tc_bndr pat@(NPatIn over_lit) pat_ty
- = newOverloadedLit (PatOrigin pat) over_lit pat_ty `thenNF_Tc` \ (over_lit_expr, lie1) ->
- tcLookupGlobalId eqName `thenNF_Tc` \ eq_sel_id ->
- newMethod origin eq_sel_id [pat_ty] `thenNF_Tc` \ eq ->
+ = newOverloadedLit origin over_lit pat_ty `thenNF_Tc` \ (over_lit_expr, lie1) ->
+ newMethodFromName origin pat_ty eqName `thenNF_Tc` \ eq ->
returnTc (NPat lit' pat_ty (HsApp (HsVar (instToId eq)) over_lit_expr),
lie1 `plusLIE` unitLIE eq,
\begin{code}
tcPat tc_bndr pat@(NPlusKPatIn name lit@(HsIntegral i _) minus_name) pat_ty
- = tc_bndr name pat_ty `thenTc` \ bndr_id ->
+ = tc_bndr name pat_ty `thenTc` \ (co_fn, lie1, bndr_id) ->
+ newOverloadedLit origin lit pat_ty `thenNF_Tc` \ (over_lit_expr, lie2) ->
+ newMethodFromName origin pat_ty geName `thenNF_Tc` \ ge ->
+
-- The '-' part is re-mappable syntax
tcLookupId minus_name `thenNF_Tc` \ minus_sel_id ->
- tcLookupGlobalId geName `thenNF_Tc` \ ge_sel_id ->
- newOverloadedLit origin lit pat_ty `thenNF_Tc` \ (over_lit_expr, lie1) ->
- newMethod origin ge_sel_id [pat_ty] `thenNF_Tc` \ ge ->
newMethod origin minus_sel_id [pat_ty] `thenNF_Tc` \ minus ->
returnTc (NPlusKPat bndr_id i pat_ty
(SectionR (HsVar (instToId ge)) over_lit_expr)
(SectionR (HsVar (instToId minus)) over_lit_expr),
- lie1 `plusLIE` mkLIE [ge,minus],
+ lie1 `plusLIE` lie2 `plusLIE` mkLIE [ge,minus],
emptyBag, unitBag (name, bndr_id), emptyLIE)
where
origin = PatOrigin pat
Helper functions
\begin{code}
-tcPats :: (Name -> TcType -> TcM TcId) -- How to deal with variables
+tcPats :: BinderChecker -- How to deal with variables
-> [RenamedPat] -> [TcType] -- Excess 'expected types' discarded
-> TcM ([TcPat],
LIE, -- Required by n+k and literal pats
------------------------------------------------------
\begin{code}
-simpleHsLitTy :: HsLit -> TcType
-simpleHsLitTy (HsCharPrim c) = charPrimTy
-simpleHsLitTy (HsStringPrim s) = addrPrimTy
-simpleHsLitTy (HsInt i) = intTy
-simpleHsLitTy (HsInteger i) = integerTy
-simpleHsLitTy (HsIntPrim i) = intPrimTy
-simpleHsLitTy (HsFloatPrim f) = floatPrimTy
-simpleHsLitTy (HsDoublePrim d) = doublePrimTy
-simpleHsLitTy (HsChar c) = charTy
-simpleHsLitTy (HsString str) = stringTy
-\end{code}
-
-
-------------------------------------------------------
-\begin{code}
-tcConstructor pat con_name pat_ty
+tcConstructor pat con_name
= -- Check that it's a constructor
tcLookupDataCon con_name `thenNF_Tc` \ data_con ->
-- Instantiate it
- let
- (tvs, _, ex_tvs, ex_theta, arg_tys, tycon) = dataConSig data_con
- -- Ignore the theta; overloaded constructors only
- -- behave differently when called, not when used for
- -- matching.
