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,
  18
  19         Arity,
  20
  21         Unused, unused,
  22
  23         Fixity(..), FixityDirection(..),
  24         defaultFixity, maxPrecedence, negateFixity, negatePrecedence,
  25
  26         NewOrData(..),
  27
  28         RecFlag(..), isRec, isNonRec,
  29
  30         TopLevelFlag(..), isTopLevel, isNotTopLevel,
  31
  32         OccInfo(..), seqOccInfo, isFragileOccInfo,
  33         InsideLam, insideLam, notInsideLam,
  34         OneBranch, oneBranch, notOneBranch
  35
  36    ) where
  37
  38 #include "HsVersions.h"
  39
  40 import Outputable
  41 \end{code}
  42
  43 %************************************************************************
  44 %*                                                                      *
  45 \subsection[Unused]{Unused}
  46 %*                                                                      *
  47 %************************************************************************
  48
  49 Used as a placeholder in types.
  50
  51 \begin{code}
  52 type Unused = ()
  53
  54 unused :: Unused
  55 unused = error "Unused is used!"
  56 \end{code}
  57
  58
  59 %************************************************************************
  60 %*                                                                      *
  61 \subsection[Arity]{Arity}
  62 %*                                                                      *
  63 %************************************************************************
  64
  65 \begin{code}
  66 type Arity = Int
  67 \end{code}
  68
  69
  70 %************************************************************************
  71 %*                                                                      *
  72 \subsection[Version]{Module and identifier version numbers}
  73 %*                                                                      *
  74 %************************************************************************
  75
  76 \begin{code}
  77 type Version = Int
  78 \end{code}
  79
  80
  81 %************************************************************************
  82 %*                                                                      *
  83 \subsection[Fixity]{Fixity info}
  84 %*                                                                      *
  85 %************************************************************************
  86
  87 \begin{code}
  88 data Fixity = Fixity Int FixityDirection
  89 data FixityDirection = InfixL | InfixR | InfixN
  90                      deriving(Eq)
  91
  92 instance Outputable Fixity where
  93     ppr (Fixity prec dir) = hcat [ppr dir, space, int prec]
  94
  95 instance Outputable FixityDirection where
  96     ppr InfixL = ptext SLIT("infixl")
  97     ppr InfixR = ptext SLIT("infixr")
  98     ppr InfixN = ptext SLIT("infix")
  99
 100 instance Eq Fixity where                -- Used to determine if two fixities conflict
 101   (Fixity p1 dir1) == (Fixity p2 dir2) = p1==p2 && dir1 == dir2
 102
 103 maxPrecedence = (9::Int)
 104 defaultFixity = Fixity maxPrecedence InfixL
 105
 106 negateFixity :: Fixity
 107 negateFixity     = Fixity negatePrecedence InfixL       -- Precedence of unary negate is wired in as infixl 6!
 108
 109 negatePrecedence :: Int
 110 negatePrecedence = 6
 111 \end{code}
 112
 113
 114 %************************************************************************
 115 %*                                                                      *
 116 \subsection[NewType/DataType]{NewType/DataType flag}
 117 %*                                                                      *
 118 %************************************************************************
 119
 120 \begin{code}
 121 data NewOrData
 122   = NewType     -- "newtype Blah ..."
 123   | DataType    -- "data Blah ..."
 124   | EnumType    -- Enumeration; all constructors are nullary
 125   deriving( Eq )        -- Needed because Demand derives Eq
 126 \end{code}
 127
 128 %************************************************************************
 129 %*                                                                      *
 130 \subsection[Top-level/local]{Top-level/not-top level flag}
 131 %*                                                                      *
 132 %************************************************************************
 133
 134 \begin{code}
 135 data TopLevelFlag
 136   = TopLevel
 137   | NotTopLevel
 138
 139 isTopLevel, isNotTopLevel :: TopLevelFlag -> Bool
 140
 141 isNotTopLevel NotTopLevel = True
 142 isNotTopLevel TopLevel    = False
 143
 144 isTopLevel TopLevel     = True
 145 isTopLevel NotTopLevel  = False
 146 \end{code}
 147
 148 %************************************************************************
 149 %*                                                                      *
 150 \subsection[Recursive/Non-Recursive]{Recursive/Non-Recursive flag}
 151 %*                                                                      *
 152 %************************************************************************
 153
 154 \begin{code}
 155 data RecFlag = Recursive
 156              | NonRecursive
 157
 158 isRec :: RecFlag -> Bool
 159 isRec Recursive    = True
 160 isRec NonRecursive = False
 161
 162 isNonRec :: RecFlag -> Bool
 163 isNonRec Recursive    = False
 164 isNonRec NonRecursive = True
 165 \end{code}
 166
 167
 168 %************************************************************************
 169 %*                                                                      *
 170 \subsection{Occurrence information}
 171 %*                                                                      *
 172 %************************************************************************
 173
 174 This data type is used exclusively by the simplifier, but it appears in a
 175 SubstResult, which is currently defined in VarEnv, which is pretty near
 176 the base of the module hierarchy.  So it seemed simpler to put the
 177 defn of OccInfo here, safely at the bottom
 178
 179 \begin{code}
 180 data OccInfo
 181   = NoOccInfo
 182
 183   | IAmDead             -- Marks unused variables.  Sometimes useful for
 184                         -- lambda and case-bound variables.
 185
 186   | OneOcc InsideLam
 187
 188            OneBranch
 189
 190   | IAmALoopBreaker     -- Used by the occurrence analyser to mark loop-breakers
 191                         -- in a group of recursive definitions
 192
 193 seqOccInfo :: OccInfo -> ()
 194 seqOccInfo (OneOcc in_lam once) = in_lam `seq` once `seq` ()
 195 seqOccInfo occ                  = ()
 196
 197 type InsideLam = Bool   -- True <=> Occurs inside a non-linear lambda
 198                         -- Substituting a redex for this occurrence is
 199                         -- dangerous because it might duplicate work.
 200 insideLam    = True
 201 notInsideLam = False
 202
 203 type OneBranch = Bool   -- True <=> Occurs in only one case branch
 204                         --      so no code-duplication issue to worry about
 205 oneBranch    = True
 206 notOneBranch = False
 207
 208 isFragileOccInfo :: OccInfo -> Bool
 209 isFragileOccInfo (OneOcc _ _) = True
 210 isFragileOccInfo other        = False
 211 \end{code}
 212
 213 \begin{code}
 214 instance Outputable OccInfo where
 215   -- only used for debugging; never parsed.  KSW 1999-07
 216   ppr NoOccInfo                                   = empty
 217   ppr IAmALoopBreaker                             = ptext SLIT("_Kx")
 218   ppr IAmDead                                     = ptext SLIT("_Kd")
 219   ppr (OneOcc inside_lam one_branch) | inside_lam = ptext SLIT("_Kl")
 220                                      | one_branch = ptext SLIT("_Ks")
 221                                      | otherwise  = ptext SLIT("_Ks*")
 222
 223 instance Show OccInfo where
 224   showsPrec p occ = showsPrecSDoc p (ppr occ)
 225 \end{code}
 226