All symbols used for representing a grammar may be the terminals of a metagrammar whose role is to generate a set of (related) grammars. For instance, the following metagrammar

RND [A grammar is a set of rules]

<1> S --> 'RND'; Ri

<10> S --> S ; R

----------------------

RND [Define context-free rules in Chomsky normal form]

Ri --> 'S' '-->' Arg2

R --> Arg1 '-->' Arg2

Arg1 --> Variable

<1> Arg2 --> Constant

<5> Arg2 --> Variable Variable

------------------------

RND

Variable --> X

Variable --> Y

Variable --> Z

Constant --> a

Constant --> b

Constant --> c

Constant --> d

generates any λ-free context-free grammar with variables {X,Y,Z} and terminal symbols {a,b,c,d}. 'S', 'RND' and '-->' are terminal symbols of the metagrammar itself, hence the single quotes. Semicolons generated by this grammar are automatically converted to line feeds.

Most grammars generated by "-gr.gramgene1" produce empty languages. There are better ways of producing grammars. A grammar called "-gr.gramgene2" on the BP2 disk may be used to generate (non-empty-language) pattern grammars such as for instance:

-ho.abc

RND

S --> Y Z

Y --> X X

Z --> X X

Y --> b

Z --> d

Y --> c

Z --> (=(= Z )(: Z ))(:(= Z )(: Z )) Y

Y --> d

Z --> X X

X --> b

X --> X Z

X --> a

X --> (= X )(: X ) Y