Take a look at Smart::Comments

c:\>perl -MSmart::Comments -lw
### assert: 42 == 42
### assert: 42 == 43
^Z

### 42 == 43 was not true at - line 2.


c:\>perl -MSmart::Comments -lw
### assert: 42 == 42
my $var = 43;
### assert: $var == 42
^Z

### $var == 42 was not true at - line 3.
###     $var was: 43
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