But what does the syntactically correct statement
    $expression ? $var = "foo" : $var = "bar";
actually do?

>perl -wMstrict -le
"for my $expression (0, 1) {
   my $var = '';
   $expression ? $var = 'foo' : $var = 'bar';
   print qq{if \$expression is $expression, \$var is '$var'}
   }
"
if $expression is 0, $var is 'bar'
if $expression is 1, $var is 'bar'
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It seems the statement is just an expensive equivalent to the statement
    $var = 'bar';
The reason why is left as a exercise for simonz (after the recommended perusal of perlop :)