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[REBOL] Re: relative expressions

From: g:santilli:tiscalinet:it at: 1-Apr-2003 14:57

Hi Gregg, On Tuesday, April 1, 2003, 6:00:25 AM, you wrote: BH>> I also wonder how multiple dialects can be usefully mixed together. I mean, BH>> lets say we have solved two problems plotting (qplot) and pdf making BH>> (pdfmaker) - shouldn't we aim to be able to mix them so that we could graph BH>> the number of words per section of a pdf file, or more usefully put a graph BH>> into a pdf? GI> Good example. I think a good plotting dialect would become a standard; GI> then people take that dialect and change the actions behind the rules GI> to do what they want in a new context. That brings up an important GI> design point. How to implement dialects so that kind of thing is as GI> easy as possible. This is something I've been thinking about too; actually, my custom-types ides came out from this thinking. If you think about REBOL's function interpreter, you see it is based on values. An expression is just a sequence of values, and depending on the type and the content of these values you get a result when it is evaluated. When we implement dialects using block parsing, we are using the same REBOL values to describe something, and the parser to interpret this and make actions or translate to something else. Now imagine if we had types of values that were designed specifically for our problem domain. In such a case, you would not even need PARSE rules, but only something that makes the correct actions for these values. (Notice that in REBOL the "methods" for datatypes are called "actions". I wonder if this is a coincidence.) This would solve the reusability problem, because you just have to change the actions. However, you still don't have an easy way to "write down" the values; this is where PARSE comes. You design a dialect with the rules to parse it and translate it to a (sequence of) (custom) value(s). It is like VID, that just translates to a FACE, which is then used by View. I really think that having custom types helps a lot with this; just having objects is fine with things like View, because you only have one kind of object, i.e. the FACE. In domains that are more complicated (maybe just because we are not smart enough to make them simpler...) you can easily have the need for many kinds of objects. So you get three layers: Language (dialect) ------------------ Values ------------------ Actions The "values" layer is something that you don't have in languages other than REBOL (at least that I know of). It is the layers that allows dialecting, and that gives REBOL all of its simplicity and flexibility; I think we should use this approach too! What do you think? Regards, Gabriele. -- Gabriele Santilli <[g--santilli--tiscalinet--it]> -- REBOL Programmer Amigan -- AGI L'Aquila -- REB: