Thursday, April 26, 2007

Factor Magic, Part 2

In the first part of this article, we looked through some graphics at how you can manipulate the stack with words. We visually examined the positions of the "values" on the stack before and after "shuffle" words were applied.

Copyright (C) 2007 Elie Chaftari

As a reminder take another look at the start position and the other subsequent effects once the rot, -rot, and swap words have been applied.

Another way to express these effects is through "stack notation". With stack notation you describe what parameters a word expects and what that word will leave on the stack once it has been applied.

( n1 n2 n3 -- n )

Here, for example, parameters n1 n2 n3 (in that order) are expected to be on the stack prior to the word's execution. They will be "consumed", leaving a new value n on the stack. A double dash separates input parameters from output parameters.

Let's put this new knowledge to profit to write the above diagram's effects.

rot ( n1 n2 n3 -- n2 n3 n1 ) causes the 3rd stack item to be moved to the top while the 1st and 2nd stack item are pushed down.

( n1 n2 n3 -- n3 n1 n2 ) causes the top stack item to be moved to the 3rd position while the 2nd and 3rd items are pushed up. A -rot, following a rot, returns the stack to the start position.

( n1 n2 -- n2 n1 ) exchanges the stack positions of the top two stack items.

A good place to discover the remaining shuffle words is in the Factor documentation. Another getting-started spot is the Factor tutorial in the online documentation.

Your "book of magic spells" needs more words of course and this takes some practice.

According to Doug Coleman, one of Factor's top gurus, you need to learn the following words by heart: dup, keep, 2dup, 2keep, swap, pick, rot, -rot, roll, -roll, 2apply, 2array, first2, nth, set-nth, append. He also advises to learn the following words for iterating: each, each-with, map, map-with, 2each, 2map.

Twenty-two words to learn are not a high price for a lot of power. Another nifty trick they'll teach you on the IRC channel is to enter: '\ word see' or '\ word help' in the listener to get immediate insight or help about any word.

( scratchpad ) \ swap see
IN: kernel
PRIMITIVE: swap ( x y -- y x )

Here you "see" the vocabulary (kernel) of the word swap and its stack effect.

If this quick introduction got you interested in more Factor magic, drop by at the IRC channel ( #concatenative) where you can ask for help and advice. See you there!

Wednesday, April 4, 2007

And the winner is...

The raptor dinosaurs are the fiercest because of their weapons, their speed and their intelligence. They have been chosen as a symbol because they are pack hunters like the Factor team.

However, since many would have liked to keep the lonely F icon; I have combined the two symbols with a backlit velociraptor in front of a large F. Here's a preview before I turn it into an icon.

[Image removed because of possible copyright infringement]

I just learned that even redrawing a photograph as an illustration could end up in a copyright suit. I'll either have to go out find a raptor who would graciously accept to pose for me or ask the author's permission.

Update: I usually don't surrender easily. Since no raptor was willing to pose for me, I decided to create my own. Refreshing my old 3D modeler skills, I created a low-poly mesh of a dino and posed it. After a first subdivision, I refined the mesh and extracted the outline. Below you can see the screen captures I took at each step.

Copyright (C) 2007 Elie Chaftari

I did not use any reference for the 3D model on purpose to avoid copyright issues. Here is the current state of the icon on Windows (Vista ready) and Macintosh.

Copyright (C) 2007 Elie Chaftari

Copyright (C) 2007 Elie Chaftari

Tuesday, April 3, 2007

Musing on a Factor icon

Ruby has the gem. Python has the snake. What is Factor's symbol?

I came up with this stack-like "F" to prompt more ideas. Jot down those ideas and let me know your thoughts in the comments.

Copyright (C) 2007 Elie Chaftari