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Diffstat (limited to 'compiler/deSugar/MatchLit.lhs')
| -rw-r--r-- | compiler/deSugar/MatchLit.lhs | 329 |
1 files changed, 329 insertions, 0 deletions
diff --git a/compiler/deSugar/MatchLit.lhs b/compiler/deSugar/MatchLit.lhs new file mode 100644 index 0000000000..0b7907b22e --- /dev/null +++ b/compiler/deSugar/MatchLit.lhs @@ -0,0 +1,329 @@ +% +% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 +% +\section[MatchLit]{Pattern-matching literal patterns} + +\begin{code} +module MatchLit ( dsLit, dsOverLit, + tidyLitPat, tidyNPat, + matchLiterals, matchNPlusKPats, matchNPats ) where + +#include "HsVersions.h" + +import {-# SOURCE #-} Match ( match ) +import {-# SOURCE #-} DsExpr ( dsExpr ) + +import DsMonad +import DsUtils + +import HsSyn +import Id ( Id, idType ) +import CoreSyn +import TyCon ( tyConDataCons ) +import TcType ( tcSplitTyConApp, isIntegerTy, isIntTy, + isFloatTy, isDoubleTy, isStringTy ) +import Type ( Type ) +import PrelNames ( ratioTyConKey ) +import TysWiredIn ( stringTy, consDataCon, intDataCon, floatDataCon, doubleDataCon ) +import PrelNames ( eqStringName ) +import Unique ( hasKey ) +import Literal ( mkMachInt, Literal(..) ) +import SrcLoc ( noLoc ) +import ListSetOps ( equivClasses, runs ) +import Ratio ( numerator, denominator ) +import SrcLoc ( Located(..) ) +import Outputable +import FastString ( lengthFS, unpackFS ) +\end{code} + +%************************************************************************ +%* * + Desugaring literals + [used to be in DsExpr, but DsMeta needs it, + and it's nice to avoid a loop] +%* * +%************************************************************************ + +We give int/float literals type @Integer@ and @Rational@, respectively. +The typechecker will (presumably) have put \tr{from{Integer,Rational}s} +around them. + +ToDo: put in range checks for when converting ``@i@'' +(or should that be in the typechecker?) + +For numeric literals, we try to detect there use at a standard type +(@Int@, @Float@, etc.) are directly put in the right constructor. +[NB: down with the @App@ conversion.] + +See also below where we look for @DictApps@ for \tr{plusInt}, etc. + +\begin{code} +dsLit :: HsLit -> DsM CoreExpr +dsLit (HsChar c) = returnDs (mkCharExpr c) +dsLit (HsCharPrim c) = returnDs (mkLit (MachChar c)) +dsLit (HsString str) = mkStringExprFS str +dsLit (HsStringPrim s) = returnDs (mkLit (MachStr s)) +dsLit (HsInteger i _) = mkIntegerExpr i +dsLit (HsInt i) = returnDs (mkIntExpr i) +dsLit (HsIntPrim i) = returnDs (mkIntLit i) +dsLit (HsFloatPrim f) = returnDs (mkLit (MachFloat f)) +dsLit (HsDoublePrim d) = returnDs (mkLit (MachDouble d)) + +dsLit (HsRat r ty) + = mkIntegerExpr (numerator r) `thenDs` \ num -> + mkIntegerExpr (denominator r) `thenDs` \ denom -> + returnDs (mkConApp ratio_data_con [Type integer_ty, num, denom]) + where + (ratio_data_con, integer_ty) + = case tcSplitTyConApp ty of + (tycon, [i_ty]) -> ASSERT(isIntegerTy i_ty && tycon `hasKey` ratioTyConKey) + (head (tyConDataCons tycon), i_ty) + +dsOverLit :: HsOverLit Id -> DsM CoreExpr +-- Post-typechecker, the SyntaxExpr field of an OverLit contains +-- (an expression for) the literal value itself +dsOverLit (HsIntegral _ lit) = dsExpr lit +dsOverLit (HsFractional _ lit) = dsExpr lit +\end{code} + +%************************************************************************ +%* * + Tidying lit pats +%* * +%************************************************************************ + +\begin{code} +tidyLitPat :: HsLit -> LPat Id -> LPat Id +-- Result has only the following HsLits: +-- HsIntPrim, HsCharPrim, HsFloatPrim +-- HsDoublePrim, HsStringPrim, HsString +-- * HsInteger, HsRat, HsInt can't show up in LitPats +-- * We get rid of HsChar right here +tidyLitPat (HsChar c) pat = mkCharLitPat c +tidyLitPat (HsString