rgchris

Iterators, Part I

In this article, I will introduce iterators and discuss how they offer an intuitive interface for addressing a diverse set of programming problems. Specifically, I'll explore the potential application of iterators in Rebol, highlighting how they complement Rebol's elegant and expressive approach to problem-solving.

What are Iterators?

Iterators are mechanisms used to traverse complex data structures without exposing their internal composition. They provide a standard interface for accessing the component parts of those structures sequentially, significantly simplifying the code built around them. Iterators typically share the following characteristics:

• Encapsulation: They encapsulate the domain logic of a given data structure, meaning you do not need to learn that structure to use it.
• Sequential Access: Each call presents the next logical component from that domain.

rgchris

Tree-Walking Iterator

This script features an iterated method of traversing a tree-structure (specifically, a tree created by the Rebol 2 mezzanine PARSE-XML). The iterator returns events—OPEN, CLOSE, EMPTY, and TEXT—upon request until the tree has been fully traversed.

Concept Note

Using an iterated approach to tree traversal allows for fine control of the process that can be dropped and picked up fairly intuitively, effectively reducing the traversal process to a linear stream of events useful for serialization or extraction. This stands in contrast to the callback approach that fully traverses a tree firing callback functions until the tree has been fully traversed.

rgchris

#!/usr/local/bin/rebview -iv

Rebol [
    Title: "Intercepting Key events"
    Author: "Christopher Ross-Gill"
    Date: 23-Feb-2017

    Notes: [
        https://rebolforum.com/index.cgi?f=printtopic&topicnumber=579&archiveflag=archive
    ]

rgchris

Rebol [
    Title: "DSL Example"
    Author: "Christopher Ross-Gill"
    Date: 29-Jan-2023
    Home: https://gist.github.com/rgchris/2a227b6fa3fc9d2ae7fe729ccb09f016
]

reduce-only: func [
    "Evaluates a block of expressions excepting SET-WORD! values"

rgchris

// The journey to creating a new object type begins with ... a function
// * It doesn't have to be a named function (that is `function name()`
// as opposed to `name = function ()`) but there are advantages to this
// that are beyond the scope of this comment.
// * As a value, `myNumType` here serves double-duty--as a function in
// the sense of a passable first-class value, as, say, in Rebol
// * --and as a constructor for objects that use `myNumType` as a
// prototype
// * The value of `this` depends on the context in which the function
// `myNumType` is called. If you call it by itself, `this` refers to the

rgchris

Rebol [
    Title: "PDF Experiment"
    Author: "Christopher Ross-Gill"
    Date: 18-Jan-2022
    Home: https://gist.github.com/rgchris
    File: %pdf.r
    Version: 0.1.0
    Rights: http://opensource.org/licenses/Apache-2.0
    Purpose: {
        Build a PDF object model for atomic construction of PDF documents

rgchris

Rebol [
    Title: "Unzip for Rebol 2"
    Date: 3-Jan-2022
    Author: "Christopher Ross-Gill"
]

do %tiny-inflate.r
; obtain from
; https://gist.github.com/rgchris/d3fb5f6a6ea6d27ea3817c0e697ac25d

rgchris

#!/usr/local/bin/ren-r3c

Rebol [
    Title: "Package a Minimal OpenText Document"
    Date: 30-Dec-2021
    Author: "Christopher Ross-Gill"
    Rights: http://opensource.org/licenses/Apache-2.0
    Home: https://gist.github.com/rgchris/e325347625b1688a1a1fe686610c68ba
]

rgchris

Rebol [
    Title: "Tiny Inflate"
    Date: 10-Dec-2021
    Author: "Christopher Ross-Gill"
    Version: 1.0.3
    Type: 'module
    Name: 'rgchris.inflate
    Exports: [inflate]
    History: [
        10-Dec-2021 1.0.3 https://github.com/foliojs/tiny-inflate

rgchris

const Bd = function (name, attrs, ...kids) {
    const spaces = {
        xhtml: 'http://www.w3.org/1999/xhtml',
        svg: 'http://www.w3.org/2000/svg'
    }

    const fullname = name.split(':')

    name = fullname.pop()