>724400 Nichtterminalsymbole

Railroad Diagrams Non-Terminals

Railroad diagram

plus sign
        .-.
|-|--->( + )--->|-|
        '-'
double plus
       .-----------.    .-----------.
|-|--->| plus sign |--->| plus sign |--->|-|
       '-----------'    '-----------'

A square box can contain the name of a category, which means that a text of the named category must be inserted  in place of the box. In other words, the named production can be used in place of the square box.

After inserting the production for »plus sign«

double plus
       .-------------------.    .-------------------.
       |        .-.        |    |        .-.        |
|-|--->||-|--->( + )--->|-||--->||-|--->( + )--->|-||--->|-|
       |        '-'        |    |        '-'        |
       '-------------------'    '-------------------'

After inserting the production for »plus sign« and simplification

double plus
        .-.      .-.
|-|--->( + )--->( + )--->|-|
        '-'      '-'

Such a square box is also called a non-terminal  (or non-terminal symbol ).

The category double plus  thus includes the text »++«.

A double plus

++

A terminal

 .-.
( + )
 '-'

A non-terminal

.-----------.
| plus sign |
'-----------'

Practice Questions

?   Practice question

Railroad diagram

a
        .-.
|-|--->( 1 )--->|-|
        '-'
first
       .---.     .-.
|-|--->| a |--->( . )--->|-|
       '---'     '-'

Which text belongs to the category first  described above?