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

[GHC]

#9573: Add warning for invalid digits in integer literals
-------------------------------------+-------------------------------------
              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:              |
-------------------------------------+-------------------------------------
Changes (by vlopez):

 * owner:   => vlopez


Old description:

> In its latest version, GHC can parse binary (with `-XBinaryLiterals`),
> octal and hexadecimal literals:
>
> {{{#!hs
> > 0b101010
> > 0o52
> > 0x2A
> }}}
>
> Currently, the parser/lexer reads digits from the input as long as they
> are valid for the specified radix. All subsequent digits are interpreted
> as a new, separate token.
>
> If the user uses a digit which isn't valid for the radix, it may be
> reported with a non-obvious error message, or interpreted in surprising
> ways:
>
> {{{#!hs
> > :t 0o567
> 0o576 :: Num a => a
> > :t 0o5678
> 0o5678 :: (Num (a -> t), Num a) => t
> Prelude> :t 0x1bfah
>
> <interactive>:1:7: Not in scope: ‘h’
> > replicate 0o5678
>  [8,8,8,8,8,8,8...
> }}}
>
> We suggest warning the user when a literal of this sort is written, while
> respecting any other error messages and the original behaviour.
>
> More specifically, the parser or lexer would give a warning if a token
> starting with an alphanumeric character is found immediately after a
> numeric literal, without a blank between them.

New description:

 In its latest version, GHC can parse binary (with `-XBinaryLiterals`),
 octal and hexadecimal literals:

 {{{#!hs
 > 0b101010
 > 0o52
 > 0x2A
 }}}

 Currently, the parser/lexer reads digits from the input as long as they
 are valid for the specified radix. All subsequent digits are interpreted
 as a new, separate token.

 If the user uses a digit which isn't valid for the radix, it may be
 reported with a non-obvious error message, or interpreted in surprising
 ways:

 {{{#!hs
 > :t 0o567
 0o576 :: Num a => a
 > :t 0o5678
 0o5678 :: (Num (a -> t), Num a) => t
 > :t 0x1bfah

 <interactive>:1:7: Not in scope: ‘h’
 > replicate 0o5678
  [8,8,8,8,8,8,8...
 }}}

 We suggest warning the user when a literal of this sort is written, while
 respecting any other error messages and the original behaviour.

 More specifically, the parser or lexer would give a warning if a token
 starting with an alphanumeric character is found immediately after a
 numeric literal, without a blank between them.

--

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9573#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler