Schemes

From DocBase

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.

1 Related Scheme Docs
2 Origin of the Name "Scheme"
3 Built-in schemes
4 Scheme object structure
5 Adding a new scheme

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Related Scheme Docs

Schemes:Notes

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Origin of the Name "Scheme"

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.

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Built-in schemes

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:

Scheme Description

system System port (primary event dispatcher)

stdio Standard input and output

stderr Standard error

console REBOL interactive console

file Local file access

dir Local file directory access

event GUI event handling

DNS Domain name lookup

TCP Transfer control protocol

UDP User datagram protocol

HTTP Hypertext transfer protocol

shell External shell commands (call)

serial Serial port access

USB USB serial port access

mutex Mutual exclusion locks

Scheme	Description
system	System port (primary event dispatcher)
stdio	Standard input and output
stderr	Standard error
console	REBOL interactive console
file	Local file access
dir	Local file directory access
event	GUI event handling
DNS	Domain name lookup
TCP	Transfer control protocol
UDP	User datagram protocol
HTTP	Hypertext transfer protocol
shell	External shell commands (call)
serial	Serial port access
USB	USB serial port access
mutex	Mutual exclusion locks

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]]

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Scheme object structure

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
an 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.

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