Whenever I'm home alone, I like to let my mind wander and think about Excel formulas in POI. (do I need to get a life? perhaps, but my wife says we can't afford it right now)
So I've been thinking on how we might implement formulas: two stacks and a list operators operands results For Formula -> RPN-tokens Example walkthough of algorythm As you move through the formula poke the operation on the operation stack and read via PEMDAS order until your done, for every operation determine the number of operands you need and grab them. In the event of 3 + 3 + 4 : since there are no parenthesis, you'll take the first operand, tokenize and plug it onto the stack, next the + operation: tokenize and plug it on to the operation stack, find the next operand and plug it onto the operand stack. You've got a queued operation so you move the tokens over to the results list in operand,operand,operation order. ---- 3 * (3 + 4) You find a 3 tokenize and shove it onto the operands, a * tokenize and shove it onto the operators stack, see the ( next so you shove it onto the operations stack, see the 3 tokenize and shove it onto the operands stack, see the + tokenize and shove it onto the operations stack, see the 4 and put it onto the operands stack, see the ) You pop off the next operation, the +, it takes two so you throw the two operands to the results list followed by the operation, you pop the next operation which is the open parenthesis so you throw only the closed parenthesis onto the results stack (one token for both), you pