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Security

A distinguishing characteristic of PDC's version of Prolog is its type system which provides an extra level of security in programming. The type declarations document the code and allow the compiler to helpfully point out common typing mistakes as well as more serious mistakes in logic at the early stages of development. And by serving as a type of contract between programmer and development system, type declarations help ensure the integrity of a program over the entire product lifecycle.

domains
   sentence = sentence(nounphrase,verbphrase)
   nounphrase = noun(article,noun); name(name)
   verbphrase = verb(verb); verbphrase(verb,nounphrase)
   article,noun,name,ver = symbol
predicates
   handle_sentence(sentence)
   handle_nounphrase(nounphrase)
   handle_verbphrase(verbphrase)

Declaration of domains (data types) and predicates (procedures) improves the readability of source code, decreases the number of programming errors, and allows the compiler to generate faster and more efficient machine code.

Error and Exception Handling

Run-time error and exception handling is critical to providing a bulletproof program that users feel they can rely on. Visual Prolog has predicates to trap run-time errors and exceptions as well as to maintain complete control over and detection of user-generated exceptions.