%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[Main_match]{The @match@ function}
\begin{code}
-#include "HsVersions.h"
-
-module Match ( match, matchWrapper, matchSimply ) where
+module Match ( match, matchExport, matchWrapper, matchSimply, matchSinglePat ) where
-IMP_Ubiq()
-IMPORT_DELOOPER(DsLoop) -- here for paranoia-checking reasons
- -- and to break dsExpr/dsBinds-ish loop
+#include "HsVersions.h"
-import CmdLineOpts ( opt_WarnIncompletePatterns )
+import {-# SOURCE #-} DsExpr( dsExpr )
+import CmdLineOpts ( DynFlag(..), dopt )
import HsSyn
-import TcHsSyn ( SYN_IE(TypecheckedPat), SYN_IE(TypecheckedMatch),
- SYN_IE(TypecheckedHsBinds), SYN_IE(TypecheckedHsExpr) )
-import DsHsSyn ( outPatType, collectTypedPatBinders )
+import TcHsSyn ( TypecheckedPat, TypecheckedMatch, TypecheckedMatchContext, hsPatType )
+import Check ( check, ExhaustivePat )
import CoreSyn
-
-import CoreUtils ( coreExprType )
+import CoreUtils ( bindNonRec )
import DsMonad
import DsGRHSs ( dsGRHSs )
import DsUtils
+import Id ( idType, recordSelectorFieldLabel, Id )
+import DataCon ( dataConFieldLabels, dataConInstOrigArgTys )
import MatchCon ( matchConFamily )
import MatchLit ( matchLiterals )
+import PrelInfo ( pAT_ERROR_ID )
+import TcType ( mkTyVarTys, Type, tcTyConAppArgs, tcEqType )
+import TysWiredIn ( consDataCon, mkTupleTy, mkListTy,
+ tupleCon, parrFakeCon, mkPArrTy )
+import BasicTypes ( Boxity(..) )
+import UniqSet
+import SrcLoc ( noSrcLoc )
+import Util ( lengthExceeds, isSingleton, notNull )
+import Outputable
+\end{code}
+
+This function is a wrapper of @match@, it must be called from all the parts where
+it was called match, but only substitutes the firs call, ....
+if the associated flags are declared, warnings will be issued.
+It can not be called matchWrapper because this name already exists :-(
+
+JJCQ 30-Nov-1997
+
+\begin{code}
+matchExport :: [Id] -- Vars rep'ing the exprs we're matching with
+ -> [EquationInfo] -- Info about patterns, etc. (type synonym below)
+ -> DsM MatchResult -- Desugared result!
+
+
+matchExport vars qs
+ = getDOptsDs `thenDs` \ dflags ->
+ matchExport_really dflags vars qs
+
+matchExport_really dflags vars qs@((EqnInfo _ ctx _ (MatchResult _ _)) : _)
+ | incomplete && shadow =
+ dsShadowWarn ctx eqns_shadow `thenDs` \ () ->
+ dsIncompleteWarn ctx pats `thenDs` \ () ->
+ match vars qs
+ | incomplete =
+ dsIncompleteWarn ctx pats `thenDs` \ () ->
+ match vars qs
+ | shadow =
+ dsShadowWarn ctx eqns_shadow `thenDs` \ () ->
+ match vars qs
+ | otherwise =
+ match vars qs
+ where (pats,indexs) = check qs
+ incomplete = dopt Opt_WarnIncompletePatterns dflags
+ && (notNull pats)
+ shadow = dopt Opt_WarnOverlappingPatterns dflags
+ && sizeUniqSet indexs < no_eqns
+ no_eqns = length qs
+ unused_eqns = uniqSetToList (mkUniqSet [1..no_eqns] `minusUniqSet` indexs)
+ eqns_shadow = map (\n -> qs!!(n - 1)) unused_eqns
+\end{code}
+
+This variable shows the maximum number of lines of output generated for warnings.
+It will limit the number of patterns/equations displayed to@ maximum_output@.
+
+(ToDo: add command-line option?)
+
+\begin{code}
+maximum_output = 4
+\end{code}
+
+The next two functions create the warning message.
+
+\begin{code}
+dsShadowWarn :: DsMatchContext -> [EquationInfo] -> DsM ()
+dsShadowWarn ctx@(DsMatchContext kind _ _) qs = dsWarn warn
+ where
+ warn | qs `lengthExceeds` maximum_output
+ = pp_context ctx (ptext SLIT("are overlapped"))
+ (\ f -> vcat (map (ppr_eqn f kind) (take maximum_output qs)) $$
+ ptext SLIT("..."))
