search

GetPoplog / Grammar

Managing the Pop-11 Grammar
Creative Commons Zero v1.0 Universal
2 stars 1 forks source link

Adding empty expressions #10

Closed edgardozoppi closed 2 years ago

edgardozoppi commented 2 years ago

Resolves #7 issue.

edgardozoppi commented 2 years ago

Now almost all existing uses of Expression have became NonEmptyExpression, except the usage for function arguments. This makes me consider doing the opposite thing of creating a new non-terminal PossibleEmptyExpression that is only used for function arguments and leave as Expression all the other usages that require a non-empty expression. I believe it feels more natural. What do you think?

sfkleach commented 2 years ago

Now almost all existing uses of Expression have became NonEmptyExpression, except the usage for function arguments. This makes me consider doing the opposite thing of creating a new non-terminal PossibleEmptyExpression that is only used for function arguments and leave as Expression all the other usages that require a non-empty expression. I believe it feels more natural. What do you think?

Although I agree with the sentiment, in actual fact Pop-11 allows empty-expressions in far too many places. (Later on in this project I intend to produce a modified version of the Poplog compiler that is a bit stricter about empty expressions. But for now we need to stick to what is implemented.)

This PR goes quite a bit further than my user story - and that's where it is not quite right. I have made explicit notes everywhere in the EBNF, which I find much easier to read.

And finally I do appreciate that this loose treatment of empty-expressions will seem like catastrophically bad syntax design & I am highly amused imagining your reaction at some of my examples - all of which are drawn from a live Pop-11 interpreter! In my personal opinion it is poor syntax design but in practice it rarely causes problems. Exactly why it causes so few problems I haven't ever really come to a good conclusion over. I suspect that it is as simple as omitting entire expressions is a rare blunder.