I'm not sure if I have seen this requested or discussed.

Is there a parsing reason why Perl 6 would allow nested statement modifiers or 
is it mainly a sanity-please-don't-hurt-my-eyes reason.

It is silly to do things such as:

say "Interesting" if $just_because if $because;

But it is sort of useful to be able to do things such as:

say "Hrm $_" for 1 .. 3 unless $why_not;

The grammar_rules.pg defines a statement as:

token statement {
    | <statement_control>
    | <block>
    | <control_block>
    | <class_block>
    | <use_statement>
    | <expression:  ;> <statement_modifier>?

It seems like it should be possible to change that to:

token statement {
    | <statement_control>
    | <block>
    | <control_block>
    | <class_block>
    | <use_statement>
    | <expression:  ;> <statement_modifier>*

pge2past.tg would need to be updated to loop on found statement modifiers 
rather than only do the first one found.  I'm afraid I'm not familiar enough
with PIR to write the looping portion but I can read the following section 
enought to know that it shouldn't be too hard to change.  The question is 
would a patch to add the functionality be accepted if I went to the trouble 
of figuring out how to do it?

Paul Seamons

Section of pge2past.tg that re-writes the expression to be enclosed by an if 

transform past (Perl6::Grammar::statement) :language('PIR') {
    $P0 = node['statement_control']
    if $P0 goto statement_control
    $P0 = node['block']
    if $P0 goto statement_block
    $P0 = node['use_statement']
    if $P0 goto statement_use

    .local pmc stmt
    $P0 = node['expression']
    stmt = tree.'get'('past', $P0, 'Perl6::Grammar::expression')
    $P0 = node['statement_modifier']
    unless $P0 goto expression_1
    # handle if/unless modifier
    .local pmc modifier, exprpast, thenpast, elsepast
    modifier = $P0[0]
    thenpast = stmt
    null elsepast
    $S0 = modifier['KEY']
    if $S0 != 'unless' goto stmt_modifier_1
    exchange thenpast, elsepast
    $P0 = modifier['expression']
    exprpast = tree.'get'('past', $P0, 'Perl6::Grammar::expression')
    stmt = new 'Perl6::PAST::Op'
    stmt.'init'(exprpast, thenpast, 
elsepast, 'name'=>'statement_control:if', 'node'=>modifier)


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