CurryInfo: base-3.4.0 / Prelude.lex

 
lex :: ReadS String
lex xs = case xs of
  ""                  -> [("", "")]
  (c:cs) | isSpace c  -> lex $ dropWhile isSpace cs
  ('\'':s)            ->
    [('\'' : ch ++ "'", t) | (ch, '\'' : t)  <- lexCharLiteral s, ch /= "'"]
  ('"':s)             -> [('"' : str, t) | (str, t) <- lexString s]
  (c:cs) | isSingle c -> [([c], cs)]
         | isSymbol c -> [(c : sym, t) | (sym, t) <- [span isSymbol cs]]
         | isAlpha c  -> [(c : nam, t) | (nam, t) <- [span isIdChar cs]]
         | isDigit c  -> [ (c : ds ++ fe, t) | (ds, s) <- [span isDigit cs]
                                             , (fe, t) <- lexFracExp s ]
         | otherwise  -> []
 where
  isSingle c = c `elem` ",;()[]{}_`"
  isSymbol c = c `elem` "!@#$%&*+./<=>?\\^|:-~"
  isIdChar c = isAlphaNum c || c `elem` "_'"
  lexFracExp s = case s of
    ('.':c:cs) | isDigit c ->
      [('.' : ds ++ e, u) | (ds, t) <- lexDigits (c : cs), (e, u) <- lexExp t]
    _                      -> lexExp s
  lexExp s = case s of
    (e:cs) | e `elem` "eE" ->
      [ (e : c : ds, u) | (c:t) <- [cs], c `elem` "+-"
                        , (ds, u) <- lexDigits t ] ++
        [(e : ds, t) | (ds, t) <- lexDigits cs]
    _                      -> [("", s)]
  lexString s = case s of
    ('"':cs) -> [("\"", cs)]
    _        -> [ (ch ++ str, u) | (ch, t) <- lexStringItem s
                                  , (str, u) <- lexString t ]
  lexStringItem s = case s of
    ('\\':'&':cs)           -> [("\\&", cs)]
    ('\\':c:cs) | isSpace c -> [("\\&", t) | '\\':t <- [dropWhile isSpace cs]]
    _                       -> lexCharLiteral s

 argument 1

 deterministic operation

 
| Reads a single lexeme from the given string.
Initial white space is discarded and the characters of the lexeme
are returned. If the input string contains only white space,
`lex` returns the empty string as lexeme.
If there is no legal lexeme at the beginning of the input string,
the operation fails, i.e., `[]` is returned.

 _

 referentially transparent operation

 no fixity defined

 {({[]}) |-> {:} || ({:}) |-> _}

 lex

 no precedence defined

 _

 [Char] -> [([Char], [Char])]

 operation might suspend on free variables

 possibly non-terminating

 possibly non-reducible on same data term