2 % (c) The University of Glasgow 2006
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3 % (c) The GRASP/AQUA Project, Glasgow University, 1997-1998
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5 % Author: Juan J. Quintela <quintela@krilin.dc.fi.udc.es>
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8 {-# OPTIONS -fno-warn-incomplete-patterns #-}
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9 -- The above warning supression flag is a temporary kludge.
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10 -- While working on this module you are encouraged to remove it and fix
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11 -- any warnings in the module. See
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12 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
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15 module Check ( check , ExhaustivePat ) where
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17 #include "HsVersions.h"
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30 import Unify( dataConCannotMatch )
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38 This module performs checks about if one list of equations are:
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41 \item Non exhaustive
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43 To discover that we go through the list of equations in a tree-like fashion.
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45 If you like theory, a similar algorithm is described in:
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47 {\em Two Techniques for Compiling Lazy Pattern Matching},
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49 INRIA Rocquencourt (RR-2385, 1994)
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51 The algorithm is based on the first technique, but there are some differences:
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53 \item We don't generate code
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54 \item We have constructors and literals (not only literals as in the
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56 \item We don't use directions, we must select the columns from
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59 (By the way the second technique is really similar to the one used in
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60 @Match.lhs@ to generate code)
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62 This function takes the equations of a pattern and returns:
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64 \item The patterns that are not recognized
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65 \item The equations that are not overlapped
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67 It simplify the patterns and then call @check'@ (the same semantics), and it
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68 needs to reconstruct the patterns again ....
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70 The problem appear with things like:
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75 We want to put the two patterns with the same syntax, (prefix form) and
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76 then all the constructors are equal:
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78 f (: x (: y [])) = ....
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81 (more about that in @tidy_eqns@)
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83 We would prefer to have a @WarningPat@ of type @String@, but Strings and the
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84 Pretty Printer are not friends.
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86 We use @InPat@ in @WarningPat@ instead of @OutPat@
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87 because we need to print the
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88 warning messages in the same way they are introduced, i.e. if the user
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93 He don't want a warning message written:
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95 f (: x (: y [])) ........
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97 Then we need to use InPats.
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99 Juan Quintela 5 JUL 1998\\
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100 User-friendliness and compiler writers are no friends.
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104 type WarningPat = InPat Name
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105 type ExhaustivePat = ([WarningPat], [(Name, [HsLit])])
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107 type EqnSet = UniqSet EqnNo
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110 check :: [EquationInfo] -> ([ExhaustivePat], [EquationInfo])
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111 -- Second result is the shadowed equations
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112 -- if there are view patterns, just give up - don't know what the function is
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113 check qs = pprTrace "check" (ppr tidy_qs) $
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114 (untidy_warns, shadowed_eqns)
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116 tidy_qs = map tidy_eqn qs
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117 (warns, used_nos) = check' ([1..] `zip` tidy_qs)
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118 untidy_warns = map untidy_exhaustive warns
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119 shadowed_eqns = [eqn | (eqn,i) <- qs `zip` [1..],
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120 not (i `elementOfUniqSet` used_nos)]
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122 untidy_exhaustive :: ExhaustivePat -> ExhaustivePat
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123 untidy_exhaustive ([pat], messages) =
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124 ([untidy_no_pars pat], map untidy_message messages)
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125 untidy_exhaustive (pats, messages) =
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126 (map untidy_pars pats, map untidy_message messages)
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128 untidy_message :: (Name, [HsLit]) -> (Name, [HsLit])
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129 untidy_message (string, lits) = (string, map untidy_lit lits)
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132 The function @untidy@ does the reverse work of the @tidy_pat@ funcion.
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136 type NeedPars = Bool
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138 untidy_no_pars :: WarningPat -> WarningPat
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139 untidy_no_pars p = untidy False p
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141 untidy_pars :: WarningPat -> WarningPat
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142 untidy_pars p = untidy True p
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144 untidy :: NeedPars -> WarningPat -> WarningPat
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145 untidy b (L loc p) = L loc (untidy' b p)
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147 untidy' _ p@(WildPat _) = p
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148 untidy' _ p@(VarPat _) = p
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149 untidy' _ (LitPat lit) = LitPat (untidy_lit lit)
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150 untidy' _ p@(ConPatIn _ (PrefixCon [])) = p
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151 untidy' b (ConPatIn name ps) = pars b (L loc (ConPatIn name (untidy_con ps)))
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152 untidy' _ (ListPat pats ty) = ListPat (map untidy_no_pars pats) ty
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153 untidy' _ (TuplePat pats box ty) = TuplePat (map untidy_no_pars pats) box ty
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154 untidy' _ (PArrPat _ _) = panic "Check.untidy: Shouldn't get a parallel array here!"
