[GHC] #9573: Add warning for invalid digits in integer literals

[GHC]

#9573: Add warning for invalid digits in integer literals
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              Reporter:  vlopez      |            Owner:  vlopez
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:  7.10.1
             Component:  Compiler    |          Version:  7.9
  (Parser)                           |         Keywords:  parsing, integer,
            Resolution:              |  octal, binary, hexadecimal,
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Difficult (2-5
       Type of failure:              |  days)
  None/Unknown                       |       Blocked By:
             Test Case:              |  Related Tickets:
              Blocking:              |
Differential Revisions:              |
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Comment (by andreas.abel):

 I think a parse *error* would be more appropriate (and useful) than a
 warning.  I consider it as a bug rather than a feature that the following
 parses:
 {{{
 test h = (+)92837492837h
 }}}
 Whitespace isn't that expensive anymore, and even cheaper on the black
 market ;-), so this "feature" does not seem worth preserving.

 The moral: number literals should have to be terminated by one of the
 following: whitespace, punctuation (including parenthesis), operators etc,
 but not just by an alphabetic character.
 Maybe one can first parse a number literal as it was an identifier (i.e.,
 allow leading numeric characters in identifiers), and then postprocess
 identifiers that start with a numeric character as number literals, giving
 parse errors if they do not make sense.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9573#comment:3>
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