+ | otherwise
+ = pp_context ctx (ptext SLIT("are overlapped"))
+ (\ f -> vcat $ map (ppr_eqn f kind) qs)
+
+
+dsIncompleteWarn :: DsMatchContext -> [ExhaustivePat] -> DsM ()
+dsIncompleteWarn ctx@(DsMatchContext kind _ _) pats = dsWarn warn
+ where
+ warn = pp_context ctx (ptext SLIT("are non-exhaustive"))
+ (\f -> hang (ptext SLIT("Patterns not matched:"))
+ 4 ((vcat $ map (ppr_incomplete_pats kind)
+ (take maximum_output pats))
+ $$ dots))
+
+ dots | pats `lengthExceeds` maximum_output = ptext SLIT("...")
+ | otherwise = empty
+
+pp_context NoMatchContext msg rest_of_msg_fun
+ = (noSrcLoc, ptext SLIT("Some match(es)") <+> hang msg 8 (rest_of_msg_fun id))
+
+pp_context (DsMatchContext kind pats loc) msg rest_of_msg_fun
+ = (loc, vcat [ptext SLIT("Pattern match(es)") <+> msg,
+ sep [ppr_match <> char ':', nest 4 (rest_of_msg_fun pref)]])
+ where
+ (ppr_match, pref)
+ = case kind of
+ FunRhs fun -> (pprMatchContext kind, \ pp -> ppr fun <+> pp)
+ other -> (pprMatchContext kind, \ pp -> pp)
+
+ppr_pats pats = sep (map ppr pats)
-import FieldLabel ( FieldLabel {- Eq instance -} )
-import Id ( idType, dataConFieldLabels,
- dataConArgTys, recordSelectorFieldLabel,
- GenId{-instance-}, SYN_IE(Id)
- )
-import Name ( Name {--O only-} )
-import PprStyle ( PprStyle(..) )
-import PprType ( GenType{-instance-}, GenTyVar{-ditto-} )
-import Pretty ( Doc )
-import PrelVals ( pAT_ERROR_ID )
-import Type ( isPrimType, eqTy, getAppDataTyConExpandingDicts,
- instantiateTauTy, SYN_IE(Type)
- )
-import TyVar ( GenTyVar{-instance Eq-}, SYN_IE(TyVar) )
-import TysPrim ( intPrimTy, charPrimTy, floatPrimTy, doublePrimTy,
- addrPrimTy, wordPrimTy
- )
-import TysWiredIn ( nilDataCon, consDataCon, mkTupleTy, mkListTy,
- charTy, charDataCon, intTy, intDataCon,
- floatTy, floatDataCon, doubleTy, tupleCon,
- doubleDataCon, stringTy, addrTy,
- addrDataCon, wordTy, wordDataCon
- )
-import Unique ( Unique{-instance Eq-} )
-import Util ( panic, pprPanic, assertPanic )
-#if __GLASGOW_HASKELL__ >= 202
-import Outputable ( Outputable(..) )
-#endif
+ppr_shadow_pats kind pats
+ = sep [ppr_pats pats, matchSeparator kind, ptext SLIT("...")]
+
+ppr_incomplete_pats kind (pats,[]) = ppr_pats pats
+ppr_incomplete_pats kind (pats,constraints) =
+ sep [ppr_pats pats, ptext SLIT("with"),
+ sep (map ppr_constraint constraints)]
+
+ppr_constraint (var,pats) = sep [ppr var, ptext SLIT("`notElem`"), ppr pats]
+
+ppr_eqn prefixF kind (EqnInfo _ _ pats _) = prefixF (ppr_shadow_pats kind pats)
\end{code}
+
The function @match@ is basically the same as in the Wadler chapter,
except it is monadised, to carry around the name supply, info about
annotations, etc.
\begin{code}
match :: [Id] -- Variables rep'ing the exprs we're matching with
-> [EquationInfo] -- Info about patterns, etc. (type synonym below)
- -> [EquationInfo] -- Potentially shadowing equations above this one
-> DsM MatchResult -- Desugared result!
\end{code}
patterns in column~1, or they all have constructor patterns in ...
(see ``the mixture rule'' in SLPJ).
\item
-Call @matchUnmixedEqns@ on each block of equations; it will do the
+Call @matchEqnBlock@ on each block of equations; it will do the
appropriate thing for each kind of column-1 pattern, usually ending up
in a recursive call to @match@.
\end{enumerate}
And gluing the ``success expressions'' together isn't quite so pretty.
