GHC/Lexeme.hs

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  GHC.Lexeme
    -- Copyright   :  (c) The GHC Team
    --
    -- Maintainer  :  ghc-devs@haskell.org
    -- Portability :  portable
    --
    -- Functions to evaluate whether or not a string is a valid identifier.
    --
    module GHC.Lexeme (
              -- * Lexical characteristics of Haskell names
            startsVarSym, startsVarId, startsConSym, startsConId,
            startsVarSymASCII, isVarSymChar, okSymChar
      ) where

    import Data.Char

    -- | Is this character acceptable in a symbol (after the first char)?
    -- See alexGetByte in Lexer.x
    okSymChar :: Char -> Bool
    okSymChar c
      | c `elem` "(),;[]`{}_\"'"
      = False
      | otherwise
      = case generalCategory c of
          ConnectorPunctuation -> True
          DashPunctuation      -> True
          OtherPunctuation     -> True
          MathSymbol           -> True
          CurrencySymbol       -> True
          ModifierSymbol       -> True
          OtherSymbol          -> True
          _                    -> False

    startsVarSym, startsVarId, startsConSym, startsConId :: Char -> Bool
    startsVarSym c = okSymChar c&& c /= ':' -- Infix Ids
    startsConSym c = c == ':'                -- Infix data constructors
    startsVarId c  = c == '_' || case generalCategory c of  -- Ordinary Ids
      LowercaseLetter -> True
      OtherLetter     -> True   -- See #1103
      _               -> False
    startsConId c  = isUpper c || c == '('  -- Ordinary type constructors and data constructors

    startsVarSymASCII :: Char -> Bool
    startsVarSymASCII c = c `elem` "!#$%&*+./<=>?@\\^|~-"

    isVarSymChar :: Char -> Bool
    isVarSymChar c = c == ':' || startsVarSym c