A scheme specifies a type of port. Schemes are defined for files, networking, sound, and many other functions. Users can define their own schemes or modify the existing schemes.

• Schemes Notes

The name scheme comes from the standard description of a URI (URL). In this URL:

http://www.rebol.net/index.html

HTTP is the scheme name, www.rebol.net is the host, and index.html is the file path. Rebol uses that same naming convention.

A variety of schemes are built-into Rebol 3 and can be used immediately on boot.

Here is a partial list of built-in schemes:

More (such as FTP, SMTP, POP) will be included as time and user-base contributions permit.

To obtain a list of the current schemes, you can write:

probe words-of system/schemes

or:

foreach val get system/schemes [print [val/name val/title]]

The scheme object is defined in system/standard as:

scheme: context [
    name:       ; word of http, ftp, sound, etc.
    title:      ; user-friendly title for the scheme
    spec:       ; custom spec for scheme (if needed)
    info:       ; prototype info object returned from query
    actor:      ; standard action handler for scheme port functions
    awake:      ; standard awake handler for this scheme's ports
        none
]

Where:

name

Is the type of scheme. This is the word used in the first part of the URL, such as TCP, HTTP, FTP, etc.. It must be a valid Rebol word (e.g. cannot begin with a number).

title

Is the title of the scheme for user identification and documentation purposes.

spec

An object used to specify additional features of the scheme.

info

A prototype object that is instantiated for a query on the scheme.

actor

The handler function that processes standard actions a port of this scheme type. For example, open, close, read, write, etc.

awake

A callback function that is invoked when new events arrive for a port of this scheme type.

The make-scheme function creates a new scheme from a block object specification.

(show example)

Draft Notes