\begin{code}
-match [] eqns_info shadows
- = complete_matches eqns_info (any eqn_cant_fail shadows)
+match [] eqns_info
+ = returnDs (foldr1 combineMatchResults match_results)
where
- complete_matches [eqn] is_shadowed
- = complete_match eqn is_shadowed
-
- complete_matches (eqn:eqns) is_shadowed
- = complete_match eqn is_shadowed `thenDs` \ match_result1 ->
- complete_matches eqns (is_shadowed || eqn_cant_fail eqn) `thenDs` \ match_result2 ->
- combineMatchResults match_result1 match_result2
-
- -- If at this stage we find that at least one of the shadowing
- -- equations is guaranteed not to fail, then warn of an overlapping pattern
- complete_match (EqnInfo [] match_result@(MatchResult _ _ _ cxt)) is_shadowed
- | is_shadowed = dsShadowWarn cxt `thenDs` \ _ ->
- returnDs match_result
-
- | otherwise = returnDs match_result
-
- eqn_cant_fail :: EquationInfo -> Bool
- eqn_cant_fail (EqnInfo [] (MatchResult CanFail _ _ _)) = False
- eqn_cant_fail (EqnInfo [] (MatchResult CantFail _ _ _)) = True
+ match_results = [ ASSERT( null pats) mr
+ | EqnInfo _ _ pats mr <- eqns_info ]
\end{code}
+
%************************************************************************
%* *
%* match: non-empty rule *
corresponds roughly to @matchVarCon@.
\begin{code}
-match vars@(v:vs) eqns_info shadows
+match vars@(v:vs) eqns_info
= mapDs (tidyEqnInfo v) eqns_info `thenDs` \ tidy_eqns_info ->
- mapDs (tidyEqnInfo v) shadows `thenDs` \ tidy_shadows ->
let
tidy_eqns_blks = unmix_eqns tidy_eqns_info
in
- match_unmixed_eqn_blks vars tidy_eqns_blks tidy_shadows
+ mapDs (matchEqnBlock vars) tidy_eqns_blks `thenDs` \ match_results ->
+ returnDs (foldr1 combineMatchResults match_results)
where
unmix_eqns [] = []
unmix_eqns [eqn] = [ [eqn] ]
- unmix_eqns (eq1@(EqnInfo (p1:p1s) _) : eq2@(EqnInfo (p2:p2s) _) : eqs)
- = if ( (irrefutablePat p1 && irrefutablePat p2)
- || (isConPat p1 && isConPat p2)
- || (isLitPat p1 && isLitPat p2) ) then
+ unmix_eqns (eq1@(EqnInfo _ _ (p1:p1s) _) : eq2@(EqnInfo _ _ (p2:p2s) _) : eqs)
+ = if ( (isWildPat p1 && isWildPat p2)
+ || (isConPat p1 && isConPat p2)
+ || (isLitPat p1 && isLitPat p2) ) then
eq1 `tack_onto` unmixed_rest
else
[ eq1 ] : unmixed_rest
unmixed_rest = unmix_eqns (eq2:eqs)
x `tack_onto` xss = ( x : head xss) : tail xss
-
- -----------------------------------------------------------------------
- -- loop through the blocks:
- -- subsequent blocks create a "fail expr" for the first one...
- match_unmixed_eqn_blks :: [Id]
- -> [ [EquationInfo] ] -- List of eqn BLOCKS
- -> [EquationInfo] -- Shadows
- -> DsM MatchResult
-
- match_unmixed_eqn_blks vars [] shadows = panic "match_unmixed_eqn_blks"
-
- match_unmixed_eqn_blks vars [eqn_blk] shadows = matchUnmixedEqns vars eqn_blk shadows
-
- match_unmixed_eqn_blks vars (eqn_blk:eqn_blks) shadows
- = matchUnmixedEqns vars eqn_blk shadows `thenDs` \ match_result1 -> -- try to match with first blk
- match_unmixed_eqn_blks vars eqn_blks shadows' `thenDs` \ match_result2 ->
- combineMatchResults match_result1 match_result2
- where
- shadows' = eqn_blk ++ shadows
\end{code}
Tidy up the leftmost pattern in an @EquationInfo@, given the variable @v@
\item
Removing lazy (irrefutable) patterns (you don't want to know...).
\item
-Converting explicit tuple- and list-pats into ordinary @ConPats@.
+Converting explicit tuple-, list-, and parallel-array-pats into ordinary
+@ConPats@.
\item
Convert the literal pat "" to [].
\end{itemize}
Float, Double, at least) are converted to unboxed form; e.g.,
\tr{(NPat (HsInt i) _ _)} is converted to:
\begin{verbatim}
-(ConPat I# _ _ [LitPat (HsIntPrim i) _])
+(ConPat I# _ _ [LitPat (HsIntPrim i)])
\end{verbatim}
\end{description}
-- DsM'd because of internal call to "match".
-- "tidy1" does the interesting stuff, looking at
-- one pattern and fiddling the list of bindings.
