% (c) The GRASP/AQUA Project, Glasgow University, 1997-1998
%
% Author: Juan J. Quintela <quintela@krilin.dc.fi.udc.es>
+\section{Module @Check@ in @deSugar@}
\begin{code}
)
import Id ( idType )
import DataCon ( DataCon, isTupleCon, isUnboxedTupleCon,
- dataConSourceArity )
-import Name ( Name, mkLocalName, getOccName, isConSymOcc, getName, varOcc )
+ dataConSourceArity, dataConFieldLabels )
+import Name ( Name, mkLocalName, getOccName, isDataSymOcc, getName, mkSrcVarOcc )
import Type ( Type,
isUnboxedType,
splitTyConApp_maybe
)
import Unique ( unboundKey )
import TyCon ( tyConDataCons )
+import SrcLoc ( noSrcLoc )
import UniqSet
import Outputable
\end{code}
This module performs checks about if one list of equations are:
- - Overlapped
- - Non exhaustive
-
+\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:
- Two Techniques for Compiling Lazy Pattern Matching
- Luc Maranguet
+\begin{quotation}
+ {\em Two Techniques for Compiling Lazy Pattern Matching},
+ Luc Maranguet,
INRIA Rocquencourt (RR-2385, 1994)
-
-The algorithm is based in the first Technique, but there are some differences:
- - We don't generate code
- - We have constructors and literals (not only literals as in the
+\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)
- - We don't use directions, we must select the columns from
+\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)
+ @Match.lhs@ to generate code)
This function takes the equations of a pattern and returns:
- - The patterns that are not recognized
- - The equations that are not overlapped
-
-It simplify the patterns and then call check' (the same semantics),and it
+\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}
+(more about that in @simplify_eqns@)
-(more about that in simplify_eqns)
-
-We would prefer to have a WarningPat of type String, but Strings and the
+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
+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.
-
- Juan Quintela 5 JUL 1998
+\begin{quotation}
+ Juan Quintela 5 JUL 1998\\
User-friendliness and compiler writers are no friends.
-
+\end{quotation}
\begin{code}
type WarningPat = InPat Name
untidy _ (NegPatIn ipat) = panic "Check.untidy: NegPatIn"
untidy _ (ParPatIn pat) = panic "Check.untidy: ParPatIn"
untidy _ (RecPatIn name fields) = panic "Check.untidy: RecPatIn"
--- [(name, InPat name, Bool)] -- True <=> source used punning
pars :: NeedPars -> WarningPat -> WarningPat
pars True p = ParPatIn p
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.
+@check'@ is called recursively.
There are several cases:
-\begin{item}
+\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
\item In the general case, there can exist literals ,constructors or only
vars in the first column, we actuate in consequence.
-\end{item}
+\end{itemize}
\begin{code}
check' [EqnInfo n ctx ps (MatchResult CanFail _)]
| all_vars ps = ([(take (length ps) (repeat new_wild_pat),[])], unitUniqSet n)
-check' qs@((EqnInfo n ctx ps (MatchResult CanFail _)):_)
+check' qs@((EqnInfo n ctx ps (MatchResult CanFail _)):rs)
| all_vars ps = (pats, addOneToUniqSet indexs n)
where
- (pats,indexs) = check' (tail qs)
+ (pats,indexs) = check' rs
check' qs@((EqnInfo n ctx ps result):_)
| all_vars ps = ([], unitUniqSet n)
| literals = split_by_literals qs
| constructors = split_by_constructor qs
| only_vars = first_column_only_vars qs
- | otherwise = panic "Check.check': Not implemented :-("
+ | otherwise = panic ("Check.check': Not implemented :-(")
where
+ -- Note: RecPats will have been simplified to ConPats
+ -- at this stage.
constructors = or (map is_con qs)
literals = or (map is_lit qs)
+ only_vars = and (map is_var qs)
-- npat = or (map is_npat qs)
-- nplusk = or (map is_nplusk qs)
- only_vars = and (map is_var qs)
\end{code}
Here begins the code to deal with literals, we need to split the matrix
used_lits = get_used_lits qs
\end{code}
-process_explicit_literals is a function that process each literal that appears
+@process_explicit_literals@ is a function that process each literal that appears
in the column of the matrix.
\begin{code}
\end{code}
-Process_literals calls process_explicit_literals to deal with the literals
+@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.
\end{code}
This function splits the equations @qs@ in groups that deal with the
-same constructor
+same constructor.
\begin{code}
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,
+constructors or not explicitly. The reasoning is similar to @process_literals@,
the difference is that here the default case is not always needed.
