Fletch pointed out in the CB that using -x7 with B::Deparse gives the following confirmation: 

perl -MO=Deparse,-x7 -e "if ($a) { &BLOCK }"
$a and do {
    &BLOCK
};
-e syntax OK

[download]
Where if (EXPR) {BLOCK} is equivalent to EXPR and do { BLOCK } which confirms haukex's interpretation. It's worth noting that if the two forms are equivalent, the latter is probably a lot less confusing when the output value is used.

In reply to Re^3: printing unitialized value of the 'do BLOCK' by Eily
in thread printing unitialized value of the 'do BLOCK' by rsFalse

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