User-defined rules

You can define rewrite rules for the PHI language using YAML and the MetaPHI language that is a superset of PHI.

MetaPHI

See the MetaPHI Labelled BNF in Syntax.cf.

phi-paper rules

Currently, the eo-phi-normalizer supports rules defined in an unpublished paper by Yegor Bugayenko.

yegor.yaml

The rules are defined in yegor.yaml.

Each rule has the following structure:

• name - Rule name.
• description - Rule description.
• context - (optional) Rule context. A context may contain:
  • global_object - (optional) Global object MetaId.
  • current_object - (optional) Current object MetaId.
• pattern - Term pattern written in MetaPHI.
  • The pattern must be an object (formation, application, dispatch, etc.)
  • When this term pattern matches a subterm of a PHI term, MetaIds from the term pattern become associated with matching subexpressions of that subterm.
• result - Substitution result.
  • MetaIds in the subterm pattern get replaced by their associated subexpressions.
• when - A list of conditions for pattern matching.
  • nf - A list of MetaIds associated with subexpressions that should be in the normal form.
    • An expression is in the normal form when no rule can be applied to that expression.
  • present_attrs - A list of attributes that must be present in subexpression bindings.
    • attrs - A list of attributes. Can include MetaIds.
    • bindings - A list of bindings that must contain these attributes.
  • absent_attrs - A list of attributes that must not be present in subexpression bindings.
    • attrs - A list of attributes. Can include MetaIds.
    • bindings - A list of bindings that must not contain these attributes.
• tests - A list of unit tests for this rule.
  • name - Test name.
  • input - An initial PHI term.
  • output - The initial PHI term after this rule was applied.
  • matches - Whether the term pattern should match any subterm.