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+%
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
+%
+\section[PatSyntax]{Abstract Haskell syntax---patterns}
+
+\begin{code}
+#include "HsVersions.h"
+
+module HsPat (
+ InPat(..),
+ OutPat(..),
+
+ unfailablePats, unfailablePat,
+ patsAreAllCons, isConPat,
+ patsAreAllLits, isLitPat,
+ irrefutablePat,
+ collectPatBinders
+ ) where
+
+import Ubiq
+
+-- friends:
+import HsLit ( HsLit )
+import HsLoop ( HsExpr )
+
+-- others:
+import Id ( GenId, getDataConSig )
+import Maybes ( maybeToBool )
+import Outputable
+import PprStyle ( PprStyle(..) )
+import Pretty
+import TyCon ( maybeTyConSingleCon )
+import TyVar ( GenTyVar )
+import PprType ( GenType, GenTyVar )
+import Unique ( Unique )
+
+\end{code}
+
+Patterns come in distinct before- and after-typechecking flavo(u)rs.
+\begin{code}
+data InPat name
+ = WildPatIn -- wild card
+ | VarPatIn name -- variable
+ | LitPatIn HsLit -- literal
+ | LazyPatIn (InPat name) -- lazy pattern
+ | AsPatIn name -- as pattern
+ (InPat name)
+ | ConPatIn name -- constructed type
+ [InPat name]
+ | ConOpPatIn (InPat name)
+ name
+ (InPat name)
+ | ListPatIn [InPat name] -- syntactic list
+ -- must have >= 1 elements
+ | TuplePatIn [InPat name] -- tuple
+
+ | RecPatIn name -- record
+ [(name, Maybe (InPat name))]
+
+data OutPat tyvar uvar id
+ = WildPat (GenType tyvar uvar) -- wild card
+
+ | VarPat id -- variable (type is in the Id)
+
+ | LazyPat (OutPat tyvar uvar id) -- lazy pattern
+
+ | AsPat id -- as pattern
+ (OutPat tyvar uvar id)
+
+ | ConPat Id -- Constructor is always an Id
+ (GenType tyvar uvar) -- the type of the pattern
+ [(OutPat tyvar uvar id)]
+
+ | ConOpPat (OutPat tyvar uvar id) -- just a special case...
+ Id
+ (OutPat tyvar uvar id)
+ (GenType tyvar uvar)
+ | ListPat -- syntactic list
+ (GenType tyvar uvar) -- the type of the elements
+ [(OutPat tyvar uvar id)]
+
+ | TuplePat [(OutPat tyvar uvar id)] -- tuple
+ -- UnitPat is TuplePat []
+
+ | RecPat id -- record
+ [(id, Maybe (OutPat tyvar uvar id))]
+
+ | LitPat -- Used for *non-overloaded* literal patterns:
+ -- Int#, Char#, Int, Char, String, etc.