- in
- tcInstTyVars (ex_tvs ++ tvs) `thenNF_Tc` \ (all_tvs', ty_args', tenv) ->
- let
- ex_theta' = substTheta tenv ex_theta
- arg_tys' = map (substTy tenv) arg_tys
-
- n_ex_tvs = length ex_tvs
- ex_tvs' = take n_ex_tvs all_tvs'
- result_ty = mkTyConApp tycon (drop n_ex_tvs ty_args')
- in
- newDicts (PatOrigin pat) ex_theta' `thenNF_Tc` \ dicts ->
-
- -- Check overall type matches
- unifyTauTy pat_ty result_ty `thenTc_`
+ tcInstDataCon (PatOrigin pat) data_con `thenNF_Tc` \ (_, ex_dicts, arg_tys, result_ty, lie_req, ex_lie, ex_tvs) ->
- returnTc (data_con, ex_tvs', map instToId dicts, mkLIE dicts, arg_tys')
+ returnTc (data_con, lie_req, ex_tvs, ex_dicts, ex_lie, arg_tys, result_ty)
\end{code}
------------------------------------------------------
= tcAddErrCtxt (patCtxt pat) $
-- Check the constructor itself
- tcConstructor pat con_name pat_ty `thenTc` \ (data_con, ex_tvs', dicts, lie_avail1, arg_tys') ->
+ tcConstructor pat con_name `thenTc` \ (data_con, lie_req1, ex_tvs, ex_dicts, lie_avail1, arg_tys, con_res_ty) ->
+
+ -- Check overall type matches.
+ -- The pat_ty might be a for-all type, in which
+ -- case we must instantiate to match
+ tcSubPat con_res_ty pat_ty `thenTc` \ (co_fn, lie_req2) ->
-- Check correct arity
let
(arityErr "Constructor" data_con con_arity no_of_args) `thenTc_`
-- Check arguments
- tcPats tc_bndr arg_pats arg_tys' `thenTc` \ (arg_pats', lie_req, tvs, ids, lie_avail2) ->
+ tcPats tc_bndr arg_pats arg_tys `thenTc` \ (arg_pats', lie_req3, tvs, ids, lie_avail2) ->
- returnTc (ConPat data_con pat_ty ex_tvs' dicts arg_pats',
- lie_req,
- listToBag ex_tvs' `unionBags` tvs,
+ returnTc (co_fn <$> ConPat data_con pat_ty ex_tvs ex_dicts arg_pats',
+ lie_req1 `plusLIE` lie_req2 `plusLIE` lie_req3,
+ listToBag ex_tvs `unionBags` tvs,
ids,
lie_avail1 `plusLIE` lie_avail2)
\end{code}
%************************************************************************
%* *
+\subsection{Subsumption}
+%* *
+%************************************************************************
+
+Example:
+ f :: (forall a. a->a) -> Int -> Int
+ f (g::Int->Int) y = g y
+This is ok: the type signature allows fewer callers than
+the (more general) signature f :: (Int->Int) -> Int -> Int
+I.e. (forall a. a->a) <= Int -> Int
+We end up translating this to:
+ f = \g' :: (forall a. a->a). let g = g' Int in g' y
+
+tcSubPat does the work
+ sig_ty is the signature on the pattern itself
+ (Int->Int in the example)
+ expected_ty is the type passed inwards from the context
+ (forall a. a->a in the example)
+
+\begin{code}
+tcSubPat :: TcSigmaType -> TcHoleType -> TcM (PatCoFn, LIE)
+
+tcSubPat sig_ty exp_ty
+ = tcSubOff sig_ty exp_ty `thenTc` \ (co_fn, lie) ->
+ -- co_fn is a coercion on *expressions*, and we
+ -- need to make a coercion on *patterns*
+ if isIdCoercion co_fn then
+ ASSERT( isEmptyLIE lie )
+ returnNF_Tc (idCoercion, emptyLIE)
+ else
+ tcGetUnique `thenNF_Tc` \ uniq ->
+ let
+ arg_id = mkSysLocal FSLIT("sub") uniq exp_ty
+ the_fn = DictLam [arg_id] (co_fn <$> HsVar arg_id)
+ pat_co_fn p = SigPat p exp_ty the_fn
+ in
+ returnNF_Tc (mkCoercion pat_co_fn, lie)
+\end{code}
+
+
+%************************************************************************
+%* *
\subsection{Errors and contexts}
%* *
%************************************************************************
\begin{code}
-patCtxt pat = hang (ptext SLIT("In the pattern:"))
+patCtxt pat = hang (ptext SLIT("When checking the pattern:"))
4 (ppr pat)
badFieldCon :: Name -> Name -> SDoc
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