X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2FdeSugar%2FMatch.lhs;h=282ba80464af9e09ae766438ce3fc8c651cbe06b;hb=e0445ffa5a89632b542e7d7bc2ad46d944716453;hp=eea766773db945c8e9e5af900ec335c9ee92cee5;hpb=9d4c03805bafb6b1e1d47306b6a6c591c998e517;p=ghc-hetmet.git diff --git a/ghc/compiler/deSugar/Match.lhs b/ghc/compiler/deSugar/Match.lhs index eea7667..282ba80 100644 --- a/ghc/compiler/deSugar/Match.lhs +++ b/ghc/compiler/deSugar/Match.lhs @@ -1,55 +1,143 @@ % -% (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 HsSyn hiding ( collectBinders{-also from CoreSyn-} ) -import TcHsSyn ( SYN_IE(TypecheckedPat), SYN_IE(TypecheckedMatch), - SYN_IE(TypecheckedHsBinds), SYN_IE(TypecheckedHsExpr) ) -import DsHsSyn ( outPatType, collectTypedPatBinders ) +import {-# SOURCE #-} DsExpr( dsExpr ) +import CmdLineOpts ( DynFlag(..), dopt ) +import HsSyn +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 [ptext SLIT("In") <+> 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 ( allFieldLabelTags, fieldLabelTag ) -import Id ( idType, mkTupleCon, - dataConArgTys, recordSelectorFieldLabel, - GenId{-instance-} - ) -import PprStyle ( PprStyle(..) ) -import PprType ( GenType{-instance-}, GenTyVar{-ditto-} ) -import PrelVals ( pAT_ERROR_ID ) -import Type ( isPrimType, eqTy, getAppDataTyConExpandingDicts, - instantiateTauTy - ) -import TyVar ( GenTyVar{-instance Eq-} ) -import TysPrim ( intPrimTy, charPrimTy, floatPrimTy, doublePrimTy, - addrPrimTy, wordPrimTy - ) -import TysWiredIn ( nilDataCon, consDataCon, mkTupleTy, mkListTy, - charTy, charDataCon, intTy, intDataCon, - floatTy, floatDataCon, doubleTy, - doubleDataCon, stringTy, addrTy, - addrDataCon, wordTy, wordDataCon - ) -import Unique ( Unique{-instance Eq-} ) -import Util ( panic, pprPanic, assertPanic ) +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. @@ -104,7 +192,6 @@ So, the full type signature: \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} @@ -134,7 +221,7 @@ Now {\em unmix} the equations into {\em blocks} [w/ local function 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} @@ -151,34 +238,14 @@ than the Wadler-chapter code for @match@ (p.~93, first @match@ clause). And gluing the ``success expressions'' together isn't quite so pretty. \begin{code} -match [] eqns_info shadows - = pin_eqns eqns_info `thenDs` \ match_result@(MatchResult _ _ _ cxt) -> - - -- 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 - if not (all shadow_can_fail shadows) then - dsShadowError cxt `thenDs` \ _ -> - returnDs match_result - else - returnDs match_result - +match [] eqns_info + = returnDs (foldr1 combineMatchResults match_results) where - pin_eqns [EqnInfo [] match_result] = returnDs match_result - -- Last eqn... can't have pats ... - - pin_eqns (EqnInfo [] match_result1 : more_eqns) - = pin_eqns more_eqns `thenDs` \ match_result2 -> - combineMatchResults match_result1 match_result2 - - pin_eqns other_pat = panic "match: pin_eqns" - - shadow_can_fail :: EquationInfo -> Bool - - shadow_can_fail (EqnInfo [] (MatchResult CanFail _ _ _)) = True - shadow_can_fail (EqnInfo [] (MatchResult CantFail _ _ _)) = False - shadow_can_fail other = panic "match:shadow_can_fail" + match_results = [ ASSERT( null pats) mr + | EqnInfo _ _ pats mr <- eqns_info ] \end{code} + %************************************************************************ %* * %* match: non-empty rule * @@ -198,20 +265,20 @@ Wadler-chapter @match@ (p.~93, last clause), and @match_unmixed_blk@ 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 @@ -219,25 +286,6 @@ match vars@(v:vs) eqns_info shadows 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@ @@ -251,7 +299,10 @@ Replace the `as' pattern @x@@p@ with the pattern p and a binding @x = 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} The result of this tidying is that the column of patterns will include @@ -268,7 +319,7 @@ The @VarPat@ information isn't needed any more after this. 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} @@ -277,30 +328,59 @@ tidyEqnInfo :: Id -> EquationInfo -> DsM EquationInfo -- 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) @@ -317,120 +397,93 @@ tidy1 v (WildPat ty) match_result -} tidy1 v (LazyPat pat) match_result - = mkSelectorBinds [] pat l_to_l (Var v) `thenDs` \ sel_binds -> + = mkSelectorBinds pat (Var v) `thenDs` \ sel_binds -> returnDs (WildPat (idType v), mkCoLetsMatchResult [NonRec b rhs | (b,rhs) <- sel_binds] match_result) - where - l_to_l = binders `zip` binders -- Boring - binders = collectTypedPatBinders pat -- re-express 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` allFieldLabelTags - - -- mk_pat picks a WildPat of the appropriate type for absent fields, - -- and the specified pattern for present fields - mk_pat (arg_ty, tag) = case [pat | (sel_id,pat,_) <- rpats, - fieldLabelTag (recordSelectorFieldLabel sel_id) == tag - ] of - (pat:pats) -> ASSERT( null pats ) - pat - [] -> WildPat arg_ty + tidy_ps = PrefixCon (tidy_con con pat_ty ex_tvs ps) -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 (mkTupleCon 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) -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] - | 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 +-- and everything else goes through unchanged... - mk_addr l@(HsLitLit s) = l +tidy1 v non_interesting_pat match_result + = returnDs (non_interesting_pat, match_result) - mk_float (HsInt i) = HsFloatPrim (fromInteger i) - mk_float (HsFrac f) = HsFloatPrim f - mk_float l@(HsLitLit s) = l - mk_double (HsInt i) = HsDoublePrim (fromInteger i) - mk_double (HsFrac f) = HsDoublePrim f - mk_double l@(HsLitLit s) = l +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: @@ -499,47 +552,86 @@ Presumably just a variant on the constructor case (as it is now). %* 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@ * @@ -585,45 +677,52 @@ Call @match@ with all of this information! \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 False 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 -> 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} %************************************************************************ @@ -638,34 +737,37 @@ pattern. It returns an expression. \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 _) 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} %************************************************************************ @@ -673,45 +775,26 @@ extractMatchResult (MatchResult CanFail result_ty match_fn _) fail_expr %* 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 False 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 -> - returnDs (EqnInfo pats - (MatchResult CantFail (coreExprType core_expr) - (\ ignore -> core_expr) - NoMatchContext)) - -- The NoMatchContext is just a place holder. In a simple match, - -- 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}