{-
(c) The University of Glasgow 2006
(c) The GRASP/AQUA Project, Glasgow University, 1997-1998

Author: Juan J. Quintela    <quintela@krilin.dc.fi.udc.es>
-}

{-# LANGUAGE CPP #-}

module Check ( check , ExhaustivePat ) where

#include "HsVersions.h"

import HsSyn
import TcHsSyn
import DsUtils
import MatchLit
import Id
import ConLike
import DataCon
import PatSyn
import Name
import TysWiredIn
import PrelNames
import TyCon
import SrcLoc
import UniqSet
import Util
import BasicTypes
import Outputable
import FastString

{-
This module performs checks about if one list of equations are:
\begin{itemize}
\item Overlapped
\item Non exhaustive
\end{itemize}
To discover that we go through the list of equations in a tree-like fashion.

If you like theory, a similar algorithm is described in:
\begin{quotation}
{\em Two Techniques for Compiling Lazy Pattern Matching},
Luc Maranguet,
INRIA Rocquencourt (RR-2385, 1994)
\end{quotation}
The algorithm is based on the first technique, but there are some differences:
\begin{itemize}
\item We don't generate code
\item We have constructors and literals (not only literals as in the
article)
\item We don't use directions, we must select the columns from
left-to-right
\end{itemize}
(By the way the second technique is really similar to the one used in
@Match.lhs@ to generate code)

This function takes the equations of a pattern and returns:
\begin{itemize}
\item The patterns that are not recognized
\item The equations that are not overlapped
\end{itemize}
It simplify the patterns and then call @check'@ (the same semantics), and it
needs to reconstruct the patterns again ....

The problem appear with things like:
\begin{verbatim}
f [x,y]   = ....
f (x:xs)  = .....
\end{verbatim}
We want to put the two patterns with the same syntax, (prefix form) and
then all the constructors are equal:
\begin{verbatim}
f (: x (: y []))   = ....
f (: x xs)         = .....
\end{verbatim}

We would prefer to have a @WarningPat@ of type @String@, but Strings and the
Pretty Printer are not friends.

We use @InPat@ in @WarningPat@ instead of @OutPat@
because we need to print the
warning messages in the same way they are introduced, i.e. if the user
wrote:
\begin{verbatim}
f [x,y] = ..
\end{verbatim}
He don't want a warning message written:
\begin{verbatim}
f (: x (: y [])) ........
\end{verbatim}
Then we need to use InPats.
\begin{quotation}
Juan Quintela 5 JUL 1998\\
User-friendliness and compiler writers are no friends.
\end{quotation}
-}

type WarningPat = InPat Name
type ExhaustivePat = ([WarningPat], [(Name, [HsLit])])
type EqnNo  = Int
type EqnSet = UniqSet EqnNo

check :: [EquationInfo] -> ([ExhaustivePat], [EquationInfo])
-- Second result is the shadowed equations
-- if there are view patterns, just give up - don't know what the function is
where
tidy_qs = map tidy_eqn qs
(warns, used_nos) = check' ([1..] zip tidy_qs)
untidy_warns = map untidy_exhaustive warns
shadowed_eqns = [eqn | (eqn,i) <- qs zip [1..],
not (i elementOfUniqSet used_nos)]

untidy_exhaustive :: ExhaustivePat -> ExhaustivePat
untidy_exhaustive ([pat], messages) =
([untidy_no_pars pat], map untidy_message messages)
untidy_exhaustive (pats, messages) =
(map untidy_pars pats, map untidy_message messages)

untidy_message :: (Name, [HsLit]) -> (Name, [HsLit])
untidy_message (string, lits) = (string, map untidy_lit lits)

-- The function @untidy@ does the reverse work of the @tidy_pat@ function.

type NeedPars = Bool

untidy_no_pars :: WarningPat -> WarningPat
untidy_no_pars p = untidy False p

untidy_pars :: WarningPat -> WarningPat
untidy_pars p = untidy True p

untidy :: NeedPars -> WarningPat -> WarningPat
untidy b (L loc p) = L loc (untidy' b p)
where
untidy' _ p@(WildPat _)          = p
untidy' _ p@(VarPat _)           = p
untidy' _ (LitPat lit)           = LitPat (untidy_lit lit)
untidy' _ p@(ConPatIn _ (PrefixCon [])) = p
untidy' b (ConPatIn name ps)     = pars b (L loc (ConPatIn name (untidy_con ps)))
untidy' _ (ListPat pats ty Nothing)     = ListPat (map untidy_no_pars pats) ty Nothing
untidy' _ (TuplePat pats box tys) = TuplePat (map untidy_no_pars pats) box tys
untidy' _ (ListPat _ _ (Just _)) = panic "Check.untidy: Overloaded ListPat"
untidy' _ (PArrPat _ _)          = panic "Check.untidy: Shouldn't get a parallel array here!"
untidy' _ (SigPatIn _ _)         = panic "Check.untidy: SigPat"
untidy' _ (LazyPat {})           = panic "Check.untidy: LazyPat"
untidy' _ (AsPat {})             = panic "Check.untidy: AsPat"
untidy' _ (ParPat {})            = panic "Check.untidy: ParPat"
untidy' _ (BangPat {})           = panic "Check.untidy: BangPat"
untidy' _ (ConPatOut {})         = panic "Check.untidy: ConPatOut"
untidy' _ (ViewPat {})           = panic "Check.untidy: ViewPat"
untidy' _ (SplicePat {})         = panic "Check.untidy: SplicePat"
untidy' _ (QuasiQuotePat {})     = panic "Check.untidy: QuasiQuotePat"
untidy' _ (NPat {})              = panic "Check.untidy: NPat"
untidy' _ (NPlusKPat {})         = panic "Check.untidy: NPlusKPat"
untidy' _ (SigPatOut {})         = panic "Check.untidy: SigPatOut"
untidy' _ (CoPat {})             = panic "Check.untidy: CoPat"

untidy_con :: HsConPatDetails Name -> HsConPatDetails Name
untidy_con (PrefixCon pats) = PrefixCon (map untidy_pars pats)
untidy_con (InfixCon p1 p2) = InfixCon  (untidy_pars p1) (untidy_pars p2)
untidy_con (RecCon (HsRecFields flds dd))
= RecCon (HsRecFields [ L l (fld { hsRecFieldArg
= untidy_pars (hsRecFieldArg fld) })
| L l fld <- flds ] dd)

pars :: NeedPars -> WarningPat -> Pat Name
pars True p = ParPat p
pars _    p = unLoc p

untidy_lit :: HsLit -> HsLit
untidy_lit (HsCharPrim src c) = HsChar src c
untidy_lit lit                = lit

{-
This equation is the same that check, the only difference is that the
boring work is done, that work needs to be done only once, this is
the reason top have two functions, check is the external interface,
@check'@ is called recursively.

There are several cases:

\begin{itemize}
\item There are no equations: Everything is OK.
\item There are only one equation, that can fail, and all the patterns are
variables. Then that equation is used and the same equation is
non-exhaustive.
\item All the patterns are variables, and the match can fail, there are
more equations then the results is the result of the rest of equations
and this equation is used also.

\item The general case, if all the patterns are variables (here the match
can't fail) then the result is that this equation is used and this
equation doesn't generate non-exhaustive cases.

\item In the general case, there can exist literals ,constructors or only
vars in the first column, we actuate in consequence.

