That was my first idea too ...

... but I think something is fundamentally broken with the parsing of prototyped sub calls.

see how + fails ...

lanx@lanx-1005HA:/tmp$ perl -MO=Deparse -e 'sub foo (&) {}; foo {"foo"
+} + 3'
Too many arguments for main::foo at -e line 1, at EOF
-e had compilation errors.
sub foo (&) {
    
}
&foo(sub {
    'foo';
}
, 3);
[download]

... while . works

lanx@lanx-1005HA:/tmp$ perl -MO=Deparse -e 'sub foo (&) {}; foo {"foo"
+} . "3"'
sub foo (&) {
    
}
foo(sub {
    'foo';
}
) . '3';
-e syntax OK
[download]

Seems like the parser tries to guess if a second parameter follows even if no further parameters are allowed.

The + fails because it's also a unary operator, so the foo( BLOCK, +3 ) interpretation is preferred, but later rejected, without backtracking into another, binary interpretation.

I'm no expert of how the lexer works but implementing parsing on such heuristics is a fragile thing.

Hopefully this can be fixed in the future.

update

that's really a depressing bug, I had much hope in using more block prototypes.