-tidyEqnInfo v (EqnInfo (pat : pats) match_result)
+ --
+ -- POST CONDITION: head pattern in the EqnInfo is
+ -- WildPat
+ -- ConPat
+ -- NPat
+ -- LitPat
+ -- NPlusKPat
+ -- SigPat
+ -- but no other
+
+tidyEqnInfo v (EqnInfo n ctx (pat : pats) match_result)
= tidy1 v pat match_result `thenDs` \ (pat', match_result') ->
- returnDs (EqnInfo (pat' : pats) match_result')
-
-tidy1 :: Id -- The Id being scrutinised
- -> TypecheckedPat -- The pattern against which it is to be matched
- -> MatchResult -- Current thing do do after matching
- -> DsM (TypecheckedPat, -- Equivalent pattern
- MatchResult) -- Augmented thing to do afterwards
- -- The augmentation usually takes the form
- -- of new bindings to be added to the front
-
+ returnDs (EqnInfo n ctx (pat' : pats) match_result')
+
+
+tidy1 :: Id -- The Id being scrutinised
+ -> TypecheckedPat -- The pattern against which it is to be matched
+ -> MatchResult -- Current thing do do after matching
+ -> DsM (TypecheckedPat, -- Equivalent pattern
+ MatchResult) -- Augmented thing to do afterwards
+ -- The augmentation usually takes the form
+ -- of new bindings to be added to the front
+
+-------------------------------------------------------
+-- (pat', mr') = tidy1 v pat mr
+-- tidies the *outer level only* of pat, giving pat'
+-- It eliminates many pattern forms (as-patterns, variable patterns,
+-- list patterns, etc) yielding one of:
+-- WildPat
+-- ConPat
+-- LitPat
+-- NPat
+-- NPlusKPat
+--
+
+tidy1 v (ParPat pat) match_result
+ = tidy1 v pat match_result
+
+ -- case v of { x -> mr[] }
+ -- = case v of { _ -> let x=v in mr[] }
tidy1 v (VarPat var) match_result
- = returnDs (WildPat (idType var),
- mkCoLetsMatchResult extra_binds match_result)
+ = returnDs (WildPat (idType var), match_result')
where
- extra_binds | v == var = []
- | otherwise = [NonRec var (Var v)]
+ match_result' | v == var = match_result
+ | otherwise = adjustMatchResult (bindNonRec var (Var v)) match_result
+ -- case v of { x@p -> mr[] }
+ -- = case v of { p -> let x=v in mr[] }
tidy1 v (AsPat var pat) match_result
- = tidy1 v pat (mkCoLetsMatchResult extra_binds match_result)
+ = tidy1 v pat match_result'
where
- extra_binds | v == var = []
- | otherwise = [NonRec var (Var v)]
+ match_result' | v == var = match_result
+ | otherwise = adjustMatchResult (bindNonRec var (Var v)) match_result
tidy1 v (WildPat ty) match_result
= returnDs (WildPat ty, match_result)
-- re-express <con-something> as (ConPat ...) [directly]
-tidy1 v (ConOpPat pat1 id pat2 ty) match_result
- = returnDs (ConPat id ty [pat1, pat2], match_result)
-
-tidy1 v (RecPat con_id pat_ty rpats) match_result
- = returnDs (ConPat con_id pat_ty pats, match_result)
+tidy1 v (ConPatOut con ps pat_ty ex_tvs dicts) match_result
+ = returnDs (ConPatOut con tidy_ps pat_ty ex_tvs dicts, match_result)
where
- pats = map mk_pat tagged_arg_tys
-
- -- Boring stuff to find the arg-tys of the constructor
- (_, inst_tys, _) = {-trace "Match.getAppDataTyConExpandingDicts" $-} getAppDataTyConExpandingDicts pat_ty
- con_arg_tys' = dataConArgTys con_id inst_tys
- tagged_arg_tys = con_arg_tys' `zip` (dataConFieldLabels con_id)
+ tidy_ps = PrefixCon (tidy_con con pat_ty ex_tvs ps)
- -- mk_pat picks a WildPat of the appropriate type for absent fields,
- -- and the specified pattern for present fields
- mk_pat (arg_ty, lbl) = case [pat | (sel_id,pat,_) <- rpats,
- recordSelectorFieldLabel sel_id == lbl
- ] of
- (pat:pats) -> ASSERT( null pats )
- pat
- [] -> WildPat arg_ty
-
-tidy1 v (ListPat ty pats) match_result
+tidy1 v (ListPat pats ty) match_result
= returnDs (list_ConPat, match_result)
where
- list_ty = mkListTy ty
- list_ConPat
- = foldr (\ x -> \y -> ConPat consDataCon list_ty [x, y])
- (ConPat nilDataCon list_ty [])
- pats
+ list_ty = mkListTy ty
