Hi, I am not sure about the rationale but if you need a program/library which re-renders Show-able values with more spaces, so that they are more human readable, I wrote one (http://hackage.haskell.org/package/pretty-show). I find it very useful for debugging. -Iavor On Sun, Feb 28, 2010 at 7:03 PM, Evan Laforge wrote:

This must be explained somewhere, but I can't find it.  I've always been curious why ghc's Show avoids all unnecessary spaces.  It's contrary to how most people format source so it can't be pasted into source, and can be hard to read.  Other languages tend to put in spaces.  I don't see anything in http://www.haskell.org/onlinereport/basic.html specifying the whitespace usage of Show.  I notice that the examples don't use spaces, but those are just examples, right?

What's the rationale? _______________________________________________ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime

Iavor Diatchki writes:

Hi, I am not sure about the rationale but if you need a program/library which re-renders Show-able values with more spaces, so that they are more human readable, I wrote one (http://hackage.haskell.org/package/pretty-show). I find it very useful for debugging.

This comes up sufficiently often that perhaps the Show class should have readableShow that defaults to the same as show. -- Jón Fairbairn Jon.Fairbairn@cl.cam.ac.uk

Evan Laforge writes:

On Mon, Mar 1, 2010 at 1:29 AM, Jon Fairbairn wrote:

...

Iavor Diatchki writes:

...

Hi, I am not sure about the rationale but if you need a program/library which re-renders Show-able values with more spaces, so that they are more human readable,  I wrote one (http://hackage.haskell.org/package/pretty-show).  I find it very useful for debugging.

This comes up sufficiently often that perhaps the Show class should have readableShow that defaults to the same as show.

The thing I was curious about was why Show doesn't default to a more pretty output in the first place.

Probably because that's not what it was originally intended for.

I actually have a separate Pretty class

So do quite a few people!

which, unlike Show, is under no obligation to produce parseable or even unambiguous output. This is similar to Python's concept of separate str() and repr() functions.

It makes little difference to me whether we have different classes for Pretty and Show or just a pshow in Show

And then a separate 'pshow :: Show a => a -> String' produces 'show' output but with newlines and all lined up. The missing bit is a Pretty that produces a Text.PrettyPrint Doc, but this can all be done without recourse to modifying the Prelude.

I think my argument is that producing human-readable output is a sufficiently common requirement that it should be fairly available from somewhere everyone knows to look. Personally, I'd remove most of the prelude and put more of it in standard libraries that everyone is expected to know about early on in learning the language. -- Jón Fairbairn Jon.Fairbairn@cl.cam.ac.uk