[Haskell-cafe] Optional EOF in Parsec.

[Antoine Latter]

On Fri, Apr 3, 2009 at 8:17 PM, Kannan Goundan <kannan at cakoose.com> wrote:
>
> I'm writing a parser with Parsec.  In the input language, elements of a sequence
> are separated by commas:
>
>   [1, 2, 3]
>
> However, instead of a comma, you can also use an EOL:
>
>  [1, 2
>  3]
>
> Anywhere else, EOL is considered ignorable whitespace.  So it's not as simple as
> just making EOL a token and looking for (comma | eol).
>

Untested, but hopefully enough so you get an idea of where to start:

> -- End of line parser.  Consumes the carriage return, if present.
> eol :: Parser ()
> eol = eof <|> char '\n'

> -- list-element separator.
> listSep :: Parser ()
> listSep = eol <|> (char ',' >> spaces)

> -- list parser.  The list may be empty - denoted by "[]"
> myListOf :: Parser a -> Parser [a]
> myListOf p =
>      char '[' >>
>      sepBy p listSep >>= \vals ->
>      char ']' >>
>      return vals

This would probably be better off with a custom version of the
'spaces' parser that didn't parse newlines.

Antoine