World: r3wp

thanks for the suggestions :-) I'm doing it differently now though...

The most elegant solution would be to patch layout so it accepts 
set-paths.

Speaking of double bind, I have no clue of the how-to to this clue. 
 In Ocaml we can make co-recursive definitions, also with negation. 
 But when I try this on Rebol, it claims the value before I have 
the time to define it:  a: not b and b: not a.   Interp: ** script 
error, b has no value.  What is the method ?  Or are we out of paradise? 
 I could use that as a form of loop, or a form of lexical closure 
to model some linguistic phenomenas.  But how?  We know the problems 
of complement of complement, but as a function value it should be 
feasible.

Do you have an example,  besides:
a: not b
b: not a

In rebol this are executed serially, so the first statement fails 
because b is not defined.

A pair number cant be defined without impair. pair is impair +1 and 
impair is pair +1.  So we have to define both at the same time.  
In logic, the negation is a function where true is false and false 
is true.  Not and complement are native to rebol.  If I try a: not 
'b b: not ''a. asking the value of a, :a, does not return not b but 
false.   Something like this does not seem to work.  What I want 
is criss-crossed functions one defined by the other.  In principle, 
Rebol being functionnal.   It should be simple, a one liner, but 
I am too newbee to find the elegant way to do this.

Normand, can you give us the actual code that is tripping you up 
here?  Perhaps with a look I could help you out...

Normand, seems you do not define functions, but executes the expressions 
directly?
pair: func[][impair + 1]
impair: func[][pair + 1]
the code makes no sense but rebol accepts it perfectly.

Normand: don't you mean this?:

odd?: func [i] [either i = 0 [false] [even? i - 1]]
even?: func [i] [either i = 0 [true] [odd? i - 1]]
odd? 11

warning: odd? and even? are already defined in Rebol, you might prefer 
to use names like pair? and impair? instead like you wrote above

Thanks for the answer.  I am aiming in the direction of corecursive 
types, to model a category thing.  So the following works.

Co-recursive types:
>> owed: func [x] [either paid? x [negate x][false]]

>> owed?: func [x] [either all [integer? x negative? x] [true] [false]]
>> paid: func [x] [either owed? x [negate x] [false]]

>> paid?: func [x] [either all [integer? x positive? x] [true] [false]]
>> a: 5
== 5
>> owed a
== -5
>> owed? a
== false
>> owed? b: owed 5
== true
>> a: paid b
== 5
>> paid? a
== true
>> paid? paid -5

Now I need custom types.

--Type inference from a newbee point of view:

What if I wanted to form true (but un-native) datatypes ?  To program 
them, I shall use the same method as other types in Rebol: 

To mention the type as its value : seasoning!: seasoning!, like the 
definition of the type money!: 'money.

Rather, I would like to do type inference as they do, for example 
in ML (I adapt the example from Felleisen's LittleMLer):

So I would need to define a new type and verify the type of a word 
with type?
seasoning!: ('salt or 'pepper)
Unfortunately this does not seems possible 
** Script Error: Cannot use or~ on word! value
** Near: 'salt or 'pepper
In Rebol:
>> source integer!
integer!: integer!
type? 1
== integer!
but
natural!: (0 or natural +1)
Type inference:
seasoning? salt
Would like the answer == seasoning
is-of-type? 'salt seasoning
Would like the answer == true

Am I forced to turn to Ocaml to do this?  I am stuck.  Thanks for 
any help!

I don't know exactly what you can accept and what not, but this will 
work:

seasonings: [salt pepper]


seasoning?: func [value [any-type!]] [found? find/only seasonings 
get/any 'value]
seasoning? 'salt

As far as I know it is not possible to define new types.


Not sure that would solve your problem anyway.  A word can point 
to a value that has only *one* type (ignoring the heirarchy -- eg 
block! is also series!). So complex assertions about something would 
not be easy.


