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   deriving( Eq )        -- Needed because Demand derives Eq
 125 \end{code}
 126
 127 %************************************************************************
 128 %*                                                                      *
 129 \subsection[Top-level/local]{Top-level/not-top level flag}
 130 %*                                                                      *
 131 %************************************************************************
 132
 133 \begin{code}
 134 data TopLevelFlag
 135   = TopLevel
 136   | NotTopLevel
 137
 138 isTopLevel, isNotTopLevel :: TopLevelFlag -> Bool
 139
 140 isNotTopLevel NotTopLevel = True
 141 isNotTopLevel TopLevel    = False
 142
 143 isTopLevel TopLevel     = True
 144 isTopLevel NotTopLevel  = False
 145 \end{code}
 146
 147 %************************************************************************
 148 %*                                                                      *
 149 \subsection[Recursive/Non-Recursive]{Recursive/Non-Recursive flag}
 150 %*                                                                      *
 151 %************************************************************************
 152
 153 \begin{code}
 154 data RecFlag = Recursive
 155              | NonRecursive
 156
 157 isRec :: RecFlag -> Bool
 158 isRec Recursive    = True
 159 isRec NonRecursive = False
 160
 161 isNonRec :: RecFlag -> Bool
 162 isNonRec Recursive    = False
 163 isNonRec NonRecursive = True
 164 \end{code}
 165
 166
 167 %************************************************************************
 168 %*                                                                      *
 169 \subsection{Occurrence information}
 170 %*                                                                      *
 171 %************************************************************************
 172
 173 This data type is used exclusively by the simplifier, but it appears in a
 174 SubstResult, which is currently defined in VarEnv, which is pretty near
 175 the base of the module hierarchy.  So it seemed simpler to put the
 176 defn of OccInfo here, safely at the bottom
 177
 178 \begin{code}
 179 data OccInfo
 180   = NoOccInfo
 181
 182   | IAmDead             -- Marks unused variables.  Sometimes useful for
 183                         -- lambda and case-bound variables.
 184
 185   | OneOcc InsideLam
 186
 187            OneBranch
 188
 189   | IAmALoopBreaker     -- Used by the occurrence analyser to mark loop-breakers
 190                         -- in a group of recursive definitions
 191
 192 seqOccInfo :: OccInfo -> ()
 193 seqOccInfo (OneOcc in_lam once) = in_lam `seq` once `seq` ()
 194 seqOccInfo occ                  = ()
 195
 196 type InsideLam = Bool   -- True <=> Occurs inside a non-linear lambda
 197                         -- Substituting a redex for this occurrence is
 198                         -- dangerous because it might duplicate work.
 199 insideLam    = True
 200 notInsideLam = False
 201
 202 type OneBranch = Bool   -- True <=> Occurs in only one case branch
 203                         --      so no code-duplication issue to worry about
 204 oneBranch    = True
 205 notOneBranch = False
 206
 207 isFragileOccInfo :: OccInfo -> Bool
 208 isFragileOccInfo (OneOcc _ _) = True
 209 isFragileOccInfo other        = False
 210 \end{code}
 211
 212 \begin{code}
 213 instance Outputable OccInfo where
 214   -- only used for debugging; never parsed.  KSW 1999-07
 215   ppr NoOccInfo                                   = empty
 216   ppr IAmALoopBreaker                             = ptext SLIT("_Kx")
 217   ppr IAmDead                                     = ptext SLIT("_Kd")
 218   ppr (OneOcc inside_lam one_branch) | inside_lam = ptext SLIT("_Kl")
 219                                      | one_branch = ptext SLIT("_Ks")
 220                                      | otherwise  = ptext SLIT("_Ks*")
 221
 222 instance Show OccInfo where
 223   showsPrec p occ = showsPrecSDoc p (ppr occ)
 224 \end{code}
 225