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
- 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.
