PAST representation of 'if'

• Create a PAST::Op node
• Set 'pasttype' attribute to 'if'
• Set first child as AST of condition
• Set second child as AST to evaluate if condition true

We can write this using Perl 6 syntax as:

method if_stmt($/) {
    my $past := PAST::Op.new(
                  $( $<expression> ),    # condition
                  $( $<statement> ),     # eval if true
                  :pasttype('if')
                );
    make $past;
}