[wantarray]

I'm pretty sure that the "expression-lambdas" were inspired by Haskell, where you get a lambda simply by writing an operator with one or more missing operands.

In Perl 6, detecting that an operand is "missing" isn't possible due to the existence of prefix/infix/postfix operators with the same names, so it expects a "whatever" star in place of the missing operand... :)