Throw an error if there are unfinished expressions

[danielcompton]

I accidentally didn't complete my last row of expressions, but Iota didn't warn about this because it's using partition and they were dropped. What do you think about throwing an error on invalid forms without complete tests?

[malcolmsparks]

Makes sense - perhaps using partition-all would be better.

[danielcompton]

I think this also relates a little to the use-case in #4.