for sure in your resarch you read create-your-own-dualvars. It tells $! is already dualvar:

perl -le "for (0..42){local $!; $! = $_; print 0 + $!, qq( - $!)}"

0 -
1 - Operation not permitted
2 - No such file or directory
3 - No such process
4 - Interrupted function call
5 - Input/output error
6 - No such device or address
7 - Arg list too long
8 - Exec format error
9 - Bad file descriptor
10 - No child processes
11 - Resource temporarily unavailable
12 - Not enough space
13 - Permission denied
14 - Bad address
15 - Unknown error
16 - Resource device
17 - File exists
18 - Improper link
19 - No such device
20 - Not a directory
21 - Is a directory
22 - Invalid argument
23 - Too many open files in system
24 - Too many open files
25 - Inappropriate I/O control operation
26 - Unknown error
27 - File too large
28 - No space left on device
29 - Invalid seek
30 - Read-only file system
31 - Too many links
32 - Broken pipe
33 - Domain error
34 - Result too large
35 - Unknown error
36 - Resource deadlock avoided
37 - Unknown error
38 - Filename too long
39 - No locks available
40 - Function not implemented
41 - Directory not empty
42 - Illegal byte sequence
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> but I did not find any way of driving an existing variable into schizophrenic behaviour.

All scalars are already schizophrenic (but using strict they claim for a psychologic support, not sure if for the compiler or for the programmer ;)

perl -wle "use strict; for my $x(@ARGV){ print qq(I was: $x); print qq
+(adding 1 I'm: ),$x + 1; print $x > 0 ? qq(I'm more than zero! ) : qq
+(I'm less than or zero! ); print $\ }" 0z 42A

I was: 0z
Argument "0z" isn't numeric in addition (+) at -e line 1.
adding 1 I'm: 1
I'm less than zero!


I was: 42A
Argument "42A" isn't numeric in addition (+) at -e line 1.
adding 1 I'm: 43
I'm more than zero!
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perl -wle "$x = q(a); print ++$x" prints b

L*

PS

This is even more weird.. I want to see if the numeric part of a filehandle was the same of what fileno returned.. it would be fun.. but no fileno

perl -lwe "open my $fh, '>', 'test'; print 0 + $fh; print + $fh"

16950176
GLOB(0x102a3a0)

# ..and no: 16950176 is not the sum of numerical values of characters
perl -wle "$str = q!GLOB(0x102a3a0)!; for (split '',$str){ print qq($_
+ = ),ord($_);$res += ord($_);} print $res"

G = 71
L = 76
O = 79
B = 66
( = 40
0 = 48
x = 120
1 = 49
0 = 48
2 = 50
a = 97
3 = 51
a = 97
0 = 48
) = 41
981
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PPS perl -wle "$x = q(a); print ++$x" prints b but not all chars are numeric, sorry I'm not JAPH, but J1PH1 :)

perl -we "print ++$_ for 'I@OG+' =~ /./g"

Argument "@" isn't numeric in preincrement (++) at -e line 1.
Argument "+" treated as 0 in increment (++) at -e line 1.
J1PH1
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