+\begin{code}
+type InPat id = LPat id -- No 'Out' constructors
+type OutPat id = LPat id -- No 'In' constructors
+
+type LPat id = Located (Pat id)
+
+data Pat id
+ = ------------ Simple patterns ---------------
+ WildPat PostTcType -- Wild card
+ | VarPat id -- Variable
+ | VarPatOut id (DictBinds id) -- Used only for overloaded Ids; the
+ -- bindings give its overloaded instances
+ | LazyPat (LPat id) -- Lazy pattern
+ | AsPat (Located id) (LPat id) -- As pattern
+ | ParPat (LPat id) -- Parenthesised pattern
+
+ ------------ Lists, tuples, arrays ---------------
+ | ListPat [LPat id] -- Syntactic list
+ PostTcType -- The type of the elements
+
+ | TuplePat [LPat id] -- Tuple
+ Boxity -- UnitPat is TuplePat []
+
+ | PArrPat [LPat id] -- Syntactic parallel array
+ PostTcType -- The type of the elements
+
+ ------------ Constructor patterns ---------------
+ | ConPatIn (Located id)
+ (HsConDetails id (LPat id))
+
+ | ConPatOut (Located DataCon)
+ [TyVar] -- Existentially bound type variables
+ [id] -- Ditto dictionaries
+ (DictBinds id) -- Bindings involving those dictionaries
+ (HsConDetails id (LPat id))
+ Type -- The type of the pattern
+
+ ------------ Literal and n+k patterns ---------------
+ | LitPat HsLit -- Used for *non-overloaded* literal patterns:
+ -- Int#, Char#, Int, Char, String, etc.
+
+ | NPatIn HsOverLit -- Always positive
+ (Maybe SyntaxName) -- Just (Name of 'negate') for negative
+ -- patterns, Nothing otherwise
+
+ | NPatOut HsLit -- Used for literal patterns where there's an equality function to call
+ -- The literal is retained so that the desugarer can readily identify
+ -- equations with identical literal-patterns
+ -- Always HsInteger, HsRat or HsString.
+ -- *Unlike* NPatIn, for negative literals, the
+ -- literal is acutally negative!
+ Type -- Type of pattern, t
+ (HsExpr id) -- Of type t -> Bool; detects match
+
+ | NPlusKPatIn (Located id) -- n+k pattern
+ HsOverLit -- It'll always be an HsIntegral
+ SyntaxName -- Name of '-' (see RnEnv.lookupSyntaxName)
+
+ | NPlusKPatOut (Located id)
+ Integer
+ (HsExpr id) -- Of type t -> Bool; detects match
+ (HsExpr id) -- Of type t -> t; subtracts k
+
+
+ ------------ Generics ---------------
+ | TypePat (LHsType id) -- Type pattern for generic definitions
+ -- e.g f{| a+b |} = ...
+ -- These show up only in class declarations,
+ -- and should be a top-level pattern
+
+ ------------ Pattern type signatures ---------------
+ | SigPatIn (LPat id) -- Pattern with a type signature
+ (LHsType id)
+
+ | SigPatOut (LPat id) -- Pattern with a type signature
+ Type
+
+ ------------ Dictionary patterns (translation only) ---------------