REBOL 3 Datatypes: Function!

Contents

Concept

The REBOL language contains a few different types of functions, including native!, action!, function!, and closure!. The main thing that makes them different is how they are evaluated.

The function! datatype is a higher level function that is interpreted. They are also called user-defined functions, and system functions defined this way are called mezzanine functions.

Format

Functions consist of a specification and a body block. The specification part provides the interface specification and any embedded documentation. The body is the code of the function.

The formal definition of function is:

make function! [[specs] [body]]

(However, functions are normally created using helper functions. See below.)

Changed from R2

Note that this format changed from REBOL V2. This change was necessary because make accepts only two arguments. Therefore, the second argument contains the specs block and the body block.

The function specs block holds:

arguments	the arguments passed to the function.
datatypes	optional datatype specifications for each argument.
refinements	optional variations in the behavior and arguments of a function.
doc strings	embedded documentation for the function and its arguments.

For every argument it is possible to define how the argument is passed to the function using one of the formats:

Notation	Meaning
word	The argument expression is evaluated before it is passed to the function.
'word	The argument expression is evaluated only if it starts with a get-word! or a paren!.
:word	The argument expression is not evaluated. The very next value is used.
word:	Reserved. Used to define variations.

Creation

Normally, you create a function! using a helper function. There are a few choices:

func	Is the most common function defining function.
funct	Is similar to func, but by default makes internal variables locals.
has	Is for creating functions that have no formal arguments, only local variables.
does	Is for creating functions that have no variables at all.

More about functions is found in code: defining functions.