When comparing Rebol vs Assembly, the Slant community recommends Assembly for most people. In the question“What is the best programming language to learn first?” Assembly is ranked 49th while Rebol is ranked 51st. The most important reason people chose Assembly is:
One of the best ways to learn how a computer actually works is to work your way up from lower level abstractions. Assembly, being only a level above machine code, is low enough level to make it clear how the computer is actually performing a computation, including code flow and loops, but high enough level to not be excessively tedious for the type of small projects that a student would do at the beginning of their first programming class. Use of an assembler with macros can stretch this even a bit further.
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Pros
Pro Very simple syntax
Rebol's name came from "Relative Expression Based Object Language". Rebol is a functional language and everything is an expression that returns a value. Things that have to be baked into the grammar in other languages are simple function calls with block arguments in Rebol.
Pro Homoiconic
Code is data, and data can be code. Rebol is based on a simple block data structure, used both for data and for the code itself. Blocks can be manipulated programmatically, and then evaluated as code. This makes metaprogramming easy in Rebol.
Pro Human friendly
Almost natural language, for example: write %out.html read http://google.com
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Pro Graphical user interface
Beginners are usually stuck making command-line applications in other languages, because GUIs are too hard. Rebol GUIs are easy enough to start with.
Pro Domain specific languages
Rebol's simple homoiconic syntax makes it easy to create "Rebol dialects"--domain-specific languages optimized for a particular purpose. The Rebol distribution includes many of these, and users are free to create more. These DSLs make tasks that would be complicated to express in other languages easy.
Pro Low Level - it's how the computer works
One of the best ways to learn how a computer actually works is to work your way up from lower level abstractions. Assembly, being only a level above machine code, is low enough level to make it clear how the computer is actually performing a computation, including code flow and loops, but high enough level to not be excessively tedious for the type of small projects that a student would do at the beginning of their first programming class. Use of an assembler with macros can stretch this even a bit further.
Pro Naturally creates fast and small programs
Because of its natural syntax and low-level nature, assembly language programs are typically really small and fast.
Unlike other programming languages, in assembly language it is really hard to create a slow and over-bloated program.
Pro You must look into it if you really want to understand what computers do
There is no other way to understand a processor, so dig in.
Pro Useful for embedded systems
A curriculum that involves an embedded component, such as an Arduino or a Raspberry Pi, can encourage students by allowing them to immediately connect their work with 'real systems'. Assembly is the ideal language for getting started with and understanding these devices, and since Assembly can be called from C, the code will still be useful if students move on to C later in the program.
Pro Uniform syntax
Assembly language syntax is relatively uniform, and so there's less room for a student to get confused by obscure characters, or miss some meaning implied by structure, such as with scoping rules, or call-by-name/value/reference semantics. While there may be a lot of mnemonics to look up, most work involves only a very small subset of them.
Cons
Con Not (yet?) Free Software
Rebol 2's core is free (gratis) for commercial use, but the license prohibits modification, a violation of the DFSG. Rebol 3 is Free Software (Apache 2.0), but isn't production ready.
Con Very niche language
Small community.
Con No separators
A function call expression has no parentheses, and there are no separators between sequenced expressions, not even newlines. This means that you have to know the arity of every function in an expression to know how to parse it. It also means you can run into subtle, hard-to-find bugs if you don't provide enough arguments, since the result of the next expression will be passed instead.
Con Difficult learning curve
Starting off as a beginner with assembly language could prove very daunting. I suggest learning a high level language first (e.g. C) to get a good grasp of programming - especially dealing with bits, bytes, numbers, accessing memory with pointers (which is why I suggest C).
Then once that person is comfortable writing C (or whatever high level language) programs, they would find moving to assembler a little less of a "What the hell?!!!" experience.
Con Rarely a requirement or used in professional employment
(except for experts, which will outperform you in assembly language and execution speed on any day of the week, simply because they have full control of the processor.)
Con Not very portable
The instruction set may change depending on what CPU architecture is being used. Also, there will be some differences in implementations due to different assemblers being used, such as with changes in OS.
Con Language for those sadists that like pain
Not recommended as a first language. However, in small doses to show how higher level code is executed, can be of some value. Is also a language that will take a longer time to learn or finish projects with, so usually not for those who are in a hurry to get anything in particular done.