[mdosnov2016]

Hello,
is there any way to modify the foreach variable from within the foreach body?
e.g.

Code: Select all

foreach Y = std::fromTo(1, 100) do
 <command to change the value of Y>

I need to re-start the loop with different begin and end values, and I cannot
implement this without recursion.
Michael

[Paul Cerkez]

I don't remember if it exists in VIP or not but how about a "while" loop instead of a foreach?

pseudo code:

Code: Select all

Y = 1
While Y < 100,
   <do steps>
   < change value of Y (either increment by 1 or set to 100)> 
End While.

in pseudo VIP:

Code: Select all

...
Y=1,
MyWhileLoop(Y, Omega), % Omega is the upper limit)
.... 
 
MyWhileLoop(Y, Omega):-  %This is your 'while' loop
   Y<Omega, !,
  <do steps>
    MyWhileLoop1(Y, Omega, NewOmega),
    ...
MyWhileLoop(Y, Omega). 
 
MyWhileLoop1(Y, Omega, NewOmega):-  % this is the looping 'control' (value of Y)
     <do condition check for terminating>
      !,
      NewOmega = Y,
      MyWhileLoop(Y, NewOmega ). 
 
MyWhileLoop1(Y, Omega, NewOmega):-
      NewY = Y +1,
      NewOmege = Omega,
      MyWhileLoop(NewY, NewOmega). 

[mdosnov2016]

I know how to do recursion, thank you.
The problem with recursion is that it eats up the whole of my stack.
The problem is not with tail-recursive predicates, but with others
that call each other thousands of times...
b.r. Michael

[Paul Cerkez]

sorry, missed the implied cannot use recursion.

Deferring to Thomas.

[Paul Cerkez]

Michael,

dumb question. I'm confused.

Are you trying to restart the same foreach() loop from within the foreach() loop but with new start and stop numbers based on a action/decision within that loop?

<clause>:-
... steps ...
foreach(), %change the iterations of this loop and restart just the loop from within
end foreach.
... more steps ...
<end clause>.

OR,
are you just trying to stop the loop 'early' once a condition is met?

I get both possibilities when reading your initial post.

[Thomas Linder Puls]

What you are asking for is impossible. "Green" variables are not modifiable.

Furthermore std::fromTo(...) nondeterministically returns a sequence of numbers, it does not look at the current value of Y to find the next value.

[Paul Cerkez]

Thomas,
The std::fromTo() 'sets' the next value of 'Y' from the sequence each time though, correct?

[Thomas Linder Puls]

Yes, that is what I mean by "nondeterministically returns a sequence...". I.e. it returns one value at the time nondeterministically.