Empty Expressions

[sfkleach]

Allow expressions to be empty, as per line 189 of POPSYNTAX and introduce the non-terminal NonEmptyExpression. Use NonEmptyExpression to ensure the left-hand side of a FunctionApplication is non-empty. Simplify where appropriate.

Acceptance Criteria

EBNF:

• [ ] Expression may be empty
• [ ] FunctionApplication left hand side is a non-empty expression
• [ ] All uses of Expression? should be simplified as Expression

Identical criteria for Tabatkins grammar:

• [ ] Expression may be empty
• [ ] FunctionApplication left hand side is a non-empty expression
• [ ] All uses of Expression? should be simplified as Expression

[edgardozoppi]

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?