[REBOL] Re: [data structures] (was Re: [append][series]Appending to a series of
From: lmecir:mbox:vol:cz at: 21-Nov-2003 9:43
Hi Joel and all,
Joel Neely napsal(a):
...snip...
>The design of every language with which I'm familiar reflects at least
>two issues: the conceptual model used by the designer(s) (or lack
>thereof!) and the decisions about what things to make easy for the
>programmer using the language.
>
>Both Perl and REBOL make it easy to use a "variable" -- you just start
>using it and the language keeps up with what you're doing; no advance
>declaration is required. OTOH Java makes it easy to detect errors in
>type mismatch as early as possible (at compile time), which REBOL and
>Perl can't catch until the program is running.
>
>Perl goes further and makes it easy to use data structures; if you try
>to modify/store data, the appropriate "place" is automagically created
>(and initialized to an appropriate value, depending on the operation
>you are performing). The Perl expression
>
> ++$array[$n]
>
>means "add one to the nth element of array". If the array doesn't have
>n elements (or if the array doesn't even exist!), Perl will allocate
>that position and and initialize it to zero before evaluating your
>expression.
>
>REBOL seems to occupy a middle-ground position on this issue; it does
>not require you to declare the existence of a data structure (as e.g.
>Java does) but it *does* require that you allocate and initialize it
>explicitly.
>
I think, that you are describing *only* a top-down approach here. A
bottom-up approach might lead to:
get-value: function [
{
get an element of a numeric array using zero-based index,
default value is zero
}
array [block!]
index [integer!]
] [value] [
value: pick array index + 1
either value [value] [0]
]
set-value: func [
{
set element of a numeric array using zero-based index,
default value is zero
}
array [block!]
index [integer!]
value [number!]
] [
insert/dup tail array 0 index + 1 - length? array
poke array index + 1 value
]
inc: func [
{
increment an element of a numeric array using zero-based index,
default value is zero
}
array [block!]
] [
set-value array index 1 + get-value array index
]
> REBOL certainly has some nice built-in facilities for
>processing series data, but once you leave those you are *really* on
>your own.
>
In Rebol you can "teach" the language to do what you want it to, because
Rebol facilitates the process of the language extension.
>Language design decisions have far-reaching (and often subliminal)
>effects on the subsequent design thinking of programmers using the
>language(s) in question. One such issue that I find interesting is
>the question of when I -- as the programmer -- must commit to a
>decision regarding the data structures used within my programs.
>
>COBOL and Pascal require that I commit to the type and size of every
>array before submitting my programs to the compiler, and initialize
>the structures appropriately (at run time, but before any other use).
>Java requires me to commit to the type of an array, but lets me defer
>the size committment until run-time when I actually initialize it.
>Newer versions of Java provide the Vector class, which can be thought
>of as an array that can change size during use. Perl and REBOL (and
>Python, et cetera) arrays/blocks not only let me dynamically resize
>during use, I don't even have to commit to a single type of data to
>put there! Finally, (back to the original discussion) Perl will even
>automatically figure out when to allocate/initialize structures and
>elements for me.
>
What if you needed a different default value, wouldn't that leave you on
your own in Perl?
>Advocates of each of these languages will offer passionate arguments
>for why the binding-time choices of their preferred language are good.
>As a polyglot, I'm less interested in picking sides in a political
>debate than understanding deeply the effects on my own thinking when
>I begin to "think like a native" in one or more of them.
>
>-jn-
>
I think, that the "effect on thinking" in Rebol may be caused more by
inertia than by language limitations.
-L
