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 TcHsSyn ( TypecheckedHsExpr, TypecheckedPat )
16 import CoreSyn ( Expr(..), Bind(..) )
22 import Const ( mkMachInt, Literal(..) )
23 import PrimRep ( PrimRep(IntRep) )
24 import Maybes ( catMaybes )
25 import Type ( Type, isUnLiftedType )
26 import Panic ( panic, assertPanic )
35 This first one is a {\em special case} where the literal patterns are
36 unboxed numbers (NB: the fiddling introduced by @tidyEqnInfo@). We
37 want to avoid using the ``equality'' stuff provided by the
38 typechecker, and do a real ``case'' instead. In that sense, the code
39 is much like @matchConFamily@, which uses @match_cons_used@ to create
40 the alts---here we use @match_prims_used@.
43 matchLiterals all_vars@(var:vars) eqns_info@(EqnInfo n ctx (LitPat literal lit_ty : ps1) _ : eqns)
44 = -- GENERATE THE ALTS
45 match_prims_used vars eqns_info `thenDs` \ prim_alts ->
47 -- MAKE THE PRIMITIVE CASE
48 returnDs (mkCoPrimCaseMatchResult var prim_alts)
50 match_prims_used _ [{-no more eqns-}] = returnDs []
52 match_prims_used vars eqns_info@(EqnInfo n ctx ((LitPat literal lit_ty):ps1) _ : eqns)
54 (shifted_eqns_for_this_lit, eqns_not_for_this_lit)
55 = partitionEqnsByLit Nothing literal eqns_info
57 -- recursive call to make other alts...
58 match_prims_used vars eqns_not_for_this_lit `thenDs` \ rest_of_alts ->
60 -- (prim pats have no args; no selectMatchVars as in match_cons_used)
61 -- now do the business to make the alt for _this_ LitPat ...
62 match vars shifted_eqns_for_this_lit `thenDs` \ match_result ->
64 (mk_core_lit lit_ty literal, match_result)
68 mk_core_lit :: Type -> HsLit -> Literal
70 mk_core_lit ty (HsIntPrim i) = mkMachInt i
71 mk_core_lit ty (HsCharPrim c) = MachChar c
72 mk_core_lit ty (HsStringPrim s) = MachStr s
73 mk_core_lit ty (HsFloatPrim f) = MachFloat f
74 mk_core_lit ty (HsDoublePrim d) = MachDouble d
75 mk_core_lit ty (HsLitLit s) = ASSERT(isUnLiftedType ty)
77 mk_core_lit ty other = panic "matchLiterals:mk_core_lit:unhandled"
81 matchLiterals all_vars@(var:vars)
82 eqns_info@(EqnInfo n ctx ((NPat literal lit_ty eq_chk):ps1) _ : eqns)
84 (shifted_eqns_for_this_lit, eqns_not_for_this_lit)
85 = partitionEqnsByLit Nothing literal eqns_info
87 dsExpr (HsApp eq_chk (HsVar var)) `thenDs` \ pred_expr ->
88 match vars shifted_eqns_for_this_lit `thenDs` \ inner_match_result ->
90 match_result1 = mkGuardedMatchResult pred_expr inner_match_result
92 if (null eqns_not_for_this_lit)
94 returnDs match_result1
96 matchLiterals all_vars eqns_not_for_this_lit `thenDs` \ match_result2 ->
97 returnDs (combineMatchResults match_result1 match_result2)
