Combined grammar changes for binary literals and underscores in literals

[Bruce Chapman]

Joe, Derek et al,

I am just writing up the combined integer literal omnibus proposal.

A couple of questions about this grammar


1)

considering

DecimalNumeral
   0
   NonZeroDigit Digits_opt
   NonZeroDigit Underscores Digits // New   (1)

Underscores
   _
   Underscores _

Digits:
   Digit
   Digit DigitsAndUnderscores_opt Digit (2)


I think we can drop rule (1) above, if rule (2) is changed to

DigitsAndUnderscores_opt Digit

since there is already a leading NonZeroDigit, so we can start a 
"Digits" with an underscore, so we don't need the special rule to allow 
for an underscore immediately after the NonZeroDigit. 

Agreed?

If so we can also make corresponding change for Octal rules then drop 
the Underscores production as these are the only places it is used.


2)

I am wondering whether it would enhance grokkability of we renamed the 
productions

HexDigitsAndUnderscores (and other radix friends, and corresponding singular forms)


to be (eg)
HexMidDigits

because it can't be used at either end of the HexDigits, but can be in 
the middle.

- if we did this the hex rules would change from

HexDigits:
   HexDigit
   HexDigit HexDigitsAndUnderscores_opt HexDigit

HexDigitsAndUnderscores:
   HexDigitOrUnderscore
   HexDigitsAndUnderscores HexDigitOrUnderscore

HexDigitOrUnderscore
   HexDigit
   _



to

HexDigits:
   HexDigit
   HexDigit HexMidDigits_opt HexDigit

HexMidDigits:
   HexMidDigit
   HexMidDigits HexMidDigit  (but actually vice versa as previously 
discussed off-list with Alex Buckley)

HexMidDigit
   HexDigit
   _




Comments?



Bruce






Joe Darcy wrote:
> Hello.
>
> It has been pointed out to me off-list that the grammar as written below 
> would disallow two-digit numbers, which is not desired.  This problem is 
> corrected by changing the productions like
>
>     Digit DigitsAndUnderscores Digit
>
> to be
>
>     Digit DigitsAndUnderscores_opt Digit
>
> -Joe
>
> On 07/15/09 02:22 PM, Joseph D. Darcy wrote:
>   
>> Hello.
>>
>> Getting around to some grammatical hacking, below is a grammar I think 
>> properly captures the desired changes for combining the binary 
>> literals and underscores in literals proposals.  This grammar does 
>> *not* include support for unsigned literals or autosizing literals.
>>
>> The basic approach is to redefine the FooDigits productions to be a 
>> non-empty sequence of Foo digits and underscores starting and ending 
>> with a Foo digit rather than just a non-empty sequence Foo digits.  
>> Each FooDigits nonterminal has two rules, one for a single digit and 
>> one for two or more digits.  The rules for two or more digits force a 
>> true digit, rather than an underscore, as the first and last character.
>>
>> Changing the FooDigits definitions allows underscores in both integer 
>> and floating-point literals.  In more detail:
>>
>> * Replace the productions Digits, HexDigits, OctalDigits, and  in 
>> JLSv3 3.10.1 as shown below
>> * Add productions for BinaryDigits
>> * Add rules for FooDigitsAndUnderscores and FooDigitOrUnderscore
>> * Add productions to DecimalNumeral and OctalNumeral:
>> * Add a rule for Underscores
>>
>> IntegerLiteral:
>>        DecimalIntegerLiteral
>>        HexIntegerLiteral
>>        OctalIntegerLiteral
>>        BinaryIntegerLiteral         // New
>>
>> BinaryIntegerLiteral:
>>        BinaryNumeral IntegerTypeSuffix_opt
>>
>> BinaryNumeral:
>>        0 b BinaryDigits
>>        0 B BinaryDigits
>>
>>
>> DecimalNumeral
>>   0
>>   NonZeroDigit Digits_opt
>>   NonZeroDigit Underscores Digits // New
>>
>> Underscores
>>    _
>>    Underscores _
>>
>> Digits:
>>    Digit
>>    Digit DigitsAndUnderscores Digit
>>
>> DigitsAndUnderscores:
>>    DigitOrUnderscore
>>    DigitsAndUnderscores DigitOrUnderscore
>>
>> DigitOrUnderscore
>>    Digit
>>    _
>>
>>
>> HexDigits:
>>    HexDigit
>>    HexDigit HexDigitsAndUnderscores HexDigit
>>
>> HexDigitsAndUnderscores:
>>    HexDigitOrUnderscore
>>    HexDigitsAndUnderscores HexDigitOrUnderscore
>>
>> HexDigitOrUnderscore
>>    HexDigit
>>    _
>>
>> OctalNumeral:
>>    0 OctalDigits
>>    0 Underscores OctalDigits // New
>>
>> OctalDigits:
>>    OctalDigit
>>    OctalDigit OctalDigitsAndUnderscores OctalDigit
>>
>> OctalDigitsAndUnderscores:
>>    OctalDigitOrUnderscore
>>    OctalDigitsAndUnderscores OctalDigitOrUnderscore
>>
>> OctalDigitOrUnderscore
>>    OctalDigit
>>    _
>>
>> BinaryDigits:
>>    BinaryDigit
>>    BinaryDigit BinaryDigitsAndUnderscores BinaryDigit
>>
>> BinaryDigitsAndUnderscores:
>>    BinaryDigitOrUnderscore
>>    BinaryDigitsAndUnderscores BinaryDigitOrUnderscore
>>
>> BinaryDigitOrUnderscore
>>    BinaryDigit
>>    _
>>
>> BinaryDigit: one of
>>        0 1
>>
>> -Joe
>>     
>
>
>
>