[Haskell-cafe] How can I use ghci more wisely?

[Jun Inoue]

Thanks for the tip, David, I didn't know about that flag!  Looks
really handy for playing with EDSLs, which is usually better off
displayed through Doc, but the default Show instance is indispensable
when I find a bug in the conversion to the Doc.

Unfortunately, though, I'd be reluctant to make data-pprint the
universal default as it is now.  I forgot to mention this in my
previous post, but data-pprint doesn't let you customize the output
per-datatype.  It just works generically over Data.Data instances and
the format is fixed to be the same as default Show instances (except
for lists, which are special-cased internally).  So as annoying as the
explicit pprint is, I see it as a necessary evil.  Perhaps I can
generalize its interface and send a patch.  I have some ideas but
never got around to trying them.


On Wed, Jul 24, 2013 at 10:16 PM, David McBride <toad3k at gmail.com> wrote:
> You might like to know about this option for ghci -interactive-print
>
> I tested it with data-pprint though and it didn't work because it
> returns an IO Doc instead of IO () (I assume).  But if you wrote a
> function that used that, returned the right type, cabal installed it
> and put it in your .ghci, you would have your pprinting by default
> whenever you use ghci.
>
> On Wed, Jul 24, 2013 at 7:33 AM, Jun Inoue <jun.lambda at gmail.com> wrote:
>> The data-pprint package's pprint function might give you a quick fix.
>> For example:
>>
>> Prelude> :m Data.PPrint
>> Prelude Data.PPrint> pprint [1..]
>> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
>>  20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,
>>  37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53,
>>  54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70,
>>  71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87,
>>  88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103,
>>  104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116,
>>  117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129,
>>  130, 131, 132, 133, 134, 135, …, ……]
>> Prelude Data.PPrint> let long_computation = long_computation
>> Prelude Data.PPrint> pprint [1, long_computation, 3]
>> [1, ⊥₁, 3]
>>   ⊥₁: timeout at 0%
>>
>> It's a bit of a hassle to have to type "pprint" all the time though,
>> and it doesn't give you a way to show the data without printing to the
>> terminal in the IO monad.
>>
>> On Wed, Jul 24, 2013 at 4:30 AM, yi lu <zhiwudazhanjiangshi at gmail.com> wrote:
>>> I am wondering how can I ask ghci to show an infinite list wisely.
>>> When I type
>>>
>>> fst ([1..],[1..10])
>>>
>>> The result is what as you may guess
>>>
>>> 1,2,3,4,...(continues to show, cut now)
>>>
>>> How could I may ghci show
>>>
>>> [1..]
>>>
>>> this wise way not the long long long list itself?
>>>
>>> Yi
>>>
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>>> Haskell-Cafe at haskell.org
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>>
>>
>>
>> --
>> Jun Inoue
>>
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-- 
Jun Inoue