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155 untidy' _ (SigPatIn _ _) = panic "Check.untidy: SigPat"
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157 untidy_con :: HsConPatDetails Name -> HsConPatDetails Name
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158 untidy_con (PrefixCon pats) = PrefixCon (map untidy_pars pats)
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159 untidy_con (InfixCon p1 p2) = InfixCon (untidy_pars p1) (untidy_pars p2)
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160 untidy_con (RecCon (HsRecFields flds dd))
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161 = RecCon (HsRecFields [ fld { hsRecFieldArg = untidy_pars (hsRecFieldArg fld) }
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162 | fld <- flds ] dd)
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164 pars :: NeedPars -> WarningPat -> Pat Name
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165 pars True p = ParPat p
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168 untidy_lit :: HsLit -> HsLit
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169 untidy_lit (HsCharPrim c) = HsChar c
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170 untidy_lit lit = lit
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173 This equation is the same that check, the only difference is that the
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174 boring work is done, that work needs to be done only once, this is
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175 the reason top have two functions, check is the external interface,
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176 @check'@ is called recursively.
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178 There are several cases:
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181 \item There are no equations: Everything is OK.
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182 \item There are only one equation, that can fail, and all the patterns are
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183 variables. Then that equation is used and the same equation is
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185 \item All the patterns are variables, and the match can fail, there are
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186 more equations then the results is the result of the rest of equations
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187 and this equation is used also.
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189 \item The general case, if all the patterns are variables (here the match
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190 can't fail) then the result is that this equation is used and this
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191 equation doesn't generate non-exhaustive cases.
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193 \item In the general case, there can exist literals ,constructors or only
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194 vars in the first column, we actuate in consequence.
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201 check' :: [(EqnNo, EquationInfo)]
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202 -> ([ExhaustivePat], -- Pattern scheme that might not be matched at all
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203 EqnSet) -- Eqns that are used (others are overlapped)
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205 check' [] = ([([],[])],emptyUniqSet)
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207 check' ((n, EqnInfo { eqn_pats = ps, eqn_rhs = MatchResult can_fail _ }) : rs)
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208 | first_eqn_all_vars && case can_fail of { CantFail -> True; CanFail -> False }
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209 = ([], unitUniqSet n) -- One eqn, which can't fail
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211 | first_eqn_all_vars && null rs -- One eqn, but it can fail
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212 = ([(takeList ps (repeat nlWildPat),[])], unitUniqSet n)
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214 | first_eqn_all_vars -- Several eqns, first can fail
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215 = (pats, addOneToUniqSet indexs n)
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217 first_eqn_all_vars = all_vars ps
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218 (pats,indexs) = check' rs
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221 | some_literals = split_by_literals qs
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222 | some_constructors = split_by_constructor qs
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223 | only_vars = first_column_only_vars qs
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224 | otherwise = pprPanic "Check.check': Not implemented :-(" (ppr first_pats)
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225 -- Shouldn't happen
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227 -- Note: RecPats will have been simplified to ConPats
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229 first_pats = ASSERT2( okGroup qs, pprGroup qs ) map firstPatN qs
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230 some_constructors = any is_con first_pats
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231 some_literals = any is_lit first_pats
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232 only_vars = all is_var first_pats
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235 Here begins the code to deal with literals, we need to split the matrix
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236 in different matrix beginning by each literal and a last matrix with the
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240 split_by_literals :: [(EqnNo, EquationInfo)] -> ([ExhaustivePat], EqnSet)
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241 split_by_literals qs = process_literals used_lits qs
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243 used_lits = get_used_lits qs
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246 @process_explicit_literals@ is a function that process each literal that appears
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247 in the column of the matrix.
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250 process_explicit_literals :: [HsLit] -> [(EqnNo, EquationInfo)] -> ([ExhaustivePat],EqnSet)
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251 process_explicit_literals lits qs = (concat pats, unionManyUniqSets indexs)
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253 pats_indexs = map (\x -> construct_literal_matrix x qs) lits
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254 (pats,indexs) = unzip pats_indexs
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258 @process_literals@ calls @process_explicit_literals@ to deal with the literals
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259 that appears in the matrix and deal also with the rest of the cases. It
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260 must be one Variable to be complete.
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264 process_literals :: [HsLit] -> [(EqnNo, EquationInfo)] -> ([ExhaustivePat],EqnSet)
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265 process_literals used_lits qs
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266 | null default_eqns = ASSERT( not (null qs) ) ([make_row_vars used_lits (head qs)] ++ pats,indexs)
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267 | otherwise = (pats_default,indexs_default)
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269 (pats,indexs) = process_explicit_literals used_lits qs
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270 default_eqns = ASSERT2( okGroup qs, pprGroup qs )
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271 [remove_var q | q <- qs, is_var (firstPatN q)]
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272 (pats',indexs') = check' default_eqns
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273 pats_default = [(nlWildPat:ps,constraints) | (ps,constraints) <- (pats')] ++ pats
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274 indexs_default = unionUniqSets indexs' indexs
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277 Here we have selected the literal and we will select all the equations that
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278 begins for that literal and create a new matrix.
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281 construct_literal_matrix :: HsLit -> [(EqnNo, EquationInfo)] -> ([ExhaustivePat],EqnSet)
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282 construct_literal_matrix lit qs =
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283 (map (\ (xs,ys) -> (new_lit:xs,ys)) pats,indexs)
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285 (pats,indexs) = (check' (remove_first_column_lit lit qs))
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286 new_lit = nlLitPat lit
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288 remove_first_column_lit :: HsLit
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289 -> [(EqnNo, EquationInfo)]
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290 -> [(EqnNo, EquationInfo)]
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291 remove_first_column_lit lit qs
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292 = ASSERT2( okGroup qs, pprGroup qs )
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293 [(n, shift_pat eqn) | q@(n,eqn) <- qs, is_var_lit lit (firstPatN q)]
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295 shift_pat eqn@(EqnInfo { eqn_pats = _:ps}) = eqn { eqn_pats = ps }
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296 shift_pat _ = panic "Check.shift_var: no patterns"
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299 This function splits the equations @qs@ in groups that deal with the
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303 split_by_constructor :: [(EqnNo, EquationInfo)] -> ([ExhaustivePat], EqnSet)
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304 split_by_constructor qs
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305 | notNull unused_cons = need_default_case used_cons unused_cons qs
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306 | otherwise = no_need_default_case used_cons qs
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308 used_cons = get_used_cons qs
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309 unused_cons = get_unused_cons used_cons
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312 The first column of the patterns matrix only have vars, then there is
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316 first_column_only_vars :: [(EqnNo, EquationInfo)] -> ([ExhaustivePat],EqnSet)
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317 first_column_only_vars qs = (map (\ (xs,ys) -> (nlWildPat:xs,ys)) pats,indexs)
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319 (pats, indexs) = check' (map remove_var qs)
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322 This equation takes a matrix of patterns and split the equations by
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323 constructor, using all the constructors that appears in the first column
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324 of the pattern matching.
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326 We can need a default clause or not ...., it depends if we used all the
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327 constructors or not explicitly. The reasoning is similar to @process_literals@,
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328 the difference is that here the default case is not always needed.
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331 no_need_default_case :: [Pat Id] -> [(EqnNo, EquationInfo)] -> ([ExhaustivePat],EqnSet)
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332 no_need_default_case cons qs = (concat pats, unionManyUniqSets indexs)
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334 pats_indexs = map (\x -> construct_matrix x qs) cons
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335 (pats,indexs) = unzip pats_indexs
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337 need_default_case :: [Pat Id] -> [DataCon] -> [(EqnNo, EquationInfo)] -> ([ExhaustivePat],EqnSet)
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338 need_default_case used_cons unused_cons qs
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339 | null default_eqns = (pats_default_no_eqns,indexs)
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340 | otherwise = (pats_default,indexs_default)
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342 (pats,indexs) = no_need_default_case used_cons qs
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343 default_eqns = ASSERT2( okGroup qs, pprGroup qs )
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344 [remove_var q | q <- qs, is_var (firstPatN q)]
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345 (pats',indexs') = check' default_eqns
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346 pats_default = [(make_whole_con c:ps,constraints) |
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347 c <- unused_cons, (ps,constraints) <- pats'] ++ pats
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348 new_wilds = ASSERT( not (null qs) ) make_row_vars_for_constructor (head qs)
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349 pats_default_no_eqns = [(make_whole_con c:new_wilds,[]) | c <- unused_cons] ++ pats
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350 indexs_default = unionUniqSets indexs' indexs
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352 construct_matrix :: Pat Id -> [(EqnNo, EquationInfo)] -> ([ExhaustivePat],EqnSet)
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353 construct_matrix con qs =
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354 (map (make_con con) pats,indexs)
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356 (pats,indexs) = (check' (remove_first_column con qs))
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359 Here remove first column is more difficult that with literals due to the fact
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360 that constructors can have arguments.
