[Haskell-cafe] Vertical tabs in source code and other obscure chars

Brian Hulley brianh at metamilk.com
Wed Oct 11 07:57:16 EDT 2006

Brian Hulley wrote:
> Hi,
> In the Haskell98 report at
> http://haskell.org/onlinereport/lexemes.html section 2.2 has the rule:
>    whitechar -> newline | vertab | space | tab | uniWhite
> Does anyone know what a vertical tab is supposed to do?
> Is there any reason to allow them as whitespace? (Does anyone in the
> universe actually use them?)

To rephrase my question, what is a Haskell lexer/parser supposed to do when 
it encounters a vertical tab? The description of the layout rule in the 
report does not specify what a vertical tab means.

If no-one knows the answer, perhaps the rule should be changed to:

    whitechar -> newline | space | tab | uniWhite

and a vertical tab's could just be treated as illegal characters.

Regards, Brian.
Logic empowers us and Love gives us purpose.
Yet still phantoms restless for eras long past,
congealed in the present in unthought forms,
strive mightily unseen to destroy us.


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