1.64 class function

A function object is a code object that, when function<-execute’d, returns a PCE data object as the virtual machine instruction get(). Functions are evaluated iff:

• They appear as part of a code object that is executed
• They are passed to the type-checker (see type<-check) and the type does not allow for functions to be passed.

  Explicit evaluation is achieved using function<-execute and function<-forward. Quoting (e.i. delaying evaluation) is achieved using a quote_function object.

  PCE currently provides the following functions:

• Class ? (obtainer) An obtainer represents a get() operation. It evaluates to the return value of the get operation represented.
• Class binary_expression Super-class for the common arithmetic functions: +, -, *, /
• Class var A var represents a PCE variable. Among these are the predefined variables @arg1 ..., @receiver, @event, etc.
• Class when A when is a conditional function. It may be compared to Lisp's if or C's Cond ? Expr1 : Expr2.
• Class progn Sequence of statements closed with a function.
  NOTE: Many methods defined on class object reappear on this class. The message passing system will, when the receiver is a subclass of class function, not evaluate the function if the method is defined at the level of class function or lower in the class hierarchy.

  See also

  - type<-check
  - class code

1.64.1 Get methods

function <-_execute: -> unchecked

Objects of class function itself cannot be executed. Yields an error message and fails. Redefined by all subclasses of class function.

function <-forward: any ... -> unchecked

function <-_forward: any ... -> unchecked

Bind @arg1, ... from the arguments and function<-execute the function. Note that @arg1 is a function itself, thus

?- get(@arg1, forward, 4, X).		==> X = 4

function <-convert: quote=quote_function -> function

Converts an instance of class quote_function into the function quoted. See class quote_function for details.

function <-execute: -> unchecked

Explicitly evaluate the function. See class function itself for the default evaluation rules. Class quote_function avoids evaluation of function objects.

Calls function<-_execute to perform the real job.