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362 For instance, the matrix
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374 remove_first_column :: Pat Id -- Constructor
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375 -> [(EqnNo, EquationInfo)]
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376 -> [(EqnNo, EquationInfo)]
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377 remove_first_column (ConPatOut{ pat_con = L _ con, pat_args = PrefixCon con_pats }) qs
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378 = ASSERT2( okGroup qs, pprGroup qs )
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379 [(n, shift_var eqn) | q@(n, eqn) <- qs, is_var_con con (firstPatN q)]
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381 new_wilds = [WildPat (hsLPatType arg_pat) | arg_pat <- con_pats]
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382 shift_var eqn@(EqnInfo { eqn_pats = ConPatOut{ pat_args = PrefixCon ps' } : ps})
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383 = eqn { eqn_pats = map unLoc ps' ++ ps }
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384 shift_var eqn@(EqnInfo { eqn_pats = WildPat _ : ps })
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385 = eqn { eqn_pats = new_wilds ++ ps }
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386 shift_var _ = panic "Check.Shift_var:No done"
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388 make_row_vars :: [HsLit] -> (EqnNo, EquationInfo) -> ExhaustivePat
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389 make_row_vars used_lits (_, EqnInfo { eqn_pats = pats})
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390 = (nlVarPat new_var:takeList (tail pats) (repeat nlWildPat),[(new_var,used_lits)])
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395 hash_x = mkInternalName unboundKey {- doesn't matter much -}
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396 (mkVarOccFS (fsLit "#x"))
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399 make_row_vars_for_constructor :: (EqnNo, EquationInfo) -> [WarningPat]
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400 make_row_vars_for_constructor (_, EqnInfo { eqn_pats = pats})
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401 = takeList (tail pats) (repeat nlWildPat)
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403 compare_cons :: Pat Id -> Pat Id -> Bool
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404 compare_cons (ConPatOut{ pat_con = L _ id1 }) (ConPatOut { pat_con = L _ id2 }) = id1 == id2
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406 remove_dups :: [Pat Id] -> [Pat Id]
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407 remove_dups [] = []
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408 remove_dups (x:xs) | or (map (\y -> compare_cons x y) xs) = remove_dups xs
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409 | otherwise = x : remove_dups xs
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411 get_used_cons :: [(EqnNo, EquationInfo)] -> [Pat Id]
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412 get_used_cons qs = remove_dups [pat | q <- qs, let pat = firstPatN q,
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415 isConPatOut :: Pat Id -> Bool
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416 isConPatOut (ConPatOut {}) = True
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417 isConPatOut _ = False
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419 remove_dups' :: [HsLit] -> [HsLit]
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420 remove_dups' [] = []
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421 remove_dups' (x:xs) | x `elem` xs = remove_dups' xs
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422 | otherwise = x : remove_dups' xs
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425 get_used_lits :: [(EqnNo, EquationInfo)] -> [HsLit]
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426 get_used_lits qs = remove_dups' all_literals
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428 all_literals = get_used_lits' qs
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430 get_used_lits' :: [(EqnNo, EquationInfo)] -> [HsLit]
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431 get_used_lits' [] = []
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432 get_used_lits' (q:qs)
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433 | Just lit <- get_lit (firstPatN q) = lit : get_used_lits' qs
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434 | otherwise = get_used_lits qs
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436 get_lit :: Pat id -> Maybe HsLit
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437 -- Get a representative HsLit to stand for the OverLit
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438 -- It doesn't matter which one, because they will only be compared
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439 -- with other HsLits gotten in the same way
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440 get_lit (LitPat lit) = Just lit
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441 get_lit (NPat (OverLit { ol_val = HsIntegral i}) mb _) = Just (HsIntPrim (mb_neg mb i))
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442 get_lit (NPat (OverLit { ol_val = HsFractional f }) mb _) = Just (HsFloatPrim (mb_neg mb f))
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443 get_lit (NPat (OverLit { ol_val = HsIsString s }) _ _) = Just (HsStringPrim s)
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444 get_lit _ = Nothing
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446 mb_neg :: Num a => Maybe b -> a -> a
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447 mb_neg Nothing v = v
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448 mb_neg (Just _) v = -v
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450 get_unused_cons :: [Pat Id] -> [DataCon]