+ list_ConPat = foldr (\ x y -> mkPrefixConPat consDataCon [x, y] list_ty)
+ (mkNilPat list_ty)
+ pats
+
+-- introduce fake parallel array constructors to be able to handle parallel
+-- arrays with the existing machinery for constructor pattern
+--
+tidy1 v (PArrPat pats ty) match_result
+ = returnDs (parrConPat, match_result)
+ where
+ arity = length pats
+ parrConPat = mkPrefixConPat (parrFakeCon arity) pats (mkPArrTy ty)
-tidy1 v (TuplePat pats) match_result
+tidy1 v (TuplePat pats boxity) match_result
= returnDs (tuple_ConPat, match_result)
where
arity = length pats
- tuple_ConPat
- = ConPat (tupleCon arity)
- (mkTupleTy arity (map outPatType pats))
- pats
+ tuple_ConPat = mkPrefixConPat (tupleCon boxity arity) pats
+ (mkTupleTy boxity arity (map hsPatType pats))
tidy1 v (DictPat dicts methods) match_result
= case num_of_d_and_ms of
- 0 -> tidy1 v (TuplePat []) match_result
+ 0 -> tidy1 v (TuplePat [] Boxed) match_result
1 -> tidy1 v (head dict_and_method_pats) match_result
- _ -> tidy1 v (TuplePat dict_and_method_pats) match_result
+ _ -> tidy1 v (TuplePat dict_and_method_pats Boxed) match_result
where
num_of_d_and_ms = length dicts + length methods
dict_and_method_pats = map VarPat (dicts ++ methods)
-
--- deeply ugly mangling for some (common) NPats/LitPats
-
--- LitPats: the desugarer only sees these at well-known types
-
-tidy1 v pat@(LitPat lit lit_ty) match_result
- | isPrimType lit_ty
- = returnDs (pat, match_result)
-
- | lit_ty `eqTy` charTy
- = returnDs (ConPat charDataCon charTy [LitPat (mk_char lit) charPrimTy],
- match_result)
-
- | otherwise = pprPanic "tidy1:LitPat:" (ppr PprDebug pat)
- where
- mk_char (HsChar c) = HsCharPrim c
+-- LitPats: we *might* be able to replace these w/ a simpler form
+tidy1 v pat@(LitPat lit) match_result
+ = returnDs (tidyLitPat lit pat, match_result)
-- NPats: we *might* be able to replace these w/ a simpler form
+tidy1 v pat@(NPatOut lit lit_ty _) match_result
+ = returnDs (tidyNPat lit lit_ty pat, match_result)
+-- and everything else goes through unchanged...
-tidy1 v pat@(NPat lit lit_ty _) match_result
- = returnDs (better_pat, match_result)
- where
- better_pat
- | lit_ty `eqTy` charTy = ConPat charDataCon lit_ty [LitPat (mk_char lit) charPrimTy]
- | lit_ty `eqTy` intTy = ConPat intDataCon lit_ty [LitPat (mk_int lit) intPrimTy]
- | lit_ty `eqTy` wordTy = ConPat wordDataCon lit_ty [LitPat (mk_word lit) wordPrimTy]
- | lit_ty `eqTy` addrTy = ConPat addrDataCon lit_ty [LitPat (mk_addr lit) addrPrimTy]
- | lit_ty `eqTy` floatTy = ConPat floatDataCon lit_ty [LitPat (mk_float lit) floatPrimTy]
- | lit_ty `eqTy` doubleTy = ConPat doubleDataCon lit_ty [LitPat (mk_double lit) doublePrimTy]
-
- -- Convert the literal pattern "" to the constructor pattern [].
- | null_str_lit lit = ConPat nilDataCon lit_ty []
-
- | otherwise = pat
-
- mk_int (HsInt i) = HsIntPrim i
- mk_int l@(HsLitLit s) = l
-
- mk_char (HsChar c) = HsCharPrim c
- mk_char l@(HsLitLit s) = l
-
- mk_word l@(HsLitLit s) = l
-
- mk_addr l@(HsLitLit s) = l
-
- mk_float (HsInt i) = HsFloatPrim (fromInteger i)
- mk_float (HsFrac f) = HsFloatPrim f
- mk_float l@(HsLitLit s) = l
+tidy1 v non_interesting_pat match_result
+ = returnDs (non_interesting_pat, match_result)
- mk_double (HsInt i) = HsDoublePrim (fromInteger i)
- mk_double (HsFrac f) = HsDoublePrim f
- mk_double l@(HsLitLit s) = l
- null_str_lit (HsString s) = _NULL_ s
- null_str_lit other_lit = False
+tidy_con data_con pat_ty ex_tvs (PrefixCon ps) = ps
+tidy_con data_con pat_ty ex_tvs (InfixCon p1 p2) = [p1,p2]
+tidy_con data_con pat_ty ex_tvs (RecCon rpats)
+ | null rpats
+ = -- Special case for C {}, which can be used for
+ -- a constructor that isn't declared to have
+ -- fields at all
+ map WildPat con_arg_tys'
--- and everything else goes through unchanged...