100 For an n+k pattern, we use the various magic expressions we've been given.
105 in <expr-for-a-successful-match>
107 <try-next-pattern-or-whatever>
112 matchLiterals all_vars@(var:vars) eqns_info@(EqnInfo n ctx ((NPlusKPat master_n k ty ge sub):ps1) _ : eqns)
114 (shifted_eqns_for_this_lit, eqns_not_for_this_lit)
115 = partitionEqnsByLit (Just master_n) k eqns_info
117 match vars shifted_eqns_for_this_lit `thenDs` \ inner_match_result ->
119 dsExpr (HsApp ge (HsVar var)) `thenDs` \ ge_expr ->
120 dsExpr (HsApp sub (HsVar var)) `thenDs` \ nminusk_expr ->
123 match_result1 = mkGuardedMatchResult ge_expr $
124 mkCoLetsMatchResult [NonRec master_n nminusk_expr] $
127 if (null eqns_not_for_this_lit)
129 returnDs match_result1
131 matchLiterals all_vars eqns_not_for_this_lit `thenDs` \ match_result2 ->
132 returnDs (combineMatchResults match_result1 match_result2)
135 Given a blob of @LitPat@s/@NPat@s, we want to split them into those
136 that are ``same''/different as one we are looking at. We need to know
137 whether we're looking at a @LitPat@/@NPat@, and what literal we're after.
140 partitionEqnsByLit :: Maybe Id -- (Just v) for N-plus-K patterns, where v
141 -- is the "master" variable;
142 -- Nothing for NPats and LitPats
145 -> ([EquationInfo], -- These ones are for this lit, AND
146 -- they've been "shifted" by stripping
147 -- off the first pattern
148 [EquationInfo] -- These are not for this lit; they
149 -- are exactly as fed in.
152 partitionEqnsByLit nPlusK lit eqns
153 = ( \ (xs,ys) -> (catMaybes xs, catMaybes ys))
154 (unzip (map (partition_eqn nPlusK lit) eqns))
156 partition_eqn :: Maybe Id -> HsLit -> EquationInfo ->
157 (Maybe EquationInfo, Maybe EquationInfo)
159 partition_eqn Nothing lit (EqnInfo n ctx (LitPat k _ : remaining_pats) match_result)
160 | lit `eq_lit` k = (Just (EqnInfo n ctx remaining_pats match_result), Nothing)
161 -- NB the pattern is stripped off the EquationInfo
163 partition_eqn Nothing lit (EqnInfo n ctx (NPat k _ _ : remaining_pats) match_result)
164 | lit `eq_lit` k = (Just (EqnInfo n ctx remaining_pats match_result), Nothing)
165 -- NB the pattern is stripped off the EquationInfo
167 partition_eqn (Just master_n) lit
168 (EqnInfo n ctx (NPlusKPat n' k _ _ _ : remaining_pats) match_result)
169 | lit `eq_lit` k = (Just (EqnInfo n ctx remaining_pats new_match_result), Nothing)
170 -- NB the pattern is stripped off the EquationInfo
172 new_match_result | master_n == n' = match_result
173 | otherwise = mkCoLetsMatchResult
174 [NonRec n' (Var master_n)] match_result
176 -- Wild-card patterns, which will only show up in the shadows,
177 -- go into both groups
178 partition_eqn nPlusK lit
179 eqn@(EqnInfo n ctx (WildPat _ : remaining_pats) match_result)
180 = (Just (EqnInfo n ctx remaining_pats match_result), Just eqn)
182 -- Default case; not for this pattern
183 partition_eqn nPlusK lit eqn = (Nothing, Just eqn)
185 -- ToDo: meditate about this equality business...
187 eq_lit (HsInt i1) (HsInt i2) = i1 == i2
188 eq_lit (HsFrac f1) (HsFrac f2) = f1 == f2
190 eq_lit (HsIntPrim i1) (HsIntPrim i2) = i1 == i2
191 eq_lit (HsFloatPrim f1) (HsFloatPrim f2) = f1 == f2
192 eq_lit (HsDoublePrim d1) (HsDoublePrim d2) = d1 == d2
193 eq_lit (HsChar c1) (HsChar c2) = c1 == c2
194 eq_lit (HsCharPrim c1) (HsCharPrim c2) = c1 == c2
195 eq_lit (HsString s1) (HsString s2) = s1 == s2
196 eq_lit (HsStringPrim s1) (HsStringPrim s2) = s1 == s2
197 eq_lit (HsLitLit s1) (HsLitLit s2) = s1 == s2 -- ToDo: ??? (dubious)
198 eq_lit other1 other2 = panic "matchLiterals:eq_lit"