[doublec]

You wouldn't write a conditional like that, you'd do:

    10 < [ "less than 10" ] [ "greater than 10" ] if

This is pretty easy to read. If the boolean condition is true, run the first quotation, if it is false, run the second.

The unusual names lke 'dip', 'bi', etc are just common names that once learned make code easier to read. 'dip' is from Joy IIRC.

I do agree that combinator heaviness can make things difficult for a beginner. Especially if code uses a combinator that isn't common it requires time to look up and see what it does. You really need to immerse in Factor development for a while to get familiar with them.

Stack effect declarations exist to make refactoring safer. Prior to having them enforced by the compiler it was common to change a words stack effect only to find it broke random code using it elsewhere. Making the check enforced provided a safety check that you hadn't forgotten to change word usage elsewhere.

[zvrba]

Oh, I've mixed up order of arguments to if.

The refactoring problem could have been solved in a more practical way (though more difficult implementation-wise) by implicit versioning of symbol definitions. Plus, I find that stack effect declarations read like line noise (see for example the declaration for if; IIRC from browsing the docs it's one of the moderately bad ones.)