Tip #140: tip using embedded perl interpreter

When writing scripts using the embedded interpreter available if vim has the +perl ore +perl/dyn on
gives you access to this powerfull and FAST scripting language (especially fast compared to vim
scripts)  there are some gotchas.

First:
never embed complex perl command in the body of a vim function this will be recompiled and evaled
each time for a tremendous loss of time.instead to it like this

perl << EOF
sub mySub
{
  #some usefull perl stuff
}
EOF

function! MyFunction
perl mySub "an argument", "another"
endfunction

to pass computed argument to your perl sub use the vim exec command
function! MyFunction
exec "perl mySub " . aLocalVar . ", " b:aBufferLocalVar
endfunction

It may be very hard to debug your perl sub since the output of the perl compiler is
somehow lost in the middle of nowhere and the debugger is not available.
When a compilation error occurs in your sub definition you'll get an error message
when you try to call it saying that the sub does not exists.
One thing which I have found very usefull is to write a fake VIM module with stub
methods which will allow you to use the command line perl interpretor to at least
compile your program.  You could make your stub smart enough to fake a vim
and use the debugger.  Here is a sample for such a fake module defining just
those method which I was using.

package VIM;
use diagnostics;
use strict;
sub VIM::Eval
{
$_ = shift;

print "Eval $_\n";

{
  return '^(?!!)([^\t]*)\t[^\t]*\t(.*);"\t([^\t]*)\tline:(\d*).*$' if (/g:TagsBase_pattern/);
  return $ARGV[0] if (/b:fileName/);
  return '$3' if (/g:TagsBase_typePar/);
  return '$1' if (/g:TagsBase_namePar/);
  return '$4' if (/g:TagsBase_linePar/);
  return 'Ta&gs;' if (/s:menu_name/);
  return $ARGV[1] if (/g:TagsBase_groupByType/);
die "unknown eval $_";
}  
}
sub VIM::Msg
{
my $msg = shift;
print "MSG $msg\n";
}
sub VIM::DoCommand
{
my $package;
my $filename;
my $line;
    ($package, $filename, $line) = caller;

my $command = shift;
print "at $filename $line\n";
print "DoCommand  $command\n";
}
1;


Then you can copy other your perl code in a separate file and add a use VIM; at the top
and your set to debug.

Good Vimming good perling.
Benoit
PS:
this tips are probably true for other scripting languages

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