+ | otherwise
+ = map mk_pat tagged_arg_tys
+ where
+ -- Boring stuff to find the arg-tys of the constructor
+ inst_tys = tcTyConAppArgs pat_ty -- Newtypes must be opaque
+ con_arg_tys' = dataConInstOrigArgTys data_con (inst_tys ++ mkTyVarTys ex_tvs)
+ tagged_arg_tys = con_arg_tys' `zip` (dataConFieldLabels data_con)
-tidy1 v non_interesting_pat match_result
- = returnDs (non_interesting_pat, match_result)
+ -- mk_pat picks a WildPat of the appropriate type for absent fields,
+ -- and the specified pattern for present fields
+ mk_pat (arg_ty, lbl) = case [pat | (sel_id,pat) <- rpats,
+ recordSelectorFieldLabel sel_id == lbl
+ ] of
+ (pat:pats) -> ASSERT( null pats )
+ pat
+ [] -> WildPat arg_ty
\end{code}
-PREVIOUS matchTwiddled STUFF:
+\noindent
+{\bf Previous @matchTwiddled@ stuff:}
Now we get to the only interesting part; note: there are choices for
translation [from Simon's notes]; translation~1:
%* match on an unmixed block: the real business *
%* *
%************************************************************************
-\subsection[matchUnmixedEqns]{@matchUnmixedEqns@: getting down to business}
+\subsection[matchEqnBlock]{@matchEqnBlock@: getting down to business}
-The function @matchUnmixedEqns@ is where the matching stuff sets to
+The function @matchEqnBlock@ is where the matching stuff sets to
work a block of equations, to which the mixture rule has been applied.
Its arguments and results are the same as for the ``top-level'' @match@.
\begin{code}
-matchUnmixedEqns :: [Id]
- -> [EquationInfo]
- -> [EquationInfo] -- Shadows
- -> DsM MatchResult
+matchEqnBlock :: [Id]
+ -> [EquationInfo]
+ -> DsM MatchResult
-matchUnmixedEqns [] _ _ = panic "matchUnmixedEqns: no names"
+matchEqnBlock [] _ = panic "matchEqnBlock: no names"
-matchUnmixedEqns all_vars@(var:vars) eqns_info shadows
- | irrefutablePat first_pat
- = ASSERT( irrefutablePats column_1_pats ) -- Sanity check
+matchEqnBlock all_vars@(var:vars) eqns_info
+ | isWildPat first_pat
+ = ASSERT( all isWildPat column_1_pats ) -- Sanity check
-- Real true variables, just like in matchVar, SLPJ p 94
- match vars remaining_eqns_info remaining_shadows
+ -- No binding to do: they'll all be wildcards by now (done in tidy)
+ match vars remaining_eqns_info
| isConPat first_pat
= ASSERT( patsAreAllCons column_1_pats )
- matchConFamily all_vars eqns_info shadows
+ matchConFamily all_vars eqns_info
| isLitPat first_pat
= ASSERT( patsAreAllLits column_1_pats )
-- see notes in MatchLiteral
-- not worried about the same literal more than once in a column
-- (ToDo: sort this out later)
- matchLiterals all_vars eqns_info shadows
+ matchLiterals all_vars eqns_info
+ | isSigPat first_pat
+ = ASSERT( isSingleton eqns_info )
+ matchSigPat all_vars (head eqns_info)
where
first_pat = head column_1_pats
- column_1_pats = [pat | EqnInfo (pat:_) _ <- eqns_info]
- remaining_eqns_info = [EqnInfo pats match_result | EqnInfo (_:pats) match_result <- eqns_info]
- remaining_shadows = [EqnInfo pats match_result | EqnInfo (pat:pats) match_result <- shadows,
- irrefutablePat pat ]
- -- Discard shadows which can be refuted, since they don't shadow
- -- a variable
+ column_1_pats = [pat | EqnInfo _ _ (pat:_) _ <- eqns_info]
+ remaining_eqns_info = [EqnInfo n ctx pats match_result | EqnInfo n ctx (_:pats) match_result <- eqns_info]
\end{code}
+A SigPat is a type coercion and must be handled one at at time. We can't
+combine them unless the type of the pattern inside is identical, and we don't
+bother to check for that. For example:
+
+ data T = T1 Int | T2 Bool
+ f :: (forall a. a -> a) -> T -> t
+ f (g::Int->Int) (T1 i) = T1 (g i)
+ f (g::Bool->Bool) (T2 b) = T2 (g b)
+
+We desugar this as follows:
+
+ f = \ g::(forall a. a->a) t::T ->
+ let gi = g Int
+ in case t of { T1 i -> T1 (gi i)
+ other ->
+ let gb = g Bool
+ in case t of { T2 b -> T2 (gb b)
+ other -> fail }}
+
+Note that we do not treat the first column of patterns as a
+column of variables, because the coerced variables (gi, gb)
+would be of different types. So we get rather grotty code.
+But I don't think this is a common case, and if it was we could
+doubtless improve it.
