World: r3wp

And it's important to have as many datatypes as possible for dialects.

I know. I just thought, that money (better let's call it currency), 
is just another unit ...

$ is used as a sigil of money in many countries, not just the US.

OK, so give me BCD! type then. I will not do make money! just because 
I want some precision. That reads badly ...

IIRC there was a blog what to do with money! datatype, and if the 
datatype should be more "complex". That is still not resolved.

In school, units were always encased in [], such as 5 [m / s]. I 
think it's possible to do something similar in REBOL.

More complex
 = "like R2". He was asking about restoring the unit prefix.

could a serialized item be considered its own datatype?, such as 
#[none]

I do not understand your question

I'm not sure it makes sense anyway. :-) I guess it's about how the 
scanner interprets certain characters and from that works out the 
datatype, and what limitations there are in detection.

Henrik probably wanted to introduce new form to REBOL's parser: 100[m 
/s]

There are a few serialized keywords, but the rest are constructors.

but then he realised, that we have already #[none] for serialisation 
... but I can be wrong ...

Pekr, yes, although [] directly, won't work. I'm assuming that we 
could basically do something like ![m / s] or &[m / s] and have that 
work as a datatype.

or ~[m / s]

good one

Will something like that work with user types? Can I define its "lexical 
form" (?) so that REBOL parser would accept that?

User types won't be able to affect the lexer.

So how REBOL identifies my user type?

MAKE or serialized forms, I expect.

constructors: I guess, that it is actually "nonstandard" to call 
#[...] representations "constructors", since they actually aren't 
"methods used to create instances of...", in fact, they actually 
aren't "methods", but rather "textual representations"

They are constructors internally, as you describe - try doing a bad 
one and read the error message.

BrianH: but I somehow have to distinguish usertype from e.g. decimal? 
So how do I do it? And how does REBOL's interpreter know it is mytype? 
How do I match it in parser for e.g.? Any example?

And they aren't textual representations - the data inside the serialized 
representation is REBOL data, not raw text.

the error message is: "** Syntax Error: Invalid construct -- #[**" 
how does that tell it is a method?

and, BTW, "construct" and "constructor" does not have the same meaning 
for me

Between that and conversations with Carl, it has become apparent 
that deserialization is done on a type-specific basis, and that the 
supported types have internal chunks of code that handle the data 
in the representations. You are being too specific in your definition 
of "constructor" - even in the OOP languages it means "something 
that constructs".

The internal code is something like MAKE or TO - type-specific.

Wikipedia: Constructor (computer science), a special method used 
in object oriented programming which puts the object's members into 
a valid state.

In REBOL, methods are called action! functions. Same principle, different 
implementation.

MAKE and TO are constructors too.

MAKE and TO: they can be called "methods", since they are functions, 
but #[...] is something totally different, and it surely isn't "a 
method"

Internal, remember?

there is nothing like "internal" from a user's POV, anything "internal" 
should be invisible, that is why I honestly don't understand, why 
the END! datatype is exposed

Not all the actions are exported as action! functions - some are 
only called by native code, like the action that handles function 
eval.

I was talking about an internal action, not something exposed.

moreover, the #[...] constructs are actually executed by the LOAD 
function (or maybe Transcode,...) internally, which may call whatever 
functions it likes to construct any specific datatype represented 
by the discussed #[...] text, but this does not make the "#[...]" 
text a function, anyway

Except the deserialization actions are exposed, indirectly. Not as 
action! functions - they are called by TRANSCODE, TO-BLOCK, ...

The text is not a function. The *handler* for the text is a function.

yes, but then the methods are Transcode, To-block, etc. the #[...] 
texts are only data for them

so, the distinction is, that "#[...]" actually is data (argument/arguments) 
for a constructor, not a constructor

TRANSCODE calls the action. I am talking about internal code here.

And it's not text - bug#864 proved that.

yes, I understand, there is a constructor (there has to be one), 
but the "#[...]" text is not a constructor, just data for a constructor

Ladislav, if you think that I am saying that the lexical form #[...] 
is a function call, you are wrong. I am saying that the processing 
of that lexical form is handled by an internal function call that 
constructs a value of a particular datatype. That is what I have 
always beenn saying.

And since then I have been trying to clear up that misunderstanding.

yes, that is correct, of course. What I mean by saying, that #[...] 
is not a constructor is, that the function is "somewhere else" (in 
C or internal Rebol code, I do not exactly mind in this case)

Well, the function "somewhere else" is all that I have been talking 
about, not the lexical form.

BTW, what do you think about the END! datatype? is there really a 
reason, why it has to be "exposed"?

There is a reason to reserve it, but not expose it per-se. It would 
need to be used by internal code and a lot of that internal code 
is written in REBOL in R3. From what I know about blocks (minimal), 
it seems like the nul character for C strings, but less required.