>724640 Vage Kategorien

Vague categories

Sometimes, a category is not described by a production but only by its name, for example when it would be difficult to describe the category by a production.

A vague category

.----------------.
| Any character  |
| except + and - |
'----------------'

In this course, we occasionally use the category »a character« with the meaning “one (arbitrary) character”.

Another vague category

.-------------.
| a character |
'-------------'

Each time a non-terminal is passed, a different text  can be chosen.

A production

double character
       .-------------.    .-------------.
|-|--->| a character |--->| a character |--->|-|
       '-------------'    '-------------'

A text of the category double character

/g

Ideally, vague categories should not be used at all to provide as clear a description as possible. In practice, however, they are used to avoid productions that would otherwise be too complicated or too large.

Practice Questions

?   Practice question

Production

        .-.     .-------------.    
|-|--->( + )--->| a character |--->|-|
        '-'     '-------------'

State exactly one  possible result of the above production rule.

?   Practice question

Production

       .-------------.     .-.     .-------------.    
|-|--->| a character |--->( + )--->| a character |--->|-|
       '-------------'     '-'     '-------------'

State exactly one  possible result of the above production rule.