\end{itemize}
-}

check' :: [(EqnNo, EquationInfo)]
-> ([ExhaustivePat],    -- Pattern scheme that might not be matched at all
EqnSet)             -- Eqns that are used (others are overlapped)

check' [] = ([],emptyUniqSet)
-- Was    ([([],[])], emptyUniqSet)
-- But that (a) seems weird, and (b) triggered Trac #7669
-- So now I'm just doing the simple obvious thing

check' ((n, EqnInfo { eqn_pats = ps, eqn_rhs = MatchResult can_fail _ }) : rs)
| first_eqn_all_vars && case can_fail of { CantFail -> True; CanFail -> False }
= ([], unitUniqSet n)        -- One eqn, which can't fail

| first_eqn_all_vars && null rs      -- One eqn, but it can fail
= ([(takeList ps (repeat nlWildPatName),[])], unitUniqSet n)

| first_eqn_all_vars         -- Several eqns, first can fail
where
first_eqn_all_vars = all_vars ps
(pats,indexs) = check' rs

check' qs
| some_literals     = split_by_literals qs
| some_constructors = split_by_constructor qs
| only_vars         = first_column_only_vars qs
| otherwise = pprPanic "Check.check': Not implemented :-(" (ppr first_pats)
-- Shouldn't happen
where
-- Note: RecPats will have been simplified to ConPats
--       at this stage.
first_pats        = ASSERT2( okGroup qs, pprGroup qs ) map firstPatN qs
some_constructors = any is_con first_pats
some_literals     = any is_lit first_pats
only_vars         = all is_var first_pats

{-
Here begins the code to deal with literals, we need to split the matrix
in different matrix beginning by each literal and a last matrix with the
rest of values.
-}

split_by_literals :: [(EqnNo, EquationInfo)] -> ([ExhaustivePat], EqnSet)
split_by_literals qs = process_literals used_lits qs
where
used_lits = get_used_lits qs

{-
@process_explicit_literals@ is a function that process each literal that appears
in the column of the matrix.
-}

process_explicit_literals :: [HsLit] -> [(EqnNo, EquationInfo)] -> ([ExhaustivePat],EqnSet)
process_explicit_literals lits qs = (concat pats, unionManyUniqSets indexs)
where
pats_indexs   = map (\x -> construct_literal_matrix x qs) lits
(pats,indexs) = unzip pats_indexs

{-
@process_literals@ calls @process_explicit_literals@ to deal with the literals
that appears in the matrix and deal also with the rest of the cases. It
must be one Variable to be complete.
-}

process_literals :: [HsLit] -> [(EqnNo, EquationInfo)] -> ([ExhaustivePat],EqnSet)
process_literals used_lits qs
| null default_eqns  = ASSERT( not (null qs) ) ([make_row_vars used_lits (head qs)] ++ pats,indexs)
| otherwise          = (pats_default,indexs_default)
where
(pats,indexs)   = process_explicit_literals used_lits qs
default_eqns    = ASSERT2( okGroup qs, pprGroup qs )
[remove_var q | q <- qs, is_var (firstPatN q)]
(pats',indexs') = check' default_eqns
pats_default    = [(nlWildPatName:ps,constraints) |
(ps,constraints) <- (pats')] ++ pats
indexs_default  = unionUniqSets indexs' indexs

{-
Here we have selected the literal and we will select all the equations that
begins for that literal and create a new matrix.
-}

construct_literal_matrix :: HsLit -> [(EqnNo, EquationInfo)] -> ([ExhaustivePat],EqnSet)
construct_literal_matrix lit qs =
(map (\ (xs,ys) -> (new_lit:xs,ys)) pats,indexs)
where
(pats,indexs) = (check' (remove_first_column_lit lit qs))
new_lit = nlLitPat lit

remove_first_column_lit :: HsLit
-> [(EqnNo, EquationInfo)]
-> [(EqnNo, EquationInfo)]
remove_first_column_lit lit qs
= ASSERT2( okGroup qs, pprGroup qs )
[(n, shift_pat eqn) | q@(n,eqn) <- qs, is_var_lit lit (firstPatN q)]
where
shift_pat eqn@(EqnInfo { eqn_pats = _:ps}) = eqn { eqn_pats = ps }
shift_pat _                                = panic "Check.shift_var: no patterns"

{-
This function splits the equations @qs@ in groups that deal with the
same constructor.
-}

split_by_constructor :: [(EqnNo, EquationInfo)] -> ([ExhaustivePat], EqnSet)
split_by_constructor qs
| null used_cons      = ([], mkUniqSet $map fst qs) | notNull unused_cons = need_default_case used_cons unused_cons qs | otherwise = no_need_default_case used_cons qs where used_cons = get_used_cons qs unused_cons = get_unused_cons used_cons {- The first column of the patterns matrix only have vars, then there is nothing to do. -} first_column_only_vars :: [(EqnNo, EquationInfo)] -> ([ExhaustivePat],EqnSet) first_column_only_vars qs = (map (\ (xs,ys) -> (nlWildPatName:xs,ys)) pats,indexs) where (pats, indexs) = check' (map remove_var qs) {- This equation takes a matrix of patterns and split the equations by constructor, using all the constructors that appears in the first column of the pattern matching. We can need a default clause or not ...., it depends if we used all the constructors or not explicitly. The reasoning is similar to @process_literals@, the difference is that here the default case is not always needed. -} no_need_default_case :: [Pat Id] -> [(EqnNo, EquationInfo)] -> ([ExhaustivePat],EqnSet) no_need_default_case cons qs = (concat pats, unionManyUniqSets indexs) where pats_indexs = map (\x -> construct_matrix x qs) cons (pats,indexs) = unzip pats_indexs need_default_case :: [Pat Id] -> [DataCon] -> [(EqnNo, EquationInfo)] -> ([ExhaustivePat],EqnSet) need_default_case used_cons unused_cons qs | null default_eqns = (pats_default_no_eqns,indexs) | otherwise = (pats_default,indexs_default) where (pats,indexs) = no_need_default_case used_cons qs default_eqns = ASSERT2( okGroup qs, pprGroup qs ) [remove_var q | q <- qs, is_var (firstPatN q)] (pats',indexs') = check' default_eqns pats_default = [(make_whole_con c:ps,constraints) | c <- unused_cons, (ps,constraints) <- pats'] ++ pats new_wilds = ASSERT( not (null qs) ) make_row_vars_for_constructor (head qs) pats_default_no_eqns = [(make_whole_con c:new_wilds,[]) | c <- unused_cons] ++ pats indexs_default = unionUniqSets indexs' indexs construct_matrix :: Pat Id -> [(EqnNo, EquationInfo)] -> ([ExhaustivePat],EqnSet) construct_matrix con qs = (map (make_con con) pats,indexs) where (pats,indexs) = (check' (remove_first_column con qs)) {- Here remove first column is more difficult that with literals due to the fact that constructors can have arguments. For instance, the matrix \begin{verbatim} (: x xs) y z y \end{verbatim} is transformed in: \begin{verbatim} x xs y _ _ y \end{verbatim} -} remove_first_column :: Pat Id -- Constructor -> [(EqnNo, EquationInfo)] -> [(EqnNo, EquationInfo)] remove_first_column (ConPatOut{ pat_con = L _ con, pat_args = PrefixCon con_pats }) qs = ASSERT2( okGroup qs, pprGroup qs ) [(n, shift_var eqn) | q@(n, eqn) <- qs, is_var_con con (firstPatN q)] where new_wilds = [WildPat (hsLPatType arg_pat) | arg_pat <- con_pats] shift_var eqn@(EqnInfo { eqn_pats = ConPatOut{ pat_args = PrefixCon ps' } : ps}) = eqn { eqn_pats = map unLoc ps' ++ ps } shift_var eqn@(EqnInfo { eqn_pats = WildPat _ : ps }) = eqn { eqn_pats = new_wilds ++ ps } shift_var _ = panic "Check.Shift_var:No done" remove_first_column _ _ = panic "Check.remove_first_column: Not ConPatOut" make_row_vars :: [HsLit] -> (EqnNo, EquationInfo) -> ExhaustivePat make_row_vars used_lits (_, EqnInfo { eqn_pats = pats}) = (nlVarPat new_var:takeList (tail pats) (repeat nlWildPatName) ,[(new_var,used_lits)]) where new_var = hash_x hash_x :: Name hash_x = mkInternalName