+
+Meanwhile, the strategy is:
+ * treat each SigPat coercion (always non-identity coercions)
+ as a separate block
+ * deal with the stuff inside, and then wrap a binding round
+ the result to bind the new variable (gi, gb, etc)
+
+\begin{code}
+matchSigPat :: [Id] -> EquationInfo -> DsM MatchResult
+matchSigPat (var:vars) (EqnInfo n ctx (SigPatOut pat ty co_fn : pats) result)
+ = selectMatchVar pat `thenDs` \ new_var ->
+ dsExpr (HsApp co_fn (HsVar var)) `thenDs` \ rhs ->
+ match (new_var:vars) [EqnInfo n ctx (pat:pats) result] `thenDs` \ result' ->
+ returnDs (adjustMatchResult (bindNonRec new_var rhs) result')
+\end{code}
+
%************************************************************************
%* *
%* matchWrapper: a convenient way to call @match@ *
\end{enumerate}
\begin{code}
-matchWrapper :: DsMatchKind -- For shadowing warning messages
- -> [TypecheckedMatch] -- Matches being desugared
- -> String -- Error message if the match fails
+matchWrapper :: TypecheckedMatchContext -- For shadowing warning messages
+ -> [TypecheckedMatch] -- Matches being desugared
-> DsM ([Id], CoreExpr) -- Results
+\end{code}
--- a special case for the common ...:
--- just one Match
--- lots of (all?) unfailable pats
--- e.g.,
--- f x y z = ....
-
-matchWrapper kind [(PatMatch (VarPat var) match)] error_string
- = matchWrapper kind [match] error_string `thenDs` \ (vars, core_expr) ->
- returnDs (var:vars, core_expr)
-
-matchWrapper kind [(PatMatch (WildPat ty) match)] error_string
- = newSysLocalDs ty `thenDs` \ var ->
- matchWrapper kind [match] error_string `thenDs` \ (vars, core_expr) ->
- returnDs (var:vars, core_expr)
-
-matchWrapper kind [(GRHSMatch
- (GRHSsAndBindsOut [OtherwiseGRHS expr _] binds _))] error_string
- = dsBinds binds `thenDs` \ core_binds ->
- dsExpr expr `thenDs` \ core_expr ->
- returnDs ([], mkCoLetsAny core_binds core_expr)
+ There is one small problem with the Lambda Patterns, when somebody
+ writes something similar to:
+\begin{verbatim}
+ (\ (x:xs) -> ...)
+\end{verbatim}
+ he/she don't want a warning about incomplete patterns, that is done with
+ the flag @opt_WarnSimplePatterns@.
+ This problem also appears in the:
+\begin{itemize}
+\item @do@ patterns, but if the @do@ can fail
+ it creates another equation if the match can fail
+ (see @DsExpr.doDo@ function)
+\item @let@ patterns, are treated by @matchSimply@
+ List Comprension Patterns, are treated by @matchSimply@ also
+\end{itemize}
-----------------------------------------------------------------------------
--- and all the rest... (general case)
+We can't call @matchSimply@ with Lambda patterns,
+due to the fact that lambda patterns can have more than
+one pattern, and match simply only accepts one pattern.
-matchWrapper kind matches error_string
- = flattenMatches kind matches `thenDs` \ eqns_info@(EqnInfo arg_pats (MatchResult _ result_ty _ _) : _) ->
+JJQC 30-Nov-1997
- selectMatchVars arg_pats `thenDs` \ new_vars ->
- match new_vars eqns_info [] `thenDs` \ match_result ->
+\begin{code}
+matchWrapper ctxt matches
+ = getDOptsDs `thenDs` \ dflags ->
+ flattenMatches ctxt matches `thenDs` \ (result_ty, eqns_info) ->
+ let
+ EqnInfo _ _ arg_pats _ : _ = eqns_info
+ error_string = matchContextErrString ctxt
+ in
+ mapDs selectMatchVar arg_pats `thenDs` \ new_vars ->
+ match_fun dflags new_vars eqns_info `thenDs` \ match_result ->
mkErrorAppDs pAT_ERROR_ID result_ty error_string `thenDs` \ fail_expr ->
-
- -- Check for incomplete pattern match
- (case match_result of
- MatchResult CanFail result_ty match_fn cxt
- | opt_WarnIncompletePatterns
- -> dsIncompleteWarn cxt
- other -> returnDs ()
- ) `thenDs` \ _ ->
-
extractMatchResult match_result fail_expr `thenDs` \ result_expr ->
returnDs (new_vars, result_expr)
+ where match_fun dflags
+ = case ctxt of
+ LambdaExpr | dopt Opt_WarnSimplePatterns dflags -> matchExport
+ | otherwise -> match
+ _ -> matchExport
\end{code}
%************************************************************************
\begin{code}
matchSimply :: CoreExpr -- Scrutinee
- -> TypecheckedPat -- Pattern it should match
- -> Type -- Type of result
+ -> TypecheckedMatchContext -- Match kind
+ -> TypecheckedPat -- Pattern it should match
-> CoreExpr -- Return this if it matches
- -> CoreExpr -- Return this if it does
+ -> CoreExpr -- Return this if it doesn't
-> DsM CoreExpr
-matchSimply (Var var) pat result_ty result_expr fail_expr
- = match [var] [eqn_info] [] `thenDs` \ match_result ->
- extractMatchResult match_result fail_expr
- where
- eqn_info = EqnInfo [pat] initial_match_result
- initial_match_result = MatchResult CantFail
- result_ty
- (\ ignore -> result_expr)
- NoMatchContext
-
-matchSimply scrut_expr pat result_ty result_expr msg
- = newSysLocalDs (outPatType pat) `thenDs` \ scrut_var ->
- matchSimply (Var scrut_var) pat result_ty result_expr msg `thenDs` \ expr ->
- returnDs (Let (NonRec scrut_var scrut_expr) expr)
+matchSimply scrut kind pat result_expr fail_expr
+ = getSrcLocDs `thenDs` \ locn ->
+ let
+ ctx = DsMatchContext kind [pat] locn
+ match_result = cantFailMatchResult result_expr
+ in
+ matchSinglePat scrut ctx pat match_result `thenDs` \ match_result' ->
+ extractMatchResult match_result' fail_expr
-extractMatchResult (MatchResult CantFail _ match_fn _) fail_expr
- = returnDs (match_fn (error "It can't fail!"))
+matchSinglePat :: CoreExpr -> DsMatchContext -> TypecheckedPat
+ -> MatchResult -> DsM MatchResult
-extractMatchResult (MatchResult CanFail result_ty match_fn cxt) fail_expr
- = mkFailurePair result_ty `thenDs` \ (fail_bind_fn, if_it_fails) ->
- returnDs (Let (fail_bind_fn fail_expr) (match_fn if_it_fails))
+matchSinglePat (Var var) ctx pat match_result
+ = getDOptsDs `thenDs` \ dflags ->
+ match_fn dflags [var] [EqnInfo 1 ctx [pat] match_result]
+ where
+ match_fn dflags
+ | dopt Opt_WarnSimplePatterns dflags = matchExport
+ | otherwise = match
+
+matchSinglePat scrut ctx pat match_result
+ = selectMatchVar pat `thenDs` \ var ->
+ matchSinglePat (Var var) ctx pat match_result `thenDs` \ match_result' ->
+ returnDs (adjustMatchResult (bindNonRec var scrut) match_result')
\end{code}
%************************************************************************
%* flattenMatches : create a list of EquationInfo *
%* *
%************************************************************************
+
\subsection[flattenMatches]{@flattenMatches@: create @[EquationInfo]@}
This is actually local to @matchWrapper@.
\begin{code}
-flattenMatches
- :: DsMatchKind
- -> [TypecheckedMatch]
- -> DsM [EquationInfo]
-
-flattenMatches kind [] = returnDs []
+flattenMatches :: TypecheckedMatchContext
+ -> [TypecheckedMatch]
+ -> DsM (Type, [EquationInfo])
-flattenMatches kind (match : matches)
- = flatten_match [] match `thenDs` \ eqn_info ->
- flattenMatches kind matches `thenDs` \ eqn_infos ->
- returnDs (eqn_info : eqn_infos)
+flattenMatches kind matches
+ = mapAndUnzipDs flatten_match (matches `zip` [1..]) `thenDs` \ (result_tys, eqn_infos) ->
+ let
+ result_ty = head result_tys
+ in
+ ASSERT( all (tcEqType result_ty) result_tys )
+ returnDs (result_ty, eqn_infos)
where
- flatten_match :: [TypecheckedPat] -- Reversed list of patterns encountered so far
- -> TypecheckedMatch
- -> DsM EquationInfo
-
- flatten_match pats_so_far (PatMatch pat match)
- = flatten_match (pat:pats_so_far) match
-
- flatten_match pats_so_far (GRHSMatch (GRHSsAndBindsOut grhss binds ty))
- = dsBinds binds `thenDs` \ core_binds ->
- dsGRHSs ty kind pats grhss `thenDs` \ match_result ->
- returnDs (EqnInfo pats (mkCoLetsMatchResult core_binds match_result))
- where
- pats = reverse pats_so_far -- They've accumulated in reverse order
-
- flatten_match pats_so_far (SimpleMatch expr)
- = dsExpr expr `thenDs` \ core_expr ->
- getSrcLocDs `thenDs` \ locn ->
- returnDs (EqnInfo pats
- (MatchResult CantFail (coreExprType core_expr)
- (\ ignore -> core_expr)
- (DsMatchContext kind pats locn)))
-
- -- the matching can't fail, so we won't generate an error message.
- where
- pats = reverse pats_so_far -- They've accumulated in reverse order
-
+ flatten_match (Match pats _ grhss, n)
+ = dsGRHSs kind pats grhss `thenDs` \ (ty, match_result) ->
+ getSrcLocDs `thenDs` \ locn ->
+ returnDs (ty, EqnInfo n (DsMatchContext kind pats locn) pats match_result)
\end{code}
-
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