+ HsLit
+ (GenType tyvar uvar) -- type of pattern
+
+ | NPat -- Used for *overloaded* literal patterns
+ HsLit -- the literal is retained so that
+ -- the desugarer can readily identify
+ -- equations with identical literal-patterns
+ (GenType tyvar uvar) -- type of pattern, t
+ (HsExpr tyvar uvar id (OutPat tyvar uvar id))
+ -- of type t -> Bool; detects match
+
+ | DictPat -- Used when destructing Dictionaries with an explicit case
+ [id] -- superclass dicts
+ [id] -- methods
+\end{code}
+
+\begin{code}
+instance (Outputable name, NamedThing name) => Outputable (InPat name) where
+ ppr = pprInPat
+
+pprInPat :: (Outputable name, NamedThing name) => PprStyle -> InPat name -> Pretty
+
+pprInPat sty (WildPatIn) = ppStr "_"
+pprInPat sty (VarPatIn var) = pprNonOp sty var
+pprInPat sty (LitPatIn s) = ppr sty s
+pprInPat sty (LazyPatIn pat) = ppBeside (ppChar '~') (ppr sty pat)
+pprInPat sty (AsPatIn name pat)
+ = ppBesides [ppLparen, ppr sty name, ppChar '@', ppr sty pat, ppRparen]
+
+pprInPat sty (ConPatIn c pats)
+ = if null pats then
+ ppr sty c
+ else
+ ppBesides [ppLparen, ppr sty c, ppSP, interppSP sty pats, ppRparen]
+
+
+pprInPat sty (ConOpPatIn pat1 op pat2)
+ = ppBesides [ppLparen, ppr sty pat1, ppSP, ppr sty op, ppSP, ppr sty pat2, ppRparen]
+
+-- ToDo: use pprOp to print op (but this involves fiddling various
+-- contexts & I'm lazy...); *PatIns are *rarely* printed anyway... (WDP)
+
+pprInPat sty (ListPatIn pats)
+ = ppBesides [ppLbrack, interpp'SP sty pats, ppRbrack]
+pprInPat sty (TuplePatIn pats)
+ = ppBesides [ppLparen, interpp'SP sty pats, ppRparen]
+
+pprInPat sty (RecPatIn con rpats)
+ = ppBesides [ppr sty con, ppSP, ppChar '{', ppInterleave ppComma (map pp_rpat rpats), ppChar '}']
+ where
+ pp_rpat (v, Nothing) = ppr sty v
+ pp_rpat (v, Just p) = ppCat [ppr sty v, ppStr "<-", ppr sty p]
+\end{code}
+
+\begin{code}
+instance (Eq tyvar, Outputable tyvar, Eq uvar, Outputable uvar,
+ NamedThing id, Outputable id)
+ => Outputable (OutPat tyvar uvar id) where
+ ppr = pprOutPat
+\end{code}
+
+\begin{code}
+pprOutPat sty (WildPat ty) = ppChar '_'
+pprOutPat sty (VarPat var) = pprNonOp sty var
+pprOutPat sty (LazyPat pat) = ppBesides [ppChar '~', ppr sty pat]
+pprOutPat sty (AsPat name pat)
+ = ppBesides [ppLparen, ppr sty name, ppChar '@', ppr sty pat, ppRparen]
+
+pprOutPat sty (ConPat name ty [])
+ = ppBeside (ppr sty name)
+ (ifPprShowAll sty (pprConPatTy sty ty))
+
+pprOutPat sty (ConPat name ty pats)
+ = ppBesides [ppLparen, ppr sty name, ppSP,
+ interppSP sty pats, ppRparen,
+ ifPprShowAll sty (pprConPatTy sty ty) ]
+
+pprOutPat sty (ConOpPat pat1 op pat2 ty)
+ = ppBesides [ppLparen, ppr sty pat1, ppSP, pprOp sty op, ppSP, ppr sty pat2, ppRparen]
+
+pprOutPat sty (ListPat ty pats)
+ = ppBesides [ppLbrack, interpp'SP sty pats, ppRbrack]
+pprOutPat sty (TuplePat pats)
+ = ppBesides [ppLparen, interpp'SP sty pats, ppRparen]
+
+pprOutPat sty (RecPat con rpats)
+ = ppBesides [ppr sty con, ppChar '{', ppInterleave ppComma (map pp_rpat rpats), ppChar '}']
+ where
+ pp_rpat (v, Nothing) = ppr sty v
+ pp_rpat (v, Just p) = ppBesides [ppr sty v, ppStr "<-", ppr sty p]
+
+pprOutPat sty (LitPat l ty) = ppr sty l -- ToDo: print more
+pprOutPat sty (NPat l ty e) = ppr sty l -- ToDo: print more
+
+pprOutPat sty (DictPat dicts methods)
+ = ppSep [ppBesides [ppLparen, ppPStr SLIT("{-dict-}")],
+ ppBracket (interpp'SP sty dicts),
+ ppBesides [ppBracket (interpp'SP sty methods), ppRparen]]
+
+pprConPatTy sty ty
+ = ppBesides [ppLparen, ppr sty ty, ppRparen]
+\end{code}
+
+%************************************************************************
+%* *
+%* predicates for checking things about pattern-lists in EquationInfo *
+%* *
+%************************************************************************
+\subsection[Pat-list-predicates]{Look for interesting things in patterns}
+
+Unlike in the Wadler chapter, where patterns are either ``variables''
+or ``constructors,'' here we distinguish between:
+\begin{description}
+\item[unfailable:]
+Patterns that cannot fail to match: variables, wildcards, and lazy
+patterns.
