Changing GHC Error Message Wrapping

[Simon Peyton Jones]

-dppr-cols=N changes the width of the output page; you could try a large number there.  There isn't a setting meaning "infinity", sadly.

Simon

From: Andrew Gibiansky [mailto:andrew.gibiansky at gmail.com]
Sent: 07 January 2014 03:04
To: Simon Peyton Jones
Cc: Erik de Castro Lopo; ghc-devs at haskell.org
Subject: Re: Changing GHC Error Message Wrapping

Thanks Simon.

In general I think multiline tuples should have many elements per line, but honestly the tuple case was a very specific example. If possible, I'd like to change the *overall* wrapping for *all* error messages - how does `sep` know when to break lines? there's clearly a numeric value for the number of columns somewhere, but where is it, and is it user-adjustable?

For now I am just hacking around this by special-casing some error messages and "un-doing" the line wrapping by parsing the messages and joining lines back together.

Thanks,
Andrew

On Mon, Jan 6, 2014 at 7:44 AM, Simon Peyton-Jones <simonpj at microsoft.com<mailto:simonpj at microsoft.com>> wrote:
I think it's line 705 in types/TypeRep.lhs

pprTcApp p pp tc tys
  | isTupleTyCon tc && tyConArity tc == length tys
  = pprPromotionQuote tc <>
    tupleParens (tupleTyConSort tc) (sep (punctuate comma (map (pp TopPrec) tys)))

If you change 'sep' to 'fsep', you'll get behaviour more akin to paragraph-filling (hence the "f").   Give it a try.  You'll get validation failure from the testsuite, but you can see whether you think the result is better or worse.  In general, should multi-line tuples be printed with many elements per line, or just one?

Simon

From: ghc-devs [mailto:ghc-devs-bounces at haskell.org<mailto:ghc-devs-bounces at haskell.org>] On Behalf Of Andrew Gibiansky
Sent: 04 January 2014 17:30
To: Erik de Castro Lopo
Cc: ghc-devs at haskell.org<mailto:ghc-devs at haskell.org>
Subject: Re: Changing GHC Error Message Wrapping

Apologize for the broken image formatting.

With the code I posted above, I get the following output:

Couldn't match expected type `(GHC.Types.Int<http://GHC.Types.Int>,
                               GHC.Types.Int<http://GHC.Types.Int>,
                               GHC.Types.Int<http://GHC.Types.Int>,
                               t0,
                               t10,
                               t20,
                               t30,
                               t40,
                               t50,
                               t60,
                               t70,
                               t80,
                               t90)'
            with actual type `(t1, t2, t3)'

I would like the types to be on the same line, or at least wrapped to a larger number of columns.

Does  anyone know how to do this, or where in the GHC source this wrapping is done?

Thanks!
Andrew

On Sat, Jan 4, 2014 at 2:55 AM, Erik de Castro Lopo <mle+hs at mega-nerd.com<mailto:mle+hs at mega-nerd.com>> wrote:
Carter Schonwald wrote:

> hey andrew, your image link isn't working (i'm using gmail)
I think the list software filters out image attachments.

Erik
--
----------------------------------------------------------------------
Erik de Castro Lopo
http://www.mega-nerd.com/
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