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451 get_unused_cons used_cons = ASSERT( not (null used_cons) ) unused_cons
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453 used_set :: UniqSet DataCon
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454 used_set = mkUniqSet [d | ConPatOut{ pat_con = L _ d} <- used_cons]
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455 (ConPatOut { pat_ty = ty }) = head used_cons
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456 Just (ty_con, inst_tys) = splitTyConApp_maybe ty
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457 unused_cons = filterOut is_used (tyConDataCons ty_con)
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458 is_used con = con `elementOfUniqSet` used_set
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459 || dataConCannotMatch inst_tys con
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461 all_vars :: [Pat Id] -> Bool
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463 all_vars (WildPat _:ps) = all_vars ps
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466 remove_var :: (EqnNo, EquationInfo) -> (EqnNo, EquationInfo)
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467 remove_var (n, eqn@(EqnInfo { eqn_pats = WildPat _ : ps})) = (n, eqn { eqn_pats = ps })
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468 remove_var _ = panic "Check.remove_var: equation does not begin with a variable"
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470 -----------------------
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471 eqnPats :: (EqnNo, EquationInfo) -> [Pat Id]
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472 eqnPats (_, eqn) = eqn_pats eqn
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474 okGroup :: [(EqnNo, EquationInfo)] -> Bool
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475 -- True if all equations have at least one pattern, and
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476 -- all have the same number of patterns
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478 okGroup (e:es) = n_pats > 0 && and [length (eqnPats e) == n_pats | e <- es]
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480 n_pats = length (eqnPats e)
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482 -- Half-baked print
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483 pprGroup :: [(EqnNo, EquationInfo)] -> SDoc
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484 pprEqnInfo :: (EqnNo, EquationInfo) -> SDoc
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485 pprGroup es = vcat (map pprEqnInfo es)
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486 pprEqnInfo e = ppr (eqnPats e)
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489 firstPatN :: (EqnNo, EquationInfo) -> Pat Id
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490 firstPatN (_, eqn) = firstPat eqn
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492 is_con :: Pat Id -> Bool
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493 is_con (ConPatOut {}) = True
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496 is_lit :: Pat Id -> Bool
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497 is_lit (LitPat _) = True
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498 is_lit (NPat _ _ _) = True
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501 is_var :: Pat Id -> Bool
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502 is_var (WildPat _) = True
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505 is_var_con :: DataCon -> Pat Id -> Bool
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506 is_var_con _ (WildPat _) = True
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507 is_var_con con (ConPatOut{ pat_con = L _ id }) | id == con = True
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508 is_var_con _ _ = False
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510 is_var_lit :: HsLit -> Pat Id -> Bool
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511 is_var_lit _ (WildPat _) = True
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512 is_var_lit lit pat
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513 | Just lit' <- get_lit pat = lit == lit'
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514 | otherwise = False
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517 The difference beteewn @make_con@ and @make_whole_con@ is that
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518 @make_wole_con@ creates a new constructor with all their arguments, and
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519 @make_con@ takes a list of argumntes, creates the contructor getting their
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520 arguments from the list. See where \fbox{\ ???\ } are used for details.
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522 We need to reconstruct the patterns (make the constructors infix and
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523 similar) at the same time that we create the constructors.
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525 You can tell tuple constructors using
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529 You can see if one constructor is infix with this clearer code :-))))))))))
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531 Lex.isLexConSym (Name.occNameString (Name.getOccName con))
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534 Rather clumsy but it works. (Simon Peyton Jones)
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537 We don't mind the @nilDataCon@ because it doesn't change the way to
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538 print the messsage, we are searching only for things like: @[1,2,3]@,
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541 In @reconstruct_pat@ we want to ``undo'' the work
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542 that we have done in @tidy_pat@.
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544 \begin{tabular}{lll}
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545 @((,) x y)@ & returns to be & @(x, y)@
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546 \\ @((:) x xs)@ & returns to be & @(x:xs)@
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547 \\ @(x:(...:[])@ & returns to be & @[x,...]@
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550 The difficult case is the third one becouse we need to follow all the
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551 contructors until the @[]@ to know that we need to use the second case,
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552 not the second. \fbox{\ ???\ }
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555 isInfixCon :: DataCon -> Bool
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556 isInfixCon con = isDataSymOcc (getOccName con)
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558 is_nil :: Pat Name -> Bool
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559 is_nil (ConPatIn con (PrefixCon [])) = unLoc con == getName nilDataCon
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562 is_list :: Pat Name -> Bool
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563 is_list (ListPat _ _) = True
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566 return_list :: DataCon -> Pat Name -> Bool
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567 return_list id q = id == consDataCon && (is_nil q || is_list q)
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569 make_list :: LPat Name -> Pat Name -> Pat Name
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570 make_list p q | is_nil q = ListPat [p] placeHolderType
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571 make_list p (ListPat ps ty) = ListPat (p:ps) ty
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572 make_list _ _ = panic "Check.make_list: Invalid argument"
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574 make_con :: Pat Id -> ExhaustivePat -> ExhaustivePat
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575 make_con (ConPatOut{ pat_con = L _ id }) (lp:lq:ps, constraints)
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576 | return_list id q = (noLoc (make_list lp q) : ps, constraints)
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577 | isInfixCon id = (nlInfixConPat (getName id) lp lq : ps, constraints)
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578 where q = unLoc lq
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580 make_con (ConPatOut{ pat_con = L _ id, pat_args = PrefixCon pats, pat_ty = ty }) (ps, constraints)
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581 | isTupleTyCon tc = (noLoc (TuplePat pats_con (tupleTyConBoxity tc) ty) : rest_pats, constraints)
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582 | isPArrFakeCon id = (noLoc (PArrPat pats_con placeHolderType) : rest_pats, constraints)
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583 | otherwise = (nlConPat name pats_con : rest_pats, constraints)
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586 (pats_con, rest_pats) = splitAtList pats ps
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587 tc = dataConTyCon id
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589 -- reconstruct parallel array pattern
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591 -- * don't check for the type only; we need to make sure that we are really
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592 -- dealing with one of the fake constructors and not with the real
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595 make_whole_con :: DataCon -> WarningPat
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596 make_whole_con con | isInfixCon con = nlInfixConPat name nlWildPat nlWildPat
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597 | otherwise = nlConPat name pats
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600 pats = [nlWildPat | _ <- dataConOrigArgTys con]
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603 ------------------------------------------------------------------------
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605 ------------------------------------------------------------------------
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607 tidy_eqn does more or less the same thing as @tidy@ in @Match.lhs@;
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608 that is, it removes syntactic sugar, reducing the number of cases that
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609 must be handled by the main checking algorithm. One difference is
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610 that here we can do *all* the tidying at once (recursively), rather
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611 than doing it incrementally.
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614 tidy_eqn :: EquationInfo -> EquationInfo
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615 tidy_eqn eqn = eqn { eqn_pats = map tidy_pat (eqn_pats eqn),
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616 eqn_rhs = tidy_rhs (eqn_rhs eqn) }
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618 -- Horrible hack. The tidy_pat stuff converts "might-fail" patterns to
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619 -- WildPats which of course loses the info that they can fail to match.
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620 -- So we stick in a CanFail as if it were a guard.
