ghc/compiler/basicTypes/BasicTypes.lhs

   1 %
   2 % (c) The GRASP/AQUA Project, Glasgow University, 1997-1998
   3 %
   4 \section[BasicTypes]{Miscellanous types}
   5
   6 This module defines a miscellaneously collection of very simple
   7 types that
   8
   9 \begin{itemize}
  10 \item have no other obvious home
  11 \item don't depend on any other complicated types
  12 \item are used in more than one "part" of the compiler
  13 \end{itemize}
  14
  15 \begin{code}
  16 module BasicTypes(
  17         Version, Arity,
  18         Unused, unused,
  19         Fixity(..), FixityDirection(..),
  20         defaultFixity, maxPrecedence, negateFixity, negatePrecedence,
  21         NewOrData(..),
  22         RecFlag(..), isRec, isNonRec,
  23         TopLevelFlag(..), isTopLevel, isNotTopLevel
  24    ) where
  25
  26 #include "HsVersions.h"
  27
  28 import Outputable
  29 \end{code}
  30
  31 %************************************************************************
  32 %*                                                                      *
  33 \subsection[Unused]{Unused}
  34 %*                                                                      *
  35 %************************************************************************
  36
  37 Used as a placeholder in types.
  38
  39 \begin{code}
  40 type Unused = ()
  41
  42 unused :: Unused
  43 unused = error "Unused is used!"
  44 \end{code}
  45
  46
  47 %************************************************************************
  48 %*                                                                      *
  49 \subsection[Arity]{Arity}
  50 %*                                                                      *
  51 %************************************************************************
  52
  53 \begin{code}
  54 type Arity = Int
  55 \end{code}
  56
  57
  58 %************************************************************************
  59 %*                                                                      *
  60 \subsection[Version]{Module and identifier version numbers}
  61 %*                                                                      *
  62 %************************************************************************
  63
  64 \begin{code}
  65 type Version = Int
  66 \end{code}
  67
  68
  69 %************************************************************************
  70 %*                                                                      *
  71 \subsection[Fixity]{Fixity info}
  72 %*                                                                      *
  73 %************************************************************************
  74
  75 \begin{code}
  76 data Fixity = Fixity Int FixityDirection
  77 data FixityDirection = InfixL | InfixR | InfixN
  78                      deriving(Eq)
  79
  80 instance Outputable Fixity where
  81     ppr (Fixity prec dir) = hcat [ppr dir, space, int prec]
  82
  83 instance Outputable FixityDirection where
  84     ppr InfixL = ptext SLIT("infixl")
  85     ppr InfixR = ptext SLIT("infixr")
  86     ppr InfixN = ptext SLIT("infix")
  87
  88 instance Eq Fixity where                -- Used to determine if two fixities conflict
  89   (Fixity p1 dir1) == (Fixity p2 dir2) = p1==p2 && dir1 == dir2
  90
  91 maxPrecedence = (9::Int)
  92 defaultFixity = Fixity maxPrecedence InfixL
  93
  94 negateFixity :: Fixity
  95 negateFixity     = Fixity negatePrecedence InfixL       -- Precedence of unary negate is wired in as infixl 6!
  96
  97 negatePrecedence :: Int
  98 negatePrecedence = 6
  99 \end{code}
 100
 101
 102 %************************************************************************
 103 %*                                                                      *
 104 \subsection[NewType/DataType]{NewType/DataType flag}
 105 %*                                                                      *
 106 %************************************************************************
 107
 108 \begin{code}
 109 data NewOrData
 110   = NewType     -- "newtype Blah ..."
 111   | DataType    -- "data Blah ..."
 112   | EnumType    -- Enumeration; all constructors are nullary
 113   deriving( Eq )        -- Needed because Demand derives Eq
 114 \end{code}
 115
 116 %************************************************************************
 117 %*                                                                      *
 118 \subsection[Top-level/local]{Top-level/not-top level flag}
 119 %*                                                                      *
 120 %************************************************************************
 121
 122 \begin{code}
 123 data TopLevelFlag
 124   = TopLevel
 125   | NotTopLevel
 126
 127 isTopLevel, isNotTopLevel :: TopLevelFlag -> Bool
 128
 129 isNotTopLevel NotTopLevel = True
 130 isNotTopLevel TopLevel    = False
 131
 132 isTopLevel TopLevel     = True
 133 isTopLevel NotTopLevel  = False
 134 \end{code}
 135
 136 %************************************************************************
 137 %*                                                                      *
 138 \subsection[Recursive/Non-Recursive]{Recursive/Non-Recursive flag}
 139 %*                                                                      *
 140 %************************************************************************
 141
 142 \begin{code}
 143 data RecFlag = Recursive
 144              | NonRecursive
 145
 146 isRec :: RecFlag -> Bool
 147 isRec Recursive    = True
 148 isRec NonRecursive = False
 149
 150 isNonRec :: RecFlag -> Bool
 151 isNonRec Recursive    = False
 152 isNonRec NonRecursive = True
 153 \end{code}