\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,
+ emptyLIE, plusLIE, LIE, mkLIE, unitLIE, instToId, isEmptyLIE,
newMethod, newOverloadedLit, newDicts
)
-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 ( tcInstTyVars, newTyVarTy, getTcTyVar, putTcTyVar )
+import TcType ( TcType, TcTyVar, TcSigmaType,
+ mkTyConApp, mkClassPred, liftedTypeKind, tcGetTyVar_maybe,
+ isHoleTyVar, openTypeKind )
+import TcUnify ( tcSub, unifyTauTy, unifyListTy, 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 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
+ | Just tv <- tcGetTyVar_maybe pat_ty,
+ isHoleTyVar tv
+ -- 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.
+ = getTcTyVar tv `thenNF_Tc` \ maybe_ty ->
+ case maybe_ty of
+ Just ty -> tcMonoPatBndr binder_name ty
+ Nothing -> newTyVarTy openTypeKind `thenNF_Tc` \ ty ->
+ putTcTyVar tv ty `thenNF_Tc_`
+ returnTc (idCoercion, emptyLIE, mkLocalId binder_name ty)
+ | otherwise
+ = 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
+ -> TcSigmaType -- 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 <$> (AsPat bndr_id pat'), lie_req1 `plusLIE` lie_req1,
tvs, (name, bndr_id) `consBag` ids, lie_avail)
tcPat tc_bndr WildPatIn pat_ty
= tcPat tc_bndr parend_pat pat_ty
tcPat tc_bndr (SigPatIn pat sig) pat_ty
- = tcHsSigType PatSigCtxt sig `thenTc` \ sig_ty ->
-
- -- Check that the signature isn't a polymorphic one, which
- -- we don't permit (at present, anyway)
- checkTc (isTauTy sig_ty) (polyPatSig sig_ty) `thenTc_`
-
- unifyTauTy pat_ty sig_ty `thenTc_`
- tcPat tc_bndr pat sig_ty
+ = tcHsSigType PatSigCtxt sig `thenTc` \ sig_ty ->
+ tcSubPat sig_ty pat_ty `thenTc` \ (co_fn, lie_sig) ->
+ tcPat tc_bndr pat sig_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
+ returnTc (co_fn <$> pat', lie_req `plusLIE` lie_sig, tvs, ids, lie_avail)
\end{code}
+
%************************************************************************
%* *
\subsection{Explicit lists and tuples}
arity = length pats
\end{code}
+
%************************************************************************
%* *
\subsection{Other constructors}
\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) ->
-- 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) ->
+ newOverloadedLit origin lit pat_ty `thenNF_Tc` \ (over_lit_expr, lie2) ->
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
= -- Check that it's a constructor
tcLookupDataCon con_name `thenNF_Tc` \ data_con ->
%************************************************************************
%* *
+\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 -> TcSigmaType -> TcM (PatCoFn, LIE)
+
+tcSubPat sig_ty exp_ty
+ = tcSub exp_ty sig_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 SLIT("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}
%* *
%************************************************************************
projects / ghc-hetmet.git / blobdiff