Mailing List Archive: Re: a little help for a newbie?

[REBOL] Re: a little help for a newbie?

From: antonr:iinet:au at: 18-Feb-2003 12:56


Dave,

You have (understandably) misunderstood
how FOREACH is used. The first argument
to foreach is a word or a block of words
that *you* name, that will be set to
successive values in the second argument.
ie. It just so happens that Gabriele chose
good words [name style] to refer to each
pair of elements in system/view/vid/vid-styles.
He could have used [cow dog] as long as the
action block was [print cow].
Check out this console session:

	>> foreach [a b c] [1 2 3 4 5 6 7] [print [a b c]]
	1 2 3
	4 5 6
	7 none none

You can see that, because I specified [a b c] (three words),
that three numbers at a time are taken from the block.

Now, if you examine system/view/vid/vid-styles:

	>> probe system/view/vid/vid-styles

It gives you a really long block, that looks like this:

[face
    make object! [
        type: 'face
        offset: 0x0
        size: none
    ....
    ] IMAGE
    make object! [
        type: 'face
        offset: 0x0
        size: none
        span: none
        pane: none
    ] ....
    ....
    ....
]

(By the way, PROBE is really useful.)

What is it, though?

	>> type? system/view/vid/vid-styles
	== block!

What's inside it?

	>> type? system/view/vid/vid-styles/1
	== word!
	>> type? system/view/vid/vid-styles/2
	== object!

So the first thing inside is a word, and the second
thing is an object. If you continue, you see that the
third thing is again a word, and the fourth thing is
an object. So we have repeating pairs of elements.
We could have rewritten Gabriele's line:

	foreach [word object] system/view/vid/vid-styles [print word]

Here, 'object is being used only so that we skip
over the objects. Nothing is being done with it
in the action block [print word].
This reminds me of the relatively new function
EXTRACT:

	>> extract system/view/vid/vid-styles 2
	== [face IMAGE BACKDROP BACKTILE BOX SENSOR KEY VTEXT ...

How to see the facets of a face?
A face is really just an object with some standard
face elements
 in it. Do this to have a look at
the standard face:

	>> probe face

Now to get the list of facets:

	>> print mold first face

So our example:

	>> print mold first system/view/vid/vid-styles/button

Anton.