Short answer , the author is implementing a state machine.

• &{...} is dereferencing a code-ref
• The subs are the actions per state.
• The goto &NAME syntax guaranties that the call stack isn't needlessly filled up with every state change. (See caller )
• The current state is kept as a code-ref in an attribute of the object ( blessed hash) passed as first argument.

The "weird" code ...

• goto &{$_[0]->{state} = \&stateReadLit};

... could be translated to a more explicit version:

my ($self,...) = @_;
...
my $c_next = $self->{state} = \&stateReadLit; # keep track
goto &{$c_next};
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or even

my ($self,...) = @_;
...
$self->{state} = \&stateReadLit;
goto &stateReadLit;
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update

Personally I have some doubt about this design decision, it doesn't seem like the code ref in $obj->{state} is ever used for anything more than a Boolean check.

If I was storing a state I'd use a readable name not a ref.