JShell: result truncation

[Robert Field]

On 09/22/16 17:18, Jonathan Gibbons wrote:
> Robert,
>
> Thanks for the update.  Making the truncation only work on strings 
> seems reasonable.  But (given we're dealing with strings) it might 
> still be nice to see if there is some whitespace or punctuation near 
> the truncation point. Or would that be "too clever for its own good"?

Probably ;-)

>
> In a very separate context, jtreg uses the algorithm of a max string 
> length, and then in the case of a long string, it shows 2/3 of that 
> amount from the beginning of the string, and the remaining 1/3 of that 
> amount from the end of the string.

I've created:
    https://bugs.openjdk.java.net/browse/JDK-8166637

Thanks,
Robert

>
> -- Jon
>
>
> On 09/22/2016 04:47 PM, Robert Field wrote:
>> [Was: Re: JShell: representation of array values]
>>
>> John, Jon,
>>
>> Thanks for the comments.  Some context is needed.  This is the JShell 
>> stack (a prettier, more detailed view attached):
>>
>>    jshell tool
>>    -- JShell API --
>>    JShell core implementation
>>    -- JShell SPI --
>>    JShell execution engine
>>
>> Returned execution values, through both interfaces, and thus in the 
>> core implementation and tool are Strings.
>> The execution engine is charged with translating returned values into 
>> a String representation.  This is where the work to provide a better 
>> representation of arrays was done.
>> No truncation is done (for any kind of value) at the execution engine 
>> level.
>>
>> Truncation is done only in the tool.   And it is configurable. See 
>> /help output below.
>>
>> I don't want to push configurable truncation through all those 
>> layers.  So, we are stuck with truncation being stupid (not in terms 
>> of context) in terms of the kind of value it is truncating.
>> Truncation is operating on Strings for which it knows nothing of 
>> their structure or content.
>> They might be a long String, List, or ...
>>
>> That said, it better for whatever the truncated thing is to have a 
>> bit of terminal context.
>>
>> A String:
>>
>>        "abcdefg ... xyz"
>>
>> A List:
>>
>>        [1, 2, 3, 4, ... 999]
>>
>> An array:
>>
>>        boolean[233] { false, false, false, false, f ... se }
>>
>> So, there could be a length of termination context argument.
>>
>> -Robert
>>
>>
>> jshell> /help /set truncation
>> |  Set the max length a displayed value.
>> |
>> |       /set truncation <mode> <length> <selector>...
>> |
>> |  Where <mode> is the name of a previously defined feedback mode -- 
>> see '/help /set mode'.
>> |  Where <length> is an unsigned integer representing a maximum length.
>> |  Where <selector> is only needed if you wish to fine-tune value 
>> truncation length
>> |  by context, <selector> is the context in which the truncation is 
>> applied.
>> |  The structure of selector is a hyphen separated list of selector 
>> kind lists.
>> |  A selector kind list is a comma separated list of values of one 
>> selector kind.
>> |  A selector matches if each selector kind list matches; A selector 
>> kind list
>> |  matches if one of the values matches.
>> |
>> |  Below are the relevant selector kinds for truncation.
>> |
>> |  The case selector kind describes the kind of snippet.  The values 
>> are:
>> |       vardecl    -- variable declaration without init
>> |       varinit    -- variable declaration with init
>> |       expression -- expression -- note: {name}==scratch-variable-name
>> |       varvalue   -- variable value expression
>> |       assignment -- assign variable
>> |       The action selector kind describes what happened to the 
>> snippet.  The values are:
>> |       added     -- snippet has been added
>> |       modified  -- an existing snippet has been modified
>> |       replaced  -- an existing snippet has been replaced with a new 
>> snippet
>> |  Examples:
>> |       /set trunc mymode 80
>> |       /set truncation mymode 45 expression
>> |       /set truncation mymode 0 vardecl-modified,replaced
>> |
>> |  Note that subsequent selectors for a field may overwrite some or 
>> all of previous used selectors -- last one wins
>>
>>
>>
>> On 09/22/16 10:42, Jonathan Gibbons wrote:
>>> In the long array case, I'd suggest to hide the middle, not the end 
>>> of the array.  Show the first "few" entries and the last "few" 
>>> entries in the array, for some value of "few".
>>>
>>> -- Jon
>>>
>>>
>>> On 9/22/16 10:37 AM, John Rose wrote:
>>>> On Sep 21, 2016, at 6:16 PM, Robert Field <robert.field at oracle.com> 
>>>> wrote:
>>>>> Comments???
>>>> Another +1 from me.  Some comments from my inner Common Lisper:
>>>>
>>>> There should be a close brace after the "…" of an overlong array.
>>>> This will allow syntax sensitive editors (emacs!) to block the 
>>>> thing correctly.
>>>>
>>>> The cutoff length of the overlong array should be a configurable 
>>>> number.
>>>>
>>>> You might consider a configurable cutoff for printed nesting level.
>>>>
>>>> These ideas from from this section of the CL manual:
>>>>
>>>> http://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node193.html#LEVELLENGTHTABLE 
>>>>
>>>>
>>>> There is also an option called *print-array* which gates whether 
>>>> arrays should be expanded at all.
>>>> This is relevant to Java, which also distinguishes Arrays.toString 
>>>> from Object.toString.
>>>>
>>>> — John
>>>
>>
>