unboundKey {- doesn't matter much -} (mkVarOccFS (fsLit "#x")) noSrcSpan make_row_vars_for_constructor :: (EqnNo, EquationInfo) -> [WarningPat] make_row_vars_for_constructor (_, EqnInfo { eqn_pats = pats}) = takeList (tail pats) (repeat nlWildPatName) compare_cons :: Pat Id -> Pat Id -> Bool compare_cons (ConPatOut{ pat_con = L _ con1 }) (ConPatOut{ pat_con = L _ con2 }) = case (con1, con2) of (RealDataCon id1, RealDataCon id2) -> id1 == id2 _ -> False compare_cons _ _ = panic "Check.compare_cons: Not ConPatOut with RealDataCon" remove_dups :: [Pat Id] -> [Pat Id] remove_dups [] = [] remove_dups (x:xs) | any (\y -> compare_cons x y) xs = remove_dups xs | otherwise = x : remove_dups xs get_used_cons :: [(EqnNo, EquationInfo)] -> [Pat Id] get_used_cons qs = remove_dups [pat | q <- qs, let pat = firstPatN q, isConPatOut pat] isConPatOut :: Pat Id -> Bool isConPatOut ConPatOut{ pat_con = L _ RealDataCon{} } = True isConPatOut _ = False remove_dups' :: [HsLit] -> [HsLit] remove_dups' [] = [] remove_dups' (x:xs) | x elem xs = remove_dups' xs | otherwise = x : remove_dups' xs get_used_lits :: [(EqnNo, EquationInfo)] -> [HsLit] get_used_lits qs = remove_dups' all_literals where all_literals = get_used_lits' qs get_used_lits' :: [(EqnNo, EquationInfo)] -> [HsLit] get_used_lits' [] = [] get_used_lits' (q:qs) | Just lit <- get_lit (firstPatN q) = lit : get_used_lits' qs | otherwise = get_used_lits qs get_lit :: Pat id -> Maybe HsLit -- Get a representative HsLit to stand for the OverLit -- It doesn't matter which one, because they will only be compared -- with other HsLits gotten in the same way get_lit (LitPat lit) = Just lit get_lit (NPat (L _ (OverLit { ol_val = HsIntegral src i})) mb _) = Just (HsIntPrim src (mb_neg negate mb i)) get_lit (NPat (L _ (OverLit { ol_val = HsFractional f })) mb _) = Just (HsFloatPrim (mb_neg negateFractionalLit mb f)) get_lit (NPat (L _ (OverLit { ol_val = HsIsString src s })) _ _) = Just (HsStringPrim src (fastStringToByteString s)) get_lit _ = Nothing mb_neg :: (a -> a) -> Maybe b -> a -> a mb_neg _ Nothing v = v mb_neg negate (Just _) v = negate v get_unused_cons :: [Pat Id] -> [DataCon] get_unused_cons used_cons = ASSERT( not (null used_cons) ) unused_cons where used_set :: UniqSet DataCon used_set = mkUniqSet [d | ConPatOut{ pat_con = L _ (RealDataCon d) } <- used_cons] (ConPatOut { pat_con = L _ (RealDataCon con1), pat_arg_tys = inst_tys }) = head used_cons ty_con = dataConTyCon con1 unused_cons = filterOut is_used (tyConDataCons ty_con) is_used con = con elementOfUniqSet used_set || dataConCannotMatch inst_tys con all_vars :: [Pat Id] -> Bool all_vars [] = True all_vars (WildPat _:ps) = all_vars ps all_vars _ = False remove_var :: (EqnNo, EquationInfo) -> (EqnNo, EquationInfo) remove_var (n, eqn@(EqnInfo { eqn_pats = WildPat _ : ps})) = (n, eqn { eqn_pats = ps }) remove_var _ = panic "Check.remove_var: equation does not begin with a variable" ----------------------- eqnPats :: (EqnNo, EquationInfo) -> [Pat Id] eqnPats (_, eqn) = eqn_pats eqn okGroup :: [(EqnNo, EquationInfo)] -> Bool -- True if all equations have at least one pattern, and -- all have the same number of patterns okGroup [] = True okGroup (e:es) = n_pats > 0 && and [length (eqnPats e) == n_pats | e <- es] where n_pats = length (eqnPats e) -- Half-baked print pprGroup :: [(EqnNo, EquationInfo)] -> SDoc pprEqnInfo :: (EqnNo, EquationInfo) -> SDoc pprGroup es = vcat (map pprEqnInfo es) pprEqnInfo e = ppr (eqnPats e) firstPatN :: (EqnNo, EquationInfo) -> Pat Id firstPatN (_, eqn) = firstPat