Make the grammar more consistent, and explain rewrite based on feedback.

[HansOlsson]

During the conference we got feedback that the grammar is ambiguous.

I understand that the problem is due to trying to make the grammar more logical - but:

• We should be consistent; so that equations and statements are treated in a similar way.
• We might as well explain it - people familiar with parsers should just be able to read the grammar.

[HansOlsson]

We could also add:
Similarly if output-expression-list is not merely an expression it is only allowed in statement as explicitly given and in equation-or-procedure matching "(" output-expression-list ")" = component-reference function-call-args