The allomorph lexicon is generated from the base form lexicon by applying the allo-rule on the base form entries. The allomorph generation rule file has the suffix .all and consists of one allo-rule, an optional output-filter, and any number of subrules and constant definitions.
For every lexical entry, the allo-rule is executed with the value of the
lexicon entry as parameter. The allo-rule can generate allomorphs using the
result statement.
After all allomorphs have been produced, the output-filter is executed once for
each surface in the (intermediate) allomorph lexicon. As parameter, the
output-filter gets the list of feature structures that share that surface. An
entry in the final allomorph lexicon is created everytime the result
statement is executed. The surface cannot be changed by the output-filter.