Re: [If/then and sequences...]
Hawke,
*Very* interesting. I was *going* to ask:
In
> return (data >=13) and (data <=19)
why don't you have to *build* a sequence from a series of logical ands
working on each element of the data sequence in order to have that boolean
data returned in a sequence?? It certainly works, but how?
but then I read the manual (!) & saw that:
"When applied to a sequence, a unary (one operand) operator is actually
applied to each element in the sequence to yield a sequence of results of
the same length. "
Nifty.
Dan
wearing a dunce cap
----- Original Message -----
From: "Hawke'" <mikedeland at NETZERO.NET>
To: <EUPHORIA at LISTSERV.MUOHIO.EDU>
Sent: Wednesday, August 30, 2000 4:29 AM
Subject: Re: [If/then and sequences...]
> From: Derek Parnell <derekp at SOLACE.COM.AU>
> > In a lot of programming languages, the operators '<', '>' and '=' always
> > return a boolean result - that is either TRUE or FALSE.
> in most languages, actually, you dont have sequences, and its not allowed
> to perform the actions that we do in euphoria, that are oft taken for
> granted,
> upon entire arrays...
> unless u go thru painstaking for loops examining every array element...
>
> eg:
> sequence ages, teens
> ages = {10,20,22,12,32,55,34,23,15}
> function IsTeenager(sequence data)
> return (data >=13) and (data <=19)
> end function
> teens = IsTeenager(ages)
>
> now u have a nice neat list of 0's and 1, in a sequence, showing u the
> indexes of all the teenagers, and the find() command will neatly locate
> those indices...what could be simpler?
>
> try that in pascal or C, and you are looking at for loops, bunches of
> temporary storage array/variable declarations, and many lines of code...
>
>
> >What you've demonstated is that in Euphoria, these operators return
> >a boolean when both operands are atoms, and return a sequence
> >when either operand is a sequence
> ERRRRRRRRRRRRR
> it returns a sequence OF booleans, that matches the original size and
depth
> of the original sequence
> atoms beget a single 'atomic' boolean result
> sequences beget a sequence of boolean results...
> seems logical to me :)
>
> > (unless the operand is used in an IF statement, in which it is illegal).
> because there is no way to determine WHICH boolean within the sequence
> you want to look at...
> if u SPECIFY which boolean you want to look at within a sequence, by
> referencing it SPECIFICALLY, then it works just fine...
>
> eg: same as above
> if ages = 12 then puts(1,"almost a teenager") end if
> like...DOH, wont work...which person are you talking about???????
>
> if ages[3] = 12 then puts(1,"almost a teenager") end if
> well kick butt! now we know what person we are talking about, and
> everything is kosher and still maintains absolute logicality....
>
>
> >And that compare() function always returns an atom
> of course, because we need a method which will allow sorting...
> all compare() does is recursively analyze the results of a boolean
> logic operation which was recursively applied to a sequence,
> just like the example above, and neatly sends back a singular
> boolean result instead of the list of results.
> saves us having to actually thread a for loop or a find() function...
> does it faster usually too cuz rob can take shortcuts...
> and in reality, its more like a tri-state boolean that gets returned, not
an
> atom...
>
>
> >(and equal() function always returns a boolean)
> function equal(object a, object b)
> return compare(a,b) = 0
> end function
> that's all rob is doing...it was an include to the core language for
> conveince
> sake, nothing more, nothing less....it makes code a touch cleaner, and
> everyone
> was always putting that function i just wrote into their code toolbox
> anyway...
> saves a wee typing...shrug...no magic here
>
> >In my mind that is inconsistent and also not simple.
> function IsTeenager(sequence data)
> return (data >=13) and (data<=19)
> end function
> what is not simple about that function ????
> where is the inconsistency???
> seems quite clear and consistent to me?!?!?!?!
>
> > Its just that from my point of view, it would have been more intuitive,
> and
> > simpler, to reverse this arrangement of Robert's. That is, have the '<',
> > '>', and '=' operators always return a boolean (and allow their use in
> IFs),
> > and have the compare() function return a sequence.
> wanna try writing IsTeenager useing that proposed method???
> and have it return a list of boolean values that are exactly nested
> as the passed sequences??????
>
> something like this i suppose???
>
> function IsTeenager(object data)
> if atom(data) then return data end if
> for i = 1 to length(data) do
> if sequence(data[i]) then
> data[i] = IsTeenager(data[i])
> end if
> if (data[i] >= 13) and (data[i]<=19) then
> data[i] = 1
> else data[i] = 0
> end if
> end for
> return data
> end function
>
> hrmmmm, not so clear now????
>
> hell, i aint even sure that's a fully perfect function to do the task...
> i aint tested it, and i would have to test it to make sure it works...
>
> but i ***KNOW*** from just looking at it, without a doubt,
> what the following code does:
> function IsTeenager(sequence data)
> return (data >=13) and (data<=19)
> end function
>
> shrug, i prefer knowing with a glance what code does...
> and the second function really looks a lot less complicated to me...
>
> >This probably would have
> >made the equal() function redunant. Of course its WAY too late to
introduce
> >this sort of change to the language, and I'm not advocating that. I'm
just
> >wondering why Robert decided to arrange the language the way he did.
> see above????
>
>
> > Current:
> > Operation Operands Allowed in IF Result
> > -------------------------------------------------------------------
> > =/>/< atoms yes boolean
> > =/>/< sequences no sequence
> errrr NO....
> that should read:
> =/>/< sequences no (without proper referenced indicies)
sequence
> of booleans
>
> > =/>/< mixed no sequence
> what is 'mixed'?????
> we have no 'mixed' data type in EU...
> it is an integer, an atom, a sequence, or an object...
>
> > compare() atoms yes atom
> > compare() sequences yes atom
> > compare() mixed yes atom
> errrrr more properly, that would be
> compare() atoms yes tristate boolean
> ditto for sequences....logical and consistant
>
> > equal() atoms yes boolean
> > equal() sequences yes boolean
> > equal() mixed yes boolean
> tis only a shortcut for typing, as per above, and does no magic...
>
> > if atom yes boolean
> > if sequence no n/a
> as per above, u cannot determine WHICH part of the sequence
> you are looking at without telling the interpreter which part of
> the sequence you are referring to...
>
> to sum up, EU's grace and elegance comes from the
> manner rob has defined the language as it stands...
>
> lets suppose you want a function that examines any valid
> pair euphoria objects, atoms or sequences, no matter how big or
> nested they might be and determines which of them is the
> smallest, or the minimum, persay...
> to wit:
> constant
> first ={10,20,30,20,10},
> second={20,10,40,10,20}
> sequence result
> result = minimum(first,second)
> --result would now be = {10,10,30,10,10}
>
> a function like this is extremely handy for fuzzy logic and
> graphics applications
>
> the function to do this was written long ago with one line
> of euphoria code, and is as simple and elegant as they come
> (by lucius i believe)
> function minimum(object a, object b)
> return a*(a<=b) + b*(b<a)
> end function
>
> i dont believe it gets much simpler or clearer then this in a language...
>
>
> if you really really MUST have your greater() and lesser() functions
> then try these:
>
> function greater(object a, object b)
> return compare(a,b) = 1
> end function
> function lesser(object a, object b)
> return compare(a,b) = -1
> end function
>
>
> problem solved?????
>
> hope this helps clear things up as to why EU does things the way
> it does, and further elaborates on Irv's post as to why things
> function they way they do in EU...
>
> --Hawke'
>
>
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