REBOL: Концепция БЛОК

Blocks are used to hold both code and data. They are a fundamental concept in REBOL and it is important to know how to create and manipulate blocks.

Words and values are grouped into blocks, enclosed in square brackets [].

Within a block, values and words can be organized in any order and can span any number of lines.

You can see that both code and data use blocks.

Why brackets, not braces? REBOL uses square brackets because they are un-shifted on the US keyboard. Basically, they are easier to type. (Of course, that's not true on non-US keyboards, where it's probably best to setup a keyboard macro for [ and ].) Also, they seemed easier to read than braces (because they render as a cleaner glyph.) Also, REBOL's design was influenced just a small amount by Logo, the language from MIT created to help teach programming in schools.

Accessing strings and blocks

The extension library provides functions for accessing and creating strings and blocks. These functions are access via macros that use the library pointer passed in RX_Init.

RL_MAKE_BLOCK - make a new block of given length

RL_MAKE_STRING - make a new string of given length and width

RL_MAP_WORDS - map a block of words to their canonical symbol identifiers

RL_FIND_WORD - find word in an array of symbol identifiers

RL_SERIES_INFO - get series info: length, size, etc.

RL_GET_CHAR - get a char from a string

RL_SET_CHAR - set a char in a string

RL_GET_VALUE - get a value from a block

RL_SET_VALUE - set a value in a block

RL_GET_STRING - get string as an arrayIt is likely that more functions will be added as needed.

Note: allocation GC concerns

Code is held in blocks

https://rebol.tiddlyspot.com/#Code%20is%20held%20in%20blocks

Blocks aren't always evaluated

Blocks are not always evaluated. In many cases blocks may be skipped, due to the result of an expression.

Blocks return results

... all use print to display their results. That was done to make them clear, but the print hides an important fact: when evaluated, every block returns a result ... The result of blocks is often used in code, and you will be seeing it in many examples ahead.

Block Types

block! - Blocks of values

paren! - Blocks of values enclosed in parentheses

path! - Paths of values

list! - Linked lists

hash! - Associative arrays

Composing Blocks

The compose function is handy for creating blocks from dynamic values. It can be used for creating both data and code.

The compose function takes a block as an argument and returns a block that has each value in the argument block. Values in parentheses are evaluated before the block is returned.

https://rebol.tiddlyspot.com/#Concepts%3A%20Blocks%3A%20Composing%20Blocks