Predicate Variables Extension

This extension will allow people to define proof rules for the Rule Based Prover using meta-variables as predicate placeholders.

For example, one will then be able to write a proof rule involving P and Q directly by using such naming letters to refer to an existing predicate declaration.

The meta-variables will be identified with the symbol '$'. For one given predicate, one wanting to refer to this predicate as P, will write in his proof rules, the meta-variable '$P'. The symbol '?' could be originally chosen to define meta-variables but this revealed to be confusing due to the use of the symbol '?' in the CSP language. The choice of the symbol '$' seems to solve such type of issue.

Plan to implement this extension in the API

• A. extend the lexer
• B. extend the parser
• C. extend the AST
• D. modify visitors, rewriters, filters, etc. accorded to this extension
• E. implement new AST tests

Implementation details

For B, clients (plug-in contributers) will be allowed to select the mode they want to work with. Thus, will coexist 2 parsing modes one taking into account predicate variables and the other, the current one, which parses predicates or expressions without predicate variables.

- the current one available in the current API (FormulaFactory),

 public IParseResult parsePredicate(String formula, LanguageVersion version,Object origin)
 public IParseResult parseExpression(String formula, LanguageVersion version,Object origin)

- a specific one providing the support for predicate variables.

 public IParseResult parsePredicatePattern(String formula, LanguageVersion version,Object origin)
 public IParseResult parseExpressionPattern(String formula, LanguageVersion version,Object origin)

For C, the class 'PredicateVariable' will be added as a new predicate class. In the Formula class will be added PredicateVariable[] getPredicateVariables() and boolean hasPredicateVariables() methods.

Further verifications to carry out

A verification will follow implementation, in order to check that no side-effects were introduced by this extension. We will trace and verify that no external processing on predicates returns predicates containing predicate variables. For example, one must ensure that there isn't no call to the "typeCheck()" method in the platform's code that doesn't follow a call to parsePredicate(). The aim is to verify that no predicate variables remain at the time of the "typeCheck()" call.