Deparse isn't as reliable as I thought

I don't know how usefull this will be to anyone. It's rather obscure. Perldoc -f split says:

As a special case, specifying a PATTERN of space (’ ’) will split on white space just as "split" with no arguments does. Thus, "split(’ ’)" can be used to emulate awk’s default behavior, whereas "split(/ /)" will give you as many null initial fields as there are leading spaces. A "split" on "/\s+/" is like a "split(’ ’)" except that any leading whitespace produces a null first field. A "split" with no arguments really does a "split(’ ’, $_)" internally.

That reads like stereo instructions. I think I understand it but it appears that B::Deparse is having problems with it:

#!/usr/bin/perl -w

$string = '   abc   def   ';

@array1 = split " ", $string;

@array2 = split ?\s+?, $string;

print '2: ' . ( join '|', @array1 ) . "\n";

print '3: ' . ( join '|', @array2 ) . "\n";
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Run it through deparse and you get:

BEGIN { $^W = 1; }
$string = '   abc   def   ';
@array1 = split(?\s+?, $string, 0);
@array2 = split(?\s+?, $string, 0);
print '2: ' . join('|', @array1) . "\n";
print '3: ' . join('|', @array2) . "\n";
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Run this script and you get the following output:

2: abc|def
3: |abc|def
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This caused me to not trust Deparse quite so much. I'm going to be a little more careful about trusting what Deparse spits out.

Harley J Pig

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Re: Deparse isn't as reliable as I thought
by PodMaster (Abbot) on Mar 03, 2006 at 22:37 UTC

C:\>perl -MO=Concise -e"@f = split ' ', shift"
9  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 1 -e:1) v ->3
8     <@> split[t5] vK ->9
3        </> pushre(/"\\s+"/ => @f) s*/64 ->4
6        <1> shift sK/1 ->7
5           <1> rv2av[t4] sKRM/1 ->6
4              <#> gv[*ARGV] s ->5
7        <$> const[IV 0] s ->8
-e syntax OK

C:\>perl -MO=Concise -e"@f = split /\s+/, shift"
9  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 1 -e:1) v ->3
8     <@> split[t5] vK ->9
3        </> pushre(/"\\s+"/ => @f) s/64 ->4
6        <1> shift sK/1 ->7
5           <1> rv2av[t4] sKRM/1 ->6
4              <#> gv[*ARGV] s ->5
7        <$> const[IV 0] s ->8
-e syntax OK

C:\>perl -MO=Concise -e"@f = split ?\s+?, shift"
9  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 1 -e:1) v ->3
8     <@> split[t5] vK ->9
3        </> pushre(/"\\s+"/ => @f) s/64 ->4
6        <1> shift sK/1 ->7
5           <1> rv2av[t4] sKRM/1 ->6
4              <#> gv[*ARGV] s ->5
7        <$> const[IV 0] s ->8
-e syntax OK
[download]

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Re^2: Deparse isn't as reliable as I thought

by harleypig (Monk) on Mar 04, 2006 at 00:21 UTC

Thanks. I didn't know about Concise.

The only difference I can see in these two is the asterisk (*):

</> pushre(/"\\s+"/ => @f) s*/64 ->4 (split " ")
</> pushre(/"\\s+"/ => @f) s/64 ->4 (split ?\s+?)
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The most I've been able to find out is that the '*' means 'do something weird for this op' and a reference to op.h, which says 'On pushre, re is /\s+/ imp. by split " "'. We already know this.

So this is gonna have to be one of those cases where I'm just gonna have to accept it as a peculiarity of perl. This is not a big issue as I won't be running into this any time soon again.

Also, the magic only happens when assigning to an array, using in implied contexts or assigning to a scalar the " " is *not* converted to ?\s+?.

Harley J Pig

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Re^2: Deparse isn't as reliable as I thought

by ambrus (Abbot) on Mar 05, 2006 at 23:35 UTC

Well, Concise doesn't even distingush between

perl -MO=Concise -we 'warn "foo"=~/f./g'
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perl -MO=Concise -we 'warn "foo"=~/f./'
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Re^3: Deparse isn't as reliable as I thought

by BrowserUk (Patriarch) on Mar 05, 2006 at 23:52 UTC

See what happens when you put that into a list context:

C:\>perl -MO=Concise -e"'foofoo' =~ /f../"
5  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 1 -e:1) v ->3
4     </> match(/"f.."/) vKS/RTIME ->5
3        <$> const[PV "foofoo"] s ->4
-e syntax OK

C:\>perl -MO=Concise -e"'foofoo' =~ /f../g"
5  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 1 -e:1) v ->3
4     </> match(/"f.."/) vKS/RTIME ->5
3        <$> const[PV "foofoo"] s ->4
-e syntax OK

C:\>perl -MO=Concise -e"() = 'foofoo' =~ /f../g"
8  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 1 -e:1) v ->3
7     <2> aassign[t1] vKS/COMMON ->8
-        <1> ex-list lK ->6
3           <0> pushmark s ->4
5           </> match(/"f.."/) lKS/RTIME ->6
4              <$> const[PV "foofoo"] s ->5
-        <1> ex-list lK ->7
6           <0> pushmark s ->7
-           <0> stub lPRM* ->-
-e syntax OK
[download]

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In the absence of evidence, opinion is indistinguishable from prejudice.

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Re: Deparse isn't as reliable as I thought
by Jenda (Abbot) on Mar 04, 2006 at 01:32 UTC

Well, deparse doesn't seem to work on my notebook at the moment for the script so I can't check it out so it may be totally irrelevant, but ... are you sure you want to use ?\s+? instead /\s+/? Maybe it doesn't matter in split(), but ... from perldoc perlop:

?PATTERN?
This is just like the "/pattern/" search, except that it matches only once between calls to the reset() operator. This is a useful optimization when you want to see only the first occurrence of something in each file of a set of files, for instance. Only "??" patterns local to the current package are reset.

Jenda
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Re: Deparse isn't as reliable as I thought
by davido (Cardinal) on Mar 04, 2006 at 05:33 UTC

One of the marks of a good obfuscation is one that runs fine as coded, but fails to run in its B::Deparse'd version. B::Deparse isn't perfect. Only perl can 100% reliably parse Perl. And even then it's probably only 99.99999% reliable. ;)

Dave

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Re^2: Deparse isn't as reliable as I thought

by diotalevi (Canon) on Mar 04, 2006 at 06:03 UTC

Deparse doesn't parse perl either. It generates perl. Every time Deparse fails to produce source code that compiles back to the same thing, that's a bug. There are no obfuscations that should be undeparseable.

⠤⠤ ⠙⠊⠕⠞⠁⠇⠑⠧⠊

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Re^3: Deparse isn't as reliable as I thought

by truedfx (Monk) on Mar 04, 2006 at 09:17 UTC

BEGIN { close STDOUT; }

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Re^4: Deparse isn't as reliable as I thought

by diotalevi (Canon) on Mar 04, 2006 at 16:29 UTC

Re^5: Deparse isn't as reliable as I thought

by truedfx (Monk) on Mar 04, 2006 at 19:36 UTC

Re^3: Deparse isn't as reliable as I thought

by Steve_p (Priest) on Mar 04, 2006 at 13:41 UTC

Agreed. Several modules depend on the proper functioning of B::Deparse. If there is a difference, you should report the bug with perlbug. Please provide the test scripts so this can problem can be investigated.

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