I'm sorry, I can't quite tell what your question is.

As for the syntax for grep, you can write a simple one two ways.

The first is with a block and without a comma.

grep { /x/ } @source;
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The second is with an expression and with a comma.

grep( /x/, @source );
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The second one can be written without the parentheses, but not without the comma.

grep /x/, @source;
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If you need to be more complicated than a simple expression, you need a block because you can't use a semicolon in a simple expression.

grep { my $x = $_;
       $x =~ s/\D//g;
       my $y = f( $x );
       ( $y > $x ) } @source;
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Sometimes you can cook a bit with operators.

grep s/\D//g && f( $_ ) > $_, @source;
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...but not always. The difference between the last two examples is that the second one modifies @source, while the second one doesn't.

Again, I can't tell what your question is, so I don't know if it helps. Hopefully there's something useful.