wtd @ Sat May 10, 2008 11:20 am wrote: I've tried to grok this language before, but I have to say, the lack of syntax really throws me off, and it doesn't even have Lisp's nice parentheses to indicate precendence.
Ahh, but it does. REBOL is based on series! Series of values. String! being series of char! binary! being series of bytes, but in the main it comes down to block! Blocks are series of values, any loadable values, and are surrounded by brackets. | REBOL: | [this is a block of words]
{what follows is a block of number! data, but in this string I can put anything including what REBOL would see as unloadable info such as $100,23,23,23.12xwe}
[1 2 3 $10 3.1415927] |
I highlighted loadable as REBOL's lexical scanner won't load $10,23,1. That is invalid money! and the loader will throw a syntax error. Nothing stops "$10,12,1" as a string!, but it can't be in a block! as a REBOL value. Anyway slowly getting to the point. Along with block! is paren! A paren! is an immediate block, that is surrounded by parentheses.
| code: | >> 10 * 3 + 2
== 32
>> 10 * (3 + 2)
== 50
>> 3 + 2 * 10
== 50
>> 3 + (2 * 10)
== 23
|
conceptually paren! allows programmer control over precedence, but it does so by immediately evaluating the code before resuming the regular make, load, do sequence. Not by complicating the lexical scanner in any C sense of the LEX/YACC BISON meaning that we are all used to, but simply by invoking the evaluator.
A biggy in REBOL is that block! information is not evaluated until told to. In the above example, I could have used [1 2 3 $10 pi] but the pi is just a word in the block.
| code: | >> probe [1 2 3 $10 pi (10 + 2)]
[1 2 3 $10.00 pi (10 + 2)]
== [1 2 3 $10.00 pi (10 + 2)] |
Note how the $10 was converted, that was by the make/load, not the evaluator and is part of the REBOL loadable datatype rules. The literal word pi was not, nor was the paren! expression - it is still in a block, waiting for a programmer to decide if it is code or data.
| code: | >> probe reduce [1 2 3 $10 pi (10 + 2) [pi]]
[1 2 3 $10.00 3.14159265358979 12 [pi]]
== [1 2 3 $10.00 3.14159265358979 12 [pi]] |
I forced the block evaluation with reduce, and the first pi is a defined word in the REBOL system context, so it gets reduced to it's value. The pi in the inner block is still data waiting for someone to tell it what's what in terms of the code is data and data is code concept, even with the first level of reduction going on.
block! and brackets is also the way of coding in control flow. | REBOL: | if 3 > b [print "b is less-equal to 3"] |
Anyway, I could talk about REBOL for days and days and days; I love it. But I'll stop now.
Cheers |
Different eh? Takes an open mind and a little time.
