2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[MatchLit]{Pattern-matching literal patterns}
7 module MatchLit ( matchLiterals ) where
9 #include "HsVersions.h"
11 import {-# SOURCE #-} Match ( match )
12 import {-# SOURCE #-} DsExpr ( dsExpr )
14 import HsSyn ( HsLit(..), OutPat(..), HsExpr(..) )
15 import CoreSyn ( Expr(..), Bind(..) )
21 import Literal ( mkMachInt, Literal(..) )
22 import Maybes ( catMaybes )
23 import Type ( Type, isUnLiftedType )
24 import Panic ( panic, assertPanic )
33 This first one is a {\em special case} where the literal patterns are
34 unboxed numbers (NB: the fiddling introduced by @tidyEqnInfo@). We
35 want to avoid using the ``equality'' stuff provided by the
36 typechecker, and do a real ``case'' instead. In that sense, the code
37 is much like @matchConFamily@, which uses @match_cons_used@ to create
38 the alts---here we use @match_prims_used@.
41 matchLiterals all_vars@(var:vars) eqns_info@(EqnInfo n ctx (LitPat literal lit_ty : ps1) _ : eqns)
42 = -- GENERATE THE ALTS
43 match_prims_used vars eqns_info `thenDs` \ prim_alts ->
45 -- MAKE THE PRIMITIVE CASE
46 returnDs (mkCoPrimCaseMatchResult var prim_alts)
48 match_prims_used _ [{-no more eqns-}] = returnDs []
50 match_prims_used vars eqns_info@(EqnInfo n ctx ((LitPat literal lit_ty):ps1) _ : eqns)
52 (shifted_eqns_for_this_lit, eqns_not_for_this_lit)
53 = partitionEqnsByLit Nothing literal eqns_info
55 -- recursive call to make other alts...
56 match_prims_used vars eqns_not_for_this_lit `thenDs` \ rest_of_alts ->
58 -- (prim pats have no args; no selectMatchVars as in match_cons_used)
59 -- now do the business to make the alt for _this_ LitPat ...
60 match vars shifted_eqns_for_this_lit `thenDs` \ match_result ->
62 (mk_core_lit lit_ty literal, match_result)
66 mk_core_lit :: Type -> HsLit -> Literal
68 mk_core_lit ty (HsIntPrim i) = mkMachInt i
69 mk_core_lit ty (HsCharPrim c) = MachChar c
70 mk_core_lit ty (HsStringPrim s) = MachStr s
71 mk_core_lit ty (HsFloatPrim f) = MachFloat f
72 mk_core_lit ty (HsDoublePrim d) = MachDouble d
73 mk_core_lit ty (HsLitLit s) = ASSERT(isUnLiftedType ty)
75 mk_core_lit ty other = panic "matchLiterals:mk_core_lit:unhandled"
79 matchLiterals all_vars@(var:vars)
80 eqns_info@(EqnInfo n ctx ((NPat literal lit_ty eq_chk):ps1) _ : eqns)
82 (shifted_eqns_for_this_lit, eqns_not_for_this_lit)
83 = partitionEqnsByLit Nothing literal eqns_info
85 dsExpr (HsApp eq_chk (HsVar var)) `thenDs` \ pred_expr ->
86 match vars shifted_eqns_for_this_lit `thenDs` \ inner_match_result ->
88 match_result1 = mkGuardedMatchResult pred_expr inner_match_result
90 if (null eqns_not_for_this_lit)
92 returnDs match_result1
94 matchLiterals all_vars eqns_not_for_this_lit `thenDs` \ match_result2 ->
95 returnDs (combineMatchResults match_result1 match_result2)
