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
      ) where

    import Data.Char

    startsVarSym, startsVarId, startsConSym, startsConId :: Char -> Bool
    startsVarSym c = startsVarSymASCII c || (ord c > 0x7f && isSymbol 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