#1062: Bad output from Text.PrettyPrint.HughesPJ
----------------------------+-----------------------------------------------
Reporter: igloo | Owner:
Type: bug | Status: new
Priority: normal | Milestone: _|_
Component: libraries/base | Version: 6.6
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Testcase: pp1 | Architecture: Unknown
Os: Unknown |
----------------------------+-----------------------------------------------
Old description:
> This program:
>
> {{{
> import Text.PrettyPrint.HughesPJ
>
> ncat x y = nest 4 $ cat [ x, y ]
>
> d1 = foldl1 ncat $ take 50 $ repeat $ char 'a'
> d2 = parens $ sep [ d1, text "+" , d1 ]
>
> main = print d2
> }}}
>
> generates the output below. I haven't worked out what is expected, but
> this certainly doesn't look right to me (in particular, the space before
> the `a` on the third line of the output).
>
> {{{
> % runghc pp1.hs | tr ' ' _
> (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
> +___________________________________________________________________________________________________________________________________________________________________________________________________a
> _a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a
> a)
> }}}
>
> The bug report goes on to say:
>
> {{{
> This code used to print an infinite string, by calling 'spaces'
> with a negative argument. There's a patch in the library now,
> which makes 'spaces' do somehthing sensible when called with a negative
> argument, but it really should not happen at all.
>
> This output is not what is expected, becuase the
> test "works" now, by virtue of a hack in HughesPJ.spaces.
> I'm leaving this strange output here to remind us to look
> at the root cause of the problem. Sometime.
> }}}
New description:
This program:
{{{
import Text.PrettyPrint.HughesPJ
ncat x y = nest 4 $ cat [ x, y ]
d1 = foldl1 ncat $ take 50 $ repeat $ char 'a'
d2 = parens $ sep [ d1, text "+" , d1 ]
main = print d2
}}}
generates the output below. I haven't worked out what is expected, but
this certainly doesn't look right to me (in particular, the space before
the `a` on the third line of the output).
{{{
% runghc pp1.hs | tr ' ' _
(aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+___________________________________________________________________________________________________________________________________________________________________________________________________a
_a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a)
}}}
The pp1 test goes on to say:
{{{
This code used to print an infinite string, by calling 'spaces'
with a negative argument. There's a patch in the library now,
which makes 'spaces' do somehthing sensible when called with a negative
argument, but it really should not happen at all.
This output is not what is expected, becuase the
test "works" now, by virtue of a hack in HughesPJ.spaces.
I'm leaving this strange output here to remind us to look
at the root cause of the problem. Sometime.
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1062>
GHC <http://www.haskell.org/ghc/>
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