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621 tidy_rhs (MatchResult can_fail body)
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622 | any might_fail_pat (eqn_pats eqn) = MatchResult CanFail body
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623 | otherwise = MatchResult can_fail body
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626 might_fail_pat :: Pat Id -> Bool
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627 -- Returns True of patterns that might fail (i.e. fall through) in a way
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628 -- that is not covered by the checking algorithm. Specifically:
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630 -- ViewPat (if refutable)
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632 -- First the two special cases
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633 might_fail_pat (NPlusKPat {}) = True
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634 might_fail_pat (ViewPat _ p _) = not (isIrrefutableHsPat p)
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636 -- Now the recursive stuff
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637 might_fail_pat (ParPat p) = might_fail_lpat p
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638 might_fail_pat (AsPat _ p) = might_fail_lpat p
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639 might_fail_pat (SigPatOut p _ ) = might_fail_lpat p
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640 might_fail_pat (ListPat ps _) = any might_fail_lpat ps
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641 might_fail_pat (TuplePat ps _ _) = any might_fail_lpat ps
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642 might_fail_pat (PArrPat ps _) = any might_fail_lpat ps
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643 might_fail_pat (BangPat p) = might_fail_lpat p
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644 might_fail_pat (ConPatOut { pat_args = ps }) = any might_fail_lpat (hsConPatArgs ps)
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646 -- Finally the ones that are sure to succeed, or which are covered by the checking algorithm
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647 might_fail_pat (LazyPat _) = False -- Always succeeds
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648 might_fail_pat _ = False -- VarPat, WildPat, LitPat, NPat, TypePat
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651 might_fail_lpat :: LPat Id -> Bool
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652 might_fail_lpat (L _ p) = might_fail_pat p
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655 tidy_lpat :: LPat Id -> LPat Id
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656 tidy_lpat p = fmap tidy_pat p
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659 tidy_pat :: Pat Id -> Pat Id
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660 tidy_pat pat@(WildPat _) = pat
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661 tidy_pat (VarPat id) = WildPat (idType id)
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662 tidy_pat (ParPat p) = tidy_pat (unLoc p)
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663 tidy_pat (LazyPat p) = WildPat (hsLPatType p) -- For overlap and exhaustiveness checking
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664 -- purposes, a ~pat is like a wildcard
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665 tidy_pat (BangPat p) = tidy_pat (unLoc p)
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666 tidy_pat (AsPat _ p) = tidy_pat (unLoc p)
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667 tidy_pat (SigPatOut p _) = tidy_pat (unLoc p)
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668 tidy_pat (CoPat _ pat _) = tidy_pat pat
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670 -- These two are might_fail patterns, so we map them to
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671 -- WildPats. The might_fail_pat stuff arranges that the
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672 -- guard says "this equation might fall through".
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673 tidy_pat (NPlusKPat id _ _ _) = WildPat (idType (unLoc id))
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674 tidy_pat (ViewPat _ _ ty) = WildPat ty
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676 tidy_pat pat@(ConPatOut { pat_con = L _ id, pat_args = ps })
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677 = pat { pat_args = tidy_con id ps }
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679 tidy_pat (ListPat ps ty)
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680 = unLoc $ foldr (\ x y -> mkPrefixConPat consDataCon [x,y] list_ty)
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683 where list_ty = mkListTy ty
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685 -- introduce fake parallel array constructors to be able to handle parallel
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686 -- arrays with the existing machinery for constructor pattern
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688 tidy_pat (PArrPat ps ty)
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689 = unLoc $ mkPrefixConPat (parrFakeCon (length ps))
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690 (map tidy_lpat ps)
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693 tidy_pat (TuplePat ps boxity ty)
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694 = unLoc $ mkPrefixConPat (tupleCon boxity arity)
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695 (map tidy_lpat ps) ty
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699 tidy_pat (NPat lit mb_neg eq) = tidyNPat lit mb_neg eq
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701 -- Unpack string patterns fully, so we can see when they overlap with
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702 -- each other, or even explicit lists of Chars.
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703 tidy_pat (LitPat lit)
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704 | HsString s <- lit
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705 = unLoc $ foldr (\c pat -> mkPrefixConPat consDataCon [mk_char_lit c, pat] stringTy)
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706 (mkPrefixConPat nilDataCon [] stringTy) (unpackFS s)
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710 mk_char_lit c = mkPrefixConPat charDataCon [nlLitPat (HsCharPrim c)] charTy
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713 tidy_con :: DataCon -> HsConPatDetails Id -> HsConPatDetails Id
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714 tidy_con _ (PrefixCon ps) = PrefixCon (map tidy_lpat ps)
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715 tidy_con _ (InfixCon p1 p2) = PrefixCon [tidy_lpat p1, tidy_lpat p2]
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716 tidy_con con (RecCon (HsRecFields fs _))
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717 | null fs = PrefixCon [nlWildPat | _ <- dataConOrigArgTys con]
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718 -- Special case for null patterns; maybe not a record at all
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719 | otherwise = PrefixCon (map (tidy_lpat.snd) all_pats)
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721 -- pad out all the missing fields with WildPats.
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722 field_pats = map (\ f -> (f, nlWildPat)) (dataConFieldLabels con)
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723 all_pats = foldr (\(HsRecField id p _) acc -> insertNm (getName (unLoc id)) p acc)
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726 insertNm nm p [] = [(nm,p)]
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727 insertNm nm p (x@(n,_):xs)
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728 | nm == n = (nm,p):xs
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729 | otherwise = x : insertNm nm p xs
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