Maybe rethink the need.....Use objects to hold both a value and a 
type:
>> item: make object! [value: 'salt type: 'seasoning]
>> item/type
== seasoning
>> 'seasoning = item/type
== true

You could encapsulate that in a couple of functions and expand the 
scope (maybe make type a block with multiple values)

Gabriele Santilli has made some custom types. I don't remember having 
fully understood how it works, so I can't tell you how he did it 
! But it can be found here:
http://www.colellachiara.com/soft/YourValues/libs/

custom-types.r is GPL.

(It's really very clever. :)

Just reading the code... Needs a demo.
custom-types.r  needs  standard-actions.r

I'll try to make one.

Hmm, there seems no easy way to make a demo. Gabriele is using an 
include mechanism (prebol.r I think) from the SDK . But it looks 
like
http://www.colellachiara.com/soft/YourValues/main.r
is the starting point.

Gabriele, if you're listening, the header of http://www.colellachiara.com/soft/YourValues/yourvalues.r
contains:
	File: %main.r   ; <-- should be %yourvalues.r   ??

Gosh, it's too hard for me to do in any reasonable time. I suggest 
looking at the code to figure out the method used, then see if you 
can make your own custom types.

Anton: the header is wrong because that file is generated with prebol 
using main.r

(a version of prebol with some minor modifications.)

about an example: there should be a complex.r in that dir that is 
a bit outdated (lacks support for molding and loading) but should 
be a good start. also template.txt is the starting point to create 
a new type.

you need to use starred actions on them though, i.e. add* instead 
of add, insert* instead of insert and so on, as well as make* and 
to*.

maybe somedaye i'll have the time to finish this stuff and add docs...

:) Now I think I remember I asked you that about the File: before 
sometime...

but, i'm not 100% sure Normand really needs this. custom types are 
not always the most elegant solution; actually, they are very rarely.

What are you up to these days anyway ?

also, i would really discourage a newbie from using that stuff as 
it is very experimental :-)

finishing the detective version 3, then (don't know if i can say 
that, so i won't.)

Why not ? :)

I wish I had some understanding of inference rules. Never studied 
Lisp stuff.

I think all those parens scared me away.

i don't think common lisp does any type inferencing.

That's how much I know. :)

and, i think an interpreted language would probably have a hard time 
at it, except for simple cases like the seasoning above.

which is elegantly solved as ladislav pointed out anyway.

the only advantage of having a real type in that case is type checking 
in fuction arguments; you don't get that with my custom-types (i 
don't think it is worth redefining FUNC etc. just for this), and 
it's not a big deal actually.

Are you actually using the custom types in any apps ?

i'm using something close (i.e. a very dumbed down and specialized 
version of it) in the backend for the portals for the Detective

basically the scripts interface to the mysql db via custom rebol 
values

I see.

I've just noticed a new global word PATH existing since View 1.2.10, 
an undocumented function.

--> rambo

About custom types: thats objects. they work like dynamic OO, no 
static typing and inferencing like ML

Thanks for all those suggestions.   I was out for quite a while and 
am very happy of all those remarks. It will help orient my trials&errs. 
 About  objects, dynamic versus static, If I understand it, in Rebol 
it is static?  I never had to use them except to encapsulate the 
whole of an app.  Is there a trick to mimick something dynamic to 
hold changing values?  Maybee a copied block is enough?  I wonder 
because I regularly try to add code to a bibliographic database, 
a kind of a variation on bibtex (never ended, allways in progress), 
And I am not too far from aiming the storage mechanism and wonder 
what I should use to hold something like from 5 to 10 thousand references 
(my actual need is 3.5K)  I used endnotes in the past, but dreamed 
about my own.  It is a lot of work (more than I expected as it is 
my first app).   Up to now I think I will use simply name-value pairs, 
like Carl's cardex.  This kind of data is more like a ragged array, 
the fields and their numbers allways vary, and I may amend their 
list with time.  The idea of using an object would be nice but need 
something where I may add or retract variable names and change their 
values.  By the way, I thank Volker for his edit-tools, that may 
help to add a writing pad.  And his double slider is refreshingly 
new for such and old paradigm as an editor.