def (1).g; end
     ^ cannot define singleton method for literals
def ((a; 1)).foo; end
         ^ cannot define singleton method for literals
def ((return; 1)).bar; end
              ^ cannot define singleton method for literals
def (((1))).foo; end
       ^ cannot define singleton method for literals
def (__FILE__).foo; end
     ^~~~~~~~ cannot define singleton method for literals
def (__ENCODING__).foo; end
     ^~~~~~~~~~~~ cannot define singleton method for literals
def (__LINE__).foo; end
     ^~~~~~~~ cannot define singleton method for literals
def ("foo").foo; end
     ^~~~~ cannot define singleton method for literals
def (3.14).foo; end
     ^~~~ cannot define singleton method for literals
def (3.14i).foo; end
     ^~~~~ cannot define singleton method for literals
def (:foo).foo; end
     ^~~~ cannot define singleton method for literals
def (:'foo').foo; end
     ^~~~~~ cannot define singleton method for literals
def (:'f{o}').foo; end
     ^~~~~~~ cannot define singleton method for literals
def ('foo').foo; end
     ^~~~~ cannot define singleton method for literals
def ("foo").foo; end
     ^~~~~ cannot define singleton method for literals
def ("#{fo}o").foo; end
     ^~~~~~~~ cannot define singleton method for literals
def (/foo/).foo; end
     ^~~~~ cannot define singleton method for literals
def (/f#{oo}/).foo; end
     ^~~~~~~~ cannot define singleton method for literals
def ([1]).foo; end
     ^~~ cannot define singleton method for literals