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Methods to solve scripts with cell references (up/down dependancy and circular reference detection)

Posted on 2015-01-28
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Last Modified: 2015-02-01
Dear Experts,

I´ve been developing a parser/interpreter in Delphi to solve scripts which use functions and variables located in cells (for the while only in lines and using one single column). I´m using this to create a list of input parameters and calculated parameters.

The parser is doing very well, but the approach to update values in the cells uses a top to bottom update. In this case, bottom cells can only use top variables.

Thinking about extending this list to more columns and to allow top cells to use bottom variables, which method (algorithm) could I use to correctly update all cells ? I am also not figuring how to detect circular reference out.

I´ll appreciate any help on this. Thanks.
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Question by:engiLAB
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ambience earned 500 total points
ID: 40577059
One algorithm could be like this.

Q = queue of all variables
S = empty stack
H = empty hashtable

while stack is empty 
{
  hashsize = size of H
  while not queue is empty 
  {
      V = pop variable from list
      if canBeCalculated(V):
        calculateValue(V)
        push V on H
      else
        push V on stack
  }
  
  if hashsize equals size of H: // Nothing got calculated!!!
    throw CycleException
    
  if stack is empty:
    print DONE!
    return
    
  pop all from S into Q
}
       

function canBeCalculated(v)
{
  if V's expression is constant:
    return true
  if all dependent variables of V are in H:
    return true
}

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