+
+These are the irrefutable patterns; the two other categories
+are refutable patterns.
+
+\item[constructor:]
+A non-literal constructor pattern (see next category).
+
+\item[literal patterns:]
+At least the numeric ones may be overloaded.
+\end{description}
+
+A pattern is in {\em exactly one} of the above three categories; `as'
+patterns are treated specially, of course.
+
+\begin{code}
+unfailablePats :: [OutPat a b c] -> Bool
+unfailablePats pat_list = all unfailablePat pat_list
+
+unfailablePat (AsPat _ pat) = unfailablePat pat
+unfailablePat (WildPat _) = True
+unfailablePat (VarPat _) = True
+unfailablePat (LazyPat _) = True
+unfailablePat (DictPat ds ms) = (length ds + length ms) <= 1
+unfailablePat other = False
+
+patsAreAllCons :: [OutPat a b c] -> Bool
+patsAreAllCons pat_list = all isConPat pat_list
+
+isConPat (AsPat _ pat) = isConPat pat
+isConPat (ConPat _ _ _) = True
+isConPat (ConOpPat _ _ _ _) = True
+isConPat (ListPat _ _) = True
+isConPat (TuplePat _) = True
+isConPat (DictPat ds ms) = (length ds + length ms) > 1
+isConPat other = False
+
+patsAreAllLits :: [OutPat a b c] -> Bool
+patsAreAllLits pat_list = all isLitPat pat_list
+
+isLitPat (AsPat _ pat) = isLitPat pat
+isLitPat (LitPat _ _) = True
+isLitPat (NPat _ _ _) = True
+isLitPat other = False
+\end{code}
+
+A pattern is irrefutable if a match on it cannot fail
+(at any depth).
+\begin{code}
+irrefutablePat :: OutPat a b c -> Bool
+
+irrefutablePat (WildPat _) = True
+irrefutablePat (VarPat _) = True
+irrefutablePat (LazyPat _) = True
+irrefutablePat (AsPat _ pat) = irrefutablePat pat
+irrefutablePat (ConPat con tys pats) = all irrefutablePat pats && only_con con
+irrefutablePat (ConOpPat pat1 con pat2 _) = irrefutablePat pat1 && irrefutablePat pat1 && only_con con
+irrefutablePat (ListPat _ _) = False
+irrefutablePat (TuplePat pats) = all irrefutablePat pats
+irrefutablePat (DictPat _ _) = True
+irrefutablePat other_pat = False -- Literals, NPat
+
+only_con con = maybeToBool (maybeTyConSingleCon tycon)
+ where
+ (_,_,_,tycon) = getDataConSig con
+\end{code}
+
+This function @collectPatBinders@ works with the ``collectBinders''
+functions for @HsBinds@, etc. The order in which the binders are
+collected is important; see @HsBinds.lhs@.
+\begin{code}
+collectPatBinders :: InPat a -> [a]
+
+collectPatBinders (VarPatIn var) = [var]
+collectPatBinders (LazyPatIn pat) = collectPatBinders pat
+collectPatBinders (AsPatIn a pat) = a : collectPatBinders pat
+collectPatBinders (ConPatIn c pats) = concat (map collectPatBinders pats)
+collectPatBinders (ConOpPatIn p1 c p2)= collectPatBinders p1 ++ collectPatBinders p2
+collectPatBinders (ListPatIn pats) = concat (map collectPatBinders pats)
+collectPatBinders (TuplePatIn pats) = concat (map collectPatBinders pats)
+collectPatBinders any_other_pat = [ {-no binders-} ]
+\end{code}
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