World: r3wp

Anton, are you sure, I don't get a 4 byte float?

>> d: make struct! [v [float]] none
>> d/v
>> type? d/v
== decimal!
>> length? third d
== 4

The length of a decimal is 8.

missed a line:

>> d/v
== 0.0

... no longer sure ...! :-)

My error, sorry.

http://www.rebol.com/docs/library.html#section-4.2

d: make struct! [v [decimal!]] none
i: make struct! [v1 [integer!] v2 [integer!]] none

i/v1: to integer! (random 2 ** 32) - (2 ** 31) - 1
i/v2: to integer! (random 2 ** 32) - (2 ** 31) - 1

change third d third i

The random decimal is d/v

Now divide by max-decimal (whatever that is) and multiply by desired 
range (eg. pi).

:-) I follow you, when you say, you're no longer sure. This is a 
little used corner of REBOL (for me at least).


I think, we have a problem still. random 2 ** 32 seem to never give 
results above 2 ** 31.

Never returns:

>> until [a: random 2 ** 32 a > (2 ** 31)]

That would be a problem, yes.

And since we don't have a 16 bit datatype (or maybe we do with a 
string or other series somehow!?), we have to make 8 times random 
256 (and subtract 1).

We can substitute the struct of 2 integer!s with a struct of 8 char.
Maybe this is useful:
>> random 255.255.255.255.255.255.255.255
== 168.97.60.251.15.20.205.31

Kib asked a simple question about random and decimals. It seems to 
be a bit of a hazzle to get what we want, and this should be pointed 
out to Carl for R3, I think.

but can't put tuple! in struct directly...

Sometimes I wonder why such simple things are not implmented natively 
in REBOL.

Kib, I think, the answer is, that REBOL do a lot and then some more, 
but there are a few holes.

Yes, this one and repeating a string are essential to me. I may find 
other cases too :)

random also doesn't return 0.

(ah.. that's why you subtracted 1, never mind.)

The other thing I was thinking we might need to watch out for is 
the production of invalid decimals. Maybe some mantissa combinations 
are not valid?

:-)

Kib, feel free to ask questions about all this. It may easily get 
blurred, when we talk like this. And it shows you, that we're often 
in doubt, because REBOL is so deep. (I hope, it's ok, we do this 
in the Rebol School group.)

Right, Anton, I forgot about that.

Let's switch to the Math group.

Maybe the invalid decimal can be handled with some: if error? try 
[...]

Kib, there might be a good explanation, why there's no random decimal 
in REBOL. See:

http://stackoverflow.com/questions/439115/random-decimal-in-python
It's not a trivial problem.

You asked how to make a random number between e.g. pi and -pi. There 
are a number of ULPs (Unit in the Last Place) between those two numbers. 
For 64 bit decimals, it's a large number. The possible decimals in 
computer arithmetic lie closer together around zero than for large 
numbers. If you had a routine, that would give you any possible 64 
bit decimal number between pi and -pi with equal probability, then 
you would get a lot more numbers close to zero than close to either 
pi or -pi. The distribution wouldn't be flat (as you would expect).


It's much better to choose, how many different values between pi 
and -pi, you need, and then make a random integer of that number, 
and do some calc to get the result between pi and -pi.

I hope, it makes sense.

I came with this, what do you think of it ? (highly criticable) :

random-dec: func[i n /local ent dec] [
    "generates a decimal : i digits before, n digits after"
    ent: to-integer random i
    dec: to-integer random n
    return to-decimal rejoin [ent "." dec]
]

print random-dec 9999 999999 ; 4 digits before 6 after

Or even :

random-dec: func[i n /fromdigits /local ent dec] [
    "i digits before, n after"
    
    if fromdigits [
        "i: number of digits before, n: number of digits after"
        i: 10 ** i - 1
        n: 10 ** n - 1
    ]
    
    ent: to-integer random i
    dec: to-integer random n
    return to-decimal rejoin [ent "." dec]
]

print random-dec 999 99999 ; 3 digits before, 5 after
print random-dec/fromdigits 4 6 ; 4 digits before, 6 after

You shouldn't need the return statement.  The last value will be 
returned unless a return is found elsewhere.

Good work though Kib2.

Yes, an interesting approach. Just remember, that random 9 will return 
1-9, never zero. So maybe you wanna add one before doing the random, 
and then subtract one afterwards?


Another thing, you might wanna have those explanation strings in 
the variable block? Try:


>> random-dec: func ["i digits before, n after" i n /fromdigits "i: 
number of digits before, n: number of digits after"] []          
                          
>> ? random-dec

is there some builtin way by which I can format number like this 
11231  => 11.231 ?

(I have done it)

nice

REBOL allow thousand separation with ', like: 11'231, but it's only 
for readability. You would probably convert to string and put #"." 
in for nice output.

GEomol, yes I need it for nice output ... this is the function I 
made:
format-int: func [ int ] [ 
	a: to-string int

 d: tail a loop to-integer ((length? a) - 1) / 3 [ d: back back back 
 d  insert d "," ]
	head d
]

Cool!

well, it's not the nicest function probably but I am tired and just 
need it to work

Well, it does work, so you can be happy! :-)

There's nothing built in to do that Janko.

Gabriele once wrote a function for this. I can't remember if it's 
called pad-decimal or form-decimal.

Yes, there are a number of them out there.

add-seps: func [
        "Insert group separators"
        str [any-string!]
        /with sep [string! char!]
        /reb "Use REBOL group separator"
    ][
        sep: any [sep all [reb #"'"] #","]
        str: skip any [find str "."  tail str] -3
        while [not head? str] [
            insert str sep
            str: skip str -3
        ]
        str
    ]

Simple Question: I want to assign a specific script name to the word 
RUN and have it execute it whenever I type it into the console.
RUN: do %script.r

But upon the assignment, it evaluates the expression and executes 
it.  So I tried it in a block as RUN: [do %script.r]
but this returns == [do %script.r]


I can do this: IT: %script.r    and then type DO IT to perform the 
script, but I want a way to combine the DO and the IT together.  
Any ideas?

run: does [do %script.r]

Isn't RUN already a native function ?

Thank you Paul.  Perfect.

Yes, RUN is native, but you can redefine it, if you like.

Yes it is but I don't believe it is of any use.