98 For an n+k pattern, we use the various magic expressions we've been given.
103 in <expr-for-a-successful-match>
105 <try-next-pattern-or-whatever>
110 matchLiterals all_vars@(var:vars) eqns_info@(EqnInfo n ctx ((NPlusKPat master_n k ty ge sub):ps1) _ : eqns)
112 (shifted_eqns_for_this_lit, eqns_not_for_this_lit)
113 = partitionEqnsByLit (Just master_n) k eqns_info
115 match vars shifted_eqns_for_this_lit `thenDs` \ inner_match_result ->
117 dsExpr (HsApp ge (HsVar var)) `thenDs` \ ge_expr ->
118 dsExpr (HsApp sub (HsVar var)) `thenDs` \ nminusk_expr ->
121 match_result1 = mkGuardedMatchResult ge_expr $
122 mkCoLetsMatchResult [NonRec master_n nminusk_expr] $
125 if (null eqns_not_for_this_lit)
127 returnDs match_result1
129 matchLiterals all_vars eqns_not_for_this_lit `thenDs` \ match_result2 ->
130 returnDs (combineMatchResults match_result1 match_result2)
133 Given a blob of @LitPat@s/@NPat@s, we want to split them into those
134 that are ``same''/different as one we are looking at. We need to know
135 whether we're looking at a @LitPat@/@NPat@, and what literal we're after.
138 partitionEqnsByLit :: Maybe Id -- (Just v) for N-plus-K patterns, where v
139 -- is the "master" variable;
140 -- Nothing for NPats and LitPats
143 -> ([EquationInfo], -- These ones are for this lit, AND
144 -- they've been "shifted" by stripping
145 -- off the first pattern
146 [EquationInfo] -- These are not for this lit; they
147 -- are exactly as fed in.
150 partitionEqnsByLit nPlusK lit eqns
151 = ( \ (xs,ys) -> (catMaybes xs, catMaybes ys))
152 (unzip (map (partition_eqn nPlusK lit) eqns))
154 partition_eqn :: Maybe Id -> HsLit -> EquationInfo ->
155 (Maybe EquationInfo, Maybe EquationInfo)
157 partition_eqn Nothing lit (EqnInfo n ctx (LitPat k _ : remaining_pats) match_result)
158 | lit `eq_lit` k = (Just (EqnInfo n ctx remaining_pats match_result), Nothing)
159 -- NB the pattern is stripped off the EquationInfo
161 partition_eqn Nothing lit (EqnInfo n ctx (NPat k _ _ : remaining_pats) match_result)
162 | lit `eq_lit` k = (Just (EqnInfo n ctx remaining_pats match_result), Nothing)
163 -- NB the pattern is stripped off the EquationInfo
165 partition_eqn (Just master_n) lit
166 (EqnInfo n ctx (NPlusKPat n' k _ _ _ : remaining_pats) match_result)
167 | lit `eq_lit` k = (Just (EqnInfo n ctx remaining_pats new_match_result), Nothing)
168 -- NB the pattern is stripped off the EquationInfo
170 new_match_result | master_n == n' = match_result
171 | otherwise = mkCoLetsMatchResult
172 [NonRec n' (Var master_n)] match_result
174 -- Wild-card patterns, which will only show up in the shadows,
175 -- go into both groups
176 partition_eqn nPlusK lit
177 eqn@(EqnInfo n ctx (WildPat _ : remaining_pats) match_result)
178 = (Just (EqnInfo n ctx remaining_pats match_result), Just eqn)
180 -- Default case; not for this pattern
181 partition_eqn nPlusK lit eqn = (Nothing, Just eqn)
183 -- ToDo: meditate about this equality business...
185 eq_lit (HsInt i1) (HsInt i2) = i1 == i2
186 eq_lit (HsFrac f1) (HsFrac f2) = f1 == f2
188 eq_lit (HsIntPrim i1) (HsIntPrim i2) = i1 == i2
189 eq_lit (HsFloatPrim f1) (HsFloatPrim f2) = f1 == f2
190 eq_lit (HsDoublePrim d1) (HsDoublePrim d2) = d1 == d2
191 eq_lit (HsChar c1) (HsChar c2) = c1 == c2
192 eq_lit (HsCharPrim c1) (HsCharPrim c2) = c1 == c2
193 eq_lit (HsString s1) (HsString s2) = s1 == s2
194 eq_lit (HsStringPrim s1) (HsStringPrim s2) = s1 == s2
195 eq_lit (HsLitLit s1) (HsLitLit s2) = s1 == s2 -- ToDo: ??? (dubious)
196 eq_lit other1 other2 = panic "matchLiterals:eq_lit"