Up: Purity

Domains

A domain contains facts and rules about a particular type of knowledge. From Purity's point of view, a domain is a type of data, but custom domains can be created to contain any set of facts and rules. Several library calls in Purity have a domain as a parameter and this call will usually use the domain parameter to do comparisons.

The following domains come standard with the Purity library:

• pchar - A domain containing the following characters:
  • The character set [a-zA-Z0-9]
  • The digits [0-9]
  • The following symbols `;:",?/\<>,.!@#$%^&*()[]{}|-_+=`
  • Whitespace characters `<space>\n\r\t`
• pstring - Strings which are represented by a list of pchar characters. pstring is the equivalent of plist(pchar) when using comparisons, however there are a special set of APIs that start with pstr_ that only use the pstring domain.
• plist(D) - Lists which can be of type D where D is a domain.
• punary - Unary numbers (or natural numbers) using church encoding
  • zero = 0
  • c(zero) = 1
  • c(c(zero)) = 2
  • etc..