\begin{code}
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}
\begin{code}
remove_first_column :: TypecheckedPat -- Constructor
where new_var = hash_x
hash_x = mkLocalName unboundKey {- doesn't matter much -}
- (varOcc SLIT("#x"))
+ (mkSrcVarOcc SLIT("#x"))
+ noSrcLoc
make_row_vars_for_constructor :: EquationInfo -> [WarningPat]
make_row_vars_for_constructor (EqnInfo _ _ pats _ ) = take (length (tail pats)) (repeat new_wild_pat)
| otherwise = x : remove_dups xs
get_used_cons :: [EquationInfo] -> [TypecheckedPat]
-get_used_cons qs = remove_dups [con | (EqnInfo _ _ (con@(ConPat _ _ _ _ _):_) _) <- qs]
+get_used_cons qs = remove_dups [con | (EqnInfo _ _ (con@(ConPat _ _ _ _ _):_) _) <- qs ]
remove_dups' :: [HsLit] -> [HsLit]
remove_dups' [] = []
(ConPat _ ty _ _ _) = head used_cons
Just (ty_con,_) = splitTyConApp_maybe ty
all_cons = tyConDataCons ty_con
- used_cons_as_id = map (\ (ConPat id _ _ _ _) -> id) used_cons
- unused_cons = uniqSetToList (mkUniqSet all_cons `minusUniqSet` mkUniqSet used_cons_as_id)
+ used_cons_as_id = map (\ (ConPat d _ _ _ _) -> d) used_cons
+ unused_cons = uniqSetToList
+ (mkUniqSet all_cons `minusUniqSet` mkUniqSet used_cons_as_id)
+
all_vars :: [TypecheckedPat] -> Bool
all_vars [] = True
remove_var :: EquationInfo -> EquationInfo
remove_var (EqnInfo n ctx (WildPat _:ps) result) = EqnInfo n ctx ps result
-remove_var _ = panic "Check:remove_var: equation not begin with a variable"
+remove_var _ =
+ panic "Check.remove_var: equation does not begin with a variable"
is_con :: EquationInfo -> Bool
is_con (EqnInfo _ _ ((ConPat _ _ _ _ _):_) _) = True
-is_con _ = False
+is_con _ = False
is_lit :: EquationInfo -> Bool
is_lit (EqnInfo _ _ ((LitPat _ _):_) _) = True
is_var_lit lit _ = False
\end{code}
-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 geting thir
-argumnts from the list. See where are used for details.
+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.isTupleCon
-
+\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 con't mind the nilDataCon because it doesn't change the way to
-print the messsage, we are searching only for things like: [1,2,3],
-not x:xs ....
+We don't mind the @nilDataCon@ because it doesn't change the way to
+print the messsage, 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 simplify_pat
+In @reconstruct_pat@ we want to ``undo'' the work
+that we have done in @simplify_pat@.
In particular:
- ((,) x y) returns to be (x, y)
- ((:) x xs) returns to be (x:xs)
- (x:(...:[]) returns to be [x,...]
-
+\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 taht we need to use the second case,
-not the second.
-
+contructors until the @[]@ to know that we need to use the second case,
+not the second. \fbox{\ ???\ }
+%
\begin{code}
-
-isInfixCon con = isConSymOcc (getOccName con)
+isInfixCon con = isDataSymOcc (getOccName con)
is_nil (ConPatIn con []) = con == getName nilDataCon
is_nil _ = False
new_wild_pat = WildPatIn
\end{code}
-This equation makes the same thing that tidy in Match.lhs, the
+This equation makes the same thing as @tidy@ in @Match.lhs@, the
difference is that here we can do all the tidy in one place and in the
-Match tidy it must be done one column each time due to bookkeeping
+@Match@ tidy it must be done one column each time due to bookkeeping
constraints.
\begin{code}
simplify_pat (ConPat id ty tvs dicts ps) = ConPat id ty tvs dicts (map simplify_pat ps)
-simplify_pat (ListPat ty ps) = foldr (\ x -> \y -> ConPat consDataCon list_ty [] [] [x, y])
- (ConPat nilDataCon list_ty [] [] [])
- (map simplify_pat ps)
+simplify_pat (ListPat ty ps) = foldr (\ x -> \y -> ConPat consDataCon list_ty [] [] [x, y])
+ (ConPat nilDataCon list_ty [] [] [])
+ (map simplify_pat ps)
where list_ty = mkListTy ty
where
arity = length ps
-simplify_pat (RecPat id ty tvs dicts [])
- = ConPat id ty tvs dicts [wild_pat]
+simplify_pat (RecPat dc ty tvs dicts [])
+ = ConPat dc ty tvs dicts all_wild_pats
where
- wild_pat = WildPat gt
- gt = panic "Check.symplify_pat: gessing gt"
+ all_wild_pats = map (\ _ -> WildPat gt) (dataConFieldLabels dc)
+ gt = panic "Check.symplify_pat{RecPat-1}"
-simplify_pat (RecPat id ty tvs dicts idps)
- = ConPat id ty tvs dicts pats
+simplify_pat (RecPat dc ty tvs dicts idps)
+ = ConPat dc ty tvs dicts pats
where
- pats = map (\ (id,p,_)-> simplify_pat p) idps
+ pats = map (simplify_pat.snd) all_pats
+
+ -- pad out all the missing fields with WildPats.
+ field_pats = map (\ f -> (getName f, WildPat (panic "simplify_pat(RecPat-2)")))
+ (dataConFieldLabels dc)
+ all_pats =
+ foldr
+ ( \ (id,p,_) acc -> insertNm (getName id) p acc)
+ field_pats
+ idps
+
+ insertNm nm p [] = [(nm,p)]
+ insertNm nm p (x@(n,_):xs)
+ | nm == n = (nm,p):xs
+ | otherwise = x : insertNm nm p xs
simplify_pat pat@(LitPat lit lit_ty)
| isUnboxedType lit_ty = pat
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