s) pat + | lengthFS s <= 1 -- Short string literals only + = foldr (\c pat -> mkPrefixConPat consDataCon [mkCharLitPat c,pat] stringTy) + (mkNilPat stringTy) (unpackFS s) + -- The stringTy is the type of the whole pattern, not + -- the type to instantiate (:) or [] with! +tidyLitPat lit pat = pat + +---------------- +tidyNPat :: HsOverLit Id -> Maybe (SyntaxExpr Id) -> Type -> LPat Id -> LPat Id +tidyNPat over_lit mb_neg lit_ty default_pat + | isIntTy lit_ty = mk_con_pat intDataCon (HsIntPrim int_val) + | isFloatTy lit_ty = mk_con_pat floatDataCon (HsFloatPrim rat_val) + | isDoubleTy lit_ty = mk_con_pat doubleDataCon (HsDoublePrim rat_val) + | otherwise = default_pat + where + mk_con_pat con lit = mkPrefixConPat con [noLoc $ LitPat lit] lit_ty + neg_lit = case (mb_neg, over_lit) of + (Nothing, _) -> over_lit + (Just _, HsIntegral i s) -> HsIntegral (-i) s + (Just _, HsFractional f s) -> HsFractional (-f) s + + int_val :: Integer + int_val = case neg_lit of + HsIntegral i _ -> i + HsFractional f _ -> panic "tidyNPat" + + rat_val :: Rational + rat_val = case neg_lit of + HsIntegral i _ -> fromInteger i + HsFractional f _ -> f +\end{code} + + +%************************************************************************ +%* * + Pattern matching on LitPat +%* * +%************************************************************************ + +\begin{code} +matchLiterals :: [Id] + -> Type -- Type of the whole case expression + -> [EquationInfo] + -> DsM MatchResult +-- All the EquationInfos have LitPats at the front + +matchLiterals (var:vars) ty eqns + = do { -- Group by literal + let groups :: [[(Literal, EquationInfo)]] + groups = equivClasses cmpTaggedEqn (tagLitEqns eqns) + + -- Deal with each group + ; alts <- mapM match_group groups + + -- Combine results. For everything except String + -- we can use a case expression; for String we need + -- a chain of if-then-else + ; if isStringTy (idType var) then + do { mrs <- mapM wrap_str_guard alts + ; return (foldr1 combineMatchResults mrs) } + else + return (mkCoPrimCaseMatchResult var ty alts) + } + where + match_group :: [(Literal, EquationInfo)] -> DsM (Literal, MatchResult) + match_group group + = do { let (lits, eqns) = unzip group + ; match_result <- match vars ty (shiftEqns eqns) + ; return (head lits, match_result) } + + wrap_str_guard :: (Literal,MatchResult) -> DsM MatchResult + -- Equality check for string literals + wrap_str_guard (MachStr s, mr) + = do { eq_str <- dsLookupGlobalId eqStringName + ; lit <- mkStringExprFS s + ; let pred = mkApps (Var eq_str) [Var var, lit] + ; return (mkGuardedMatchResult pred mr) } +\end{code} + +%************************************************************************ +%* * + Pattern matching on NPat +%* * +%************************************************************************ + +\begin{code} +matchNPats :: [Id] -> Type -> [EquationInfo] -> DsM MatchResult +-- All the EquationInfos have NPat at the front + +matchNPats (var:vars) ty eqns + = do { let groups :: [[(Literal, EquationInfo)]] + groups = equivClasses cmpTaggedEqn (tagLitEqns eqns) + + ; match_results <- mapM (match_group . map snd) groups + + ; ASSERT( not (null match_results) ) + return (foldr1 combineMatchResults match_results) } + where + match_group :: [EquationInfo] -> DsM MatchResult + match_group (eqn1:eqns) + = do { lit_expr <- dsOverLit lit + ; neg_lit <- case mb_neg of + Nothing -> return lit_expr + Just neg -> do { neg_expr <- dsExpr neg + ; return (App neg_expr lit_expr) } + ; eq_expr <- dsExpr eq_chk + ; let pred_expr = mkApps eq_expr [Var var, neg_lit] + ; match_result <- match vars ty (eqn1' : shiftEqns eqns) + ; return (adjustMatchResult (eqn_wrap eqn1) $ + -- Bring the eqn1 wrapper stuff into scope because + -- it may be used in pred_expr + mkGuardedMatchResult pred_expr match_result) } + where + NPat lit mb_neg eq_chk _ : pats1 = eqn_pats eqn1 + eqn1' = eqn1 { eqn_wrap = idWrapper, eqn_pats = pats1 } +\end{code} + + +%************************************************************************ +%* * + Pattern matching on n+k patterns +%* * +%************************************************************************ + +For an n+k pattern, we use the various magic expressions we've been given. +We generate: +\begin{verbatim} + if ge var lit then + let n = sub var lit + in <expr-for-a-successful-match> + else + <try-next-pattern-or-whatever> +\end{verbatim} + +WATCH OUT! Consider + + f (n+1) = ... + f (n+2) = ... + f (n+1) = ... + +We can't group the first and third together, because the second may match +the same thing as the first. Contrast + f 1 = ... + f 2 = ... + f 1 = ... +where we can group the first and third. Hence 'runs' rather than 'equivClasses' + +\begin{code} +matchNPlusKPats all_vars@(var:vars) ty eqns + = do { let groups :: [[(Literal, EquationInfo)]] + groups = runs eqTaggedEqn (tagLitEqns eqns) + + ; match_results <- mapM (match_group . map snd) groups + + ; ASSERT( not (null match_results) ) + return (foldr1 combineMatchResults match_results) } + where + match_group :: [EquationInfo] -> DsM MatchResult + match_group (eqn1:eqns) + = do { ge_expr <- dsExpr ge + ; minus_expr <- dsExpr minus + ; lit_expr <- dsOverLit lit + ; let pred_expr = mkApps ge_expr [Var var, lit_expr] + minusk_expr = mkApps minus_expr [Var var, lit_expr] + ; match_result <- match vars ty (eqn1' : map shift eqns) + ; return (adjustMatchResult (eqn_wrap eqn1) $ + -- Bring the eqn1 wrapper stuff into scope because + -- it may be used in ge_expr, minusk_expr + mkGuardedMatchResult pred_expr $ + mkCoLetMatchResult (NonRec n1 minusk_expr) $ + match_result) } + where + NPlusKPat (L _ n1) lit ge minus : pats1 = eqn_pats eqn1 + eqn1' = eqn1 { eqn_wrap = idWrapper, eqn_pats = pats1 } + + shift eqn@(EqnInfo { eqn_wrap = wrap, + eqn_pats = NPlusKPat (L _ n) _ _ _ : pats }) + = eqn { eqn_wrap = wrap . wrapBind n n1, eqn_pats = pats } +\end{code} + + +%************************************************************************ +%* * + Grouping functions +%* * +%************************************************************************ + +Given a blob of @LitPat@s/@NPat@s, we want to split them into those +that are ``same''/different as one we are looking at. We need to know +whether we're looking at a @LitPat@/@NPat@, and what literal we're after. + +\begin{code} +-- Tag equations by the leading literal +-- NB: we have ordering on Core Literals, but not on HsLits +cmpTaggedEqn :: (Literal,EquationInfo) -> (Literal,EquationInfo) -> Ordering +cmpTaggedEqn (lit1,_) (lit2,_) = lit1 `compare` lit2 + +eqTaggedEqn :: (Literal,EquationInfo) -> (Literal,EquationInfo) -> Bool +eqTaggedEqn (lit1,_) (lit2,_) = lit1 == lit2 + +tagLitEqns :: [EquationInfo] -> [(Literal, EquationInfo)] +tagLitEqns eqns = [(get_lit (firstPat eqn), eqn) | eqn <- eqns] + +get_lit :: Pat Id -> Literal +-- Get a Core literal to use (only) a grouping key +-- Hence its type doesn't need to match the type of the original literal +get_lit (LitPat (HsIntPrim i)) = mkMachInt i +get_lit (LitPat (HsCharPrim c)) = MachChar c +get_lit (LitPat (HsStringPrim s)) = MachStr s +get_lit (LitPat (HsFloatPrim f)) = MachFloat f +get_lit (LitPat (HsDoublePrim d)) = MachDouble d +get_lit (LitPat (HsString s)) = MachStr s + +get_lit (NPat (HsIntegral i _) Nothing _ _) = MachInt i +get_lit (NPat (HsIntegral i _) (Just _) _ _) = MachInt (-i) +get_lit (NPat (HsFractional r _) Nothing _ _) = MachFloat r +get_lit (NPat (HsFractional r _) (Just _) _ _) = MachFloat (-r) + +get_lit (NPlusKPat _ (HsIntegral i _) _ _) = MachInt i + +-- These ones can't happen +-- get_lit (LitPat (HsChar c)) +-- get_lit (LitPat (HsInt i)) +get_lit other = pprPanic "get_lit:bad pattern" (ppr other) +\end{code} + |