eqn is_con :: Pat Id -> Bool is_con (ConPatOut {}) = True is_con _ = False is_lit :: Pat Id -> Bool is_lit (LitPat _) = True is_lit (NPat _ _ _) = True is_lit _ = False is_var :: Pat Id -> Bool is_var (WildPat _) = True is_var _ = False is_var_con :: ConLike -> Pat Id -> Bool is_var_con _ (WildPat _) = True is_var_con con (ConPatOut{ pat_con = L _ id }) = id == con is_var_con _ _ = False is_var_lit :: HsLit -> Pat Id -> Bool is_var_lit _ (WildPat _) = True is_var_lit lit pat | Just lit' <- get_lit pat = lit == lit' | otherwise = False {- The difference beteewn @make_con@ and @make_whole_con@ is that @make_wole_con@ creates a new constructor with all their arguments, and @make_con@ takes a list of argumntes, creates the contructor getting their arguments from the list. See where \fbox{\ ???\ } are used for details. We need to reconstruct the patterns (make the constructors infix and similar) at the same time that we create the constructors. You can tell tuple constructors using \begin{verbatim} Id.isTupleDataCon \end{verbatim} You can see if one constructor is infix with this clearer code :-)))))))))) \begin{verbatim} Lex.isLexConSym (Name.occNameString (Name.getOccName con)) \end{verbatim} Rather clumsy but it works. (Simon Peyton Jones) We don't mind the @nilDataCon@ because it doesn't change the way to print the message, we are searching only for things like: @[1,2,3]@, not @x:xs@ .... In @reconstruct_pat@ we want to undo'' the work that we have done in @tidy_pat@. In particular: \begin{tabular}{lll} @((,) x y)@ & returns to be & @(x, y)@ \\ @((:) x xs)@ & returns to be & @(x:xs)@ \\ @(x:(...:[])@ & returns to be & @[x,...]@ \end{tabular} The difficult case is the third one becouse we need to follow all the contructors until the @[]@ to know that we need to use the second case, not the second. \fbox{\ ???\ } -} isInfixCon :: DataCon -> Bool isInfixCon con = isDataSymOcc (getOccName con) is_nil :: Pat Name -> Bool is_nil (ConPatIn con (PrefixCon [])) = unLoc con == getName nilDataCon is_nil _ = False is_list :: Pat Name -> Bool is_list (ListPat _ _ Nothing) = True is_list _ = False return_list :: DataCon -> Pat Name -> Bool return_list id q = id == consDataCon && (is_nil q || is_list q) make_list :: LPat Name -> Pat Name -> Pat Name make_list p q | is_nil q = ListPat [p] placeHolderType Nothing make_list p (ListPat ps ty Nothing) = ListPat (p:ps) ty Nothing make_list _ _ = panic "Check.make_list: Invalid argument" make_con :: Pat Id -> ExhaustivePat -> ExhaustivePat make_con (ConPatOut{ pat_con = L _ (RealDataCon id) }) (lp:lq:ps, constraints) | return_list id q = (noLoc (make_list lp q) : ps, constraints) | isInfixCon id = (nlInfixConPat (getName id) lp lq : ps, constraints) where q = unLoc lq make_con (ConPatOut{ pat_con = L _ (RealDataCon id), pat_args = PrefixCon pats}) (ps, constraints) | isTupleTyCon tc = (noLoc (TuplePat pats_con (tupleTyConBoxity tc) []) : rest_pats, constraints) | isPArrFakeCon id = (noLoc (PArrPat pats_con placeHolderType) : rest_pats, constraints) | otherwise = (nlConPatName name pats_con : rest_pats, constraints) where name = getName id (pats_con, rest_pats) = splitAtList pats ps tc = dataConTyCon id make_con _ _ = panic "Check.make_con: Not ConPatOut" -- reconstruct parallel array pattern -- -- * don't check for the type only; we need to make sure that we are really -- dealing with one of the fake constructors and not with the real -- representation make_whole_con :: DataCon -> WarningPat make_whole_con con | isInfixCon con = nlInfixConPat name nlWildPatName nlWildPatName | otherwise = nlConPatName name pats where name = getName con pats = [nlWildPatName | _ <- dataConOrigArgTys con] {- ------------------------------------------------------------------------ Tidying equations ------------------------------------------------------------------------ tidy_eqn does more or less the same thing as @tidy@ in @Match.lhs@; that is, it removes syntactic sugar, reducing the number of cases that must be handled by the main checking algorithm. One difference is that here we can do *all* the tidying at once (recursively), rather than doing it incrementally. -} tidy_eqn :: EquationInfo -> EquationInfo tidy_eqn eqn = eqn { eqn_pats = map tidy_pat (eqn_pats eqn), eqn_rhs = tidy_rhs (eqn_rhs eqn) } where -- Horrible hack. The tidy_pat stuff converts "might-fail" patterns to -- WildPats which of course loses the info that they can fail to match. -- So we stick in a CanFail as if it were a guard. tidy_rhs (MatchResult can_fail body) | any might_fail_pat (eqn_pats eqn) = MatchResult CanFail body | otherwise = MatchResult can_fail body -------------- might_fail_pat :: Pat Id -> Bool -- Returns True of patterns that might fail (i.e. fall through) in a way -- that is not covered by the checking algorithm. Specifically: -- NPlusKPat -- ViewPat (if refutable) -- ConPatOut of a PatSynCon -- First the two special cases might_fail_pat (NPlusKPat {}) = True might_fail_pat (ViewPat _ p _) = not (isIrrefutableHsPat p) -- Now the recursive stuff might_fail_pat (ParPat p) = might_fail_lpat p might_fail_pat (AsPat _ p) = might_fail_lpat p might_fail_pat (SigPatOut p _ ) = might_fail_lpat p might_fail_pat (ListPat ps _ Nothing) = any might_fail_lpat ps might_fail_pat (ListPat _ _ (Just _)) = True might_fail_pat (TuplePat ps _ _) = any might_fail_lpat ps might_fail_pat (PArrPat ps _) = any might_fail_lpat ps might_fail_pat (BangPat p) = might_fail_lpat p might_fail_pat (ConPatOut { pat_con = con, pat_args = ps }) = case unLoc con of RealDataCon _dcon -> any might_fail_lpat (hsConPatArgs ps) PatSynCon _psyn -> True -- Finally the ones that are sure to succeed, or which are covered by the checking algorithm might_fail_pat (LazyPat _) = False -- Always succeeds might_fail_pat _ = False -- VarPat, WildPat, LitPat, NPat -------------- might_fail_lpat :: LPat Id -> Bool might_fail_lpat (L _ p) = might_fail_pat p -------------- tidy_lpat :: LPat Id -> LPat Id tidy_lpat p = fmap tidy_pat p -------------- tidy_pat :: Pat Id -> Pat Id tidy_pat pat@(WildPat _) = pat tidy_pat (VarPat id) = WildPat (idType id) tidy_pat (ParPat p) = tidy_pat (unLoc p) tidy_pat (LazyPat p) = WildPat (hsLPatType p) -- For overlap and exhaustiveness checking -- purposes, a ~pat is like a wildcard tidy_pat (BangPat p) = tidy_pat (unLoc p) tidy_pat (AsPat _ p) = tidy_pat (unLoc p) tidy_pat (SigPatOut p _) = tidy_pat (unLoc p) tidy_pat (CoPat _ pat _) = tidy_pat pat -- These two are might_fail patterns, so we map them to -- WildPats. The might_fail_pat stuff arranges that the -- guard says "this equation might fall through". tidy_pat (NPlusKPat id _ _ _) = WildPat (idType (unLoc id)) tidy_pat (ViewPat _ _ ty) = WildPat ty tidy_pat (ListPat _ _ (Just (ty,_))) = WildPat ty tidy_pat (ConPatOut { pat_con = L _ (PatSynCon syn), pat_arg_tys = tys }) = WildPat (patSynInstResTy syn tys) tidy_pat pat@(ConPatOut { pat_con = L _ con, pat_args = ps }) = pat { pat_args = tidy_con con ps } tidy_pat (ListPat ps ty Nothing) = unLoc$ foldr (\ x y -> mkPrefixConPat consDataCon [x,y] [ty])
(mkNilPat ty)
(map tidy_lpat ps)

-- introduce fake parallel array constructors to be able to handle parallel
-- arrays with the existing machinery for constructor pattern
--
tidy_pat (PArrPat ps ty)
= unLoc $mkPrefixConPat (parrFakeCon (length ps)) (map tidy_lpat ps) [ty] tidy_pat (TuplePat ps boxity tys) = unLoc$ mkPrefixConPat (tupleCon (boxityNormalTupleSort boxity) arity)
(map tidy_lpat ps) tys
where
arity = length ps

tidy_pat (NPat (L _ lit) mb_neg eq) = tidyNPat tidy_lit_pat lit mb_neg eq
tidy_pat (LitPat lit)         = tidy_lit_pat lit

tidy_pat (ConPatIn {})        = panic "Check.tidy_pat: ConPatIn"
tidy_pat (SplicePat {})       = panic "Check.tidy_pat: SplicePat"
tidy_pat (QuasiQuotePat {})   = panic "Check.tidy_pat: QuasiQuotePat"
tidy_pat (SigPatIn {})        = panic "Check.tidy_pat: SigPatIn"

tidy_lit_pat :: HsLit -> Pat Id
-- Unpack string patterns fully, so we can see when they
-- overlap with each other, or even explicit lists of Chars.
tidy_lit_pat lit
| HsString src s <- lit
= unLoc \$ foldr (\c pat -> mkPrefixConPat consDataCon
[mkCharLitPat src c, pat] [charTy])
(mkPrefixConPat nilDataCon [] [charTy]) (unpackFS s)
| otherwise
= tidyLitPat lit

-----------------
tidy_con :: ConLike -> HsConPatDetails Id -> HsConPatDetails Id
tidy_con _   (PrefixCon ps)   = PrefixCon (map tidy_lpat ps)
tidy_con _   (InfixCon p1 p2) = PrefixCon [tidy_lpat p1, tidy_lpat p2]
tidy_con con (RecCon (HsRecFields fs _))
| null fs   = PrefixCon (replicate arity nlWildPatId)
-- Special case for null patterns; maybe not a record at all
| otherwise = PrefixCon (map (tidy_lpat.snd) all_pats)
where
arity = case con of
RealDataCon dcon -> dataConSourceArity dcon
PatSynCon psyn -> patSynArity psyn

-- pad out all the missing fields with WildPats.
field_pats = case con of
RealDataCon dc -> map (\ f -> (f, nlWildPatId)) (dataConFieldLabels dc)
PatSynCon{}    -> panic "Check.tidy_con: pattern synonym with record syntax"
all_pats = foldr (\(L _ (HsRecField id p _)) acc
-> insertNm (getName (unLoc id)) p acc)
field_pats fs

insertNm nm p [] = [(nm,p)]
insertNm nm p (x@(n,_):xs)
| nm == n    = (nm,p):xs
| otherwise  = x : insertNm nm p xs