OpenEuphoria

You're right - it is easier to just have the developer specify intent and let the parser enforce it. But I think we can still keep it within desequencing:

function foo(sequence this, integer update_value) 
    integer prior_value = this[1] 
    this[1] = update_value 
    return using desequencing with size 2 values {this, prior_value} -- we can come up with a better syntax than this 
end function 
 
object spare 
sequence this = {50} 
this = foo(this, 11) -- parser blows up here since we aren't using desequencing, but we stated that we intended the caller of this function must use it. 
{this} = foo(this, 11) -- parser blows up here since it can tell that there's a size mismatch 
{this, ?} = foo(this, 11) -- parser allows this 
{this, spare} = foo(this, 11) -- parser allows this