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

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 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 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 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

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

-- Jun Inoue

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

-- Jun Inoue