[REBOL] Re: Is a "series" aka an "array"
From: moliad:gm:ail at: 27-Nov-2010 3:56
Rebol as a language is so richly typed that what you would normally
program as strings, arrays or numbers in other languages, you can do
with human understandable datatypes in Rebol (dates, html tags, etc).
pseudo types allow you to use several types as a concept rather than
having to support each one individually.
Gabriele gave you an example for function arguments which is widely
used, here is another example which shows how useful pseudo types can
be:
>> find [ 1x1 11.22.33 "2" #2 2 <2> 2.0 ] number!
== [2 <2> 2.0]
>> find [ 1x1 11.22.33 "2" #2 2 <2> 2.0 ] series!
== ["2" #2 2 <2> 2.0]
you see that the first find really found the first number in the
block, whereas the second returned the first series it found.
going a bit further, I'll point out that to be considered a series, a
datatype must contain an index. in the traditional sense, an array
doesn't have an embedded index.
so for example:
>> a: skip [ 1 2 3 4 5] 2
== [3 4 5]
>> index? a
== 3
if we refer to the find example above, you will notice that it skipped
both the pair! and tuple! datatypes... this is because they are
neither numbers nor series. why? they aren't a single value, but they
also do not have an index.
so although you can do:
>> second 11x22
== 22
you cannot do:
>> a: skip 11.22.33 1
** error ** skip expected series ...
these two actually fall into another pseudo-type! scalar!
>> scalar? 11.22.33
== true
>> scalar? 11x22
== true
>> scalar? 1
== true
so if we attempt the find above with scalar! (only works in R3) ... we get:
>> find [ 1x1 100.20.300 "2" #2 2 <2> 2.0 ] scalar!
== [2 <2> 2.0]
(in R2, scalar! is not really a pseudo type, but just a block! which
holds all scalar types. this was fixed in R3).
hope this helps! :-D
-MAx
