There's no default.

If you say there's such a thing as a list in scalar context, it's because you're talking about list literals or the list operator. If so, the only behaviour for a list in scalar context is to return its last element after evaluating it in scalar context. undef is returned for empty lists.

# List literal in list context
>perl -E"sub c { @a=qw(d e f g); @a } say('a', 'b', c())"
abdefg

# List literal in scalar context
>perl -E"sub c { @a=qw(d e f g); @a } say(scalar('a', 'b', 'c'))"
c

# List literal in scalar context
>perl -E"sub c { @a=qw(d e f g); @a } say(scalar('a', 'b', c()))"
4   # scalar(@a)
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