Appear

The purpose of this transformation operator is to insert an nillable symbol (i.e., reducible to an empty sequence) at any place in any existing grammar production rule. It takes a production rule as an input. Inside that, one nillable subexpression should be marked.

Syntax

appear:
        marked-production

Example

Given the input:

foo:
        bar

After using this transformation:

appear(
 foo:
        bar <qux?>
);

The result will look like this:

foo:
        bar qux?

Relevant files

• shared/prolog/xbgf1.pro
• shared/rascal/src/transform/library/Sequential.rsc
• shared/xsd/xbgf.xsd

See also

• Appear is a part of XBGF

Contributors

• Ralf Lämmel (@rlaemmel)
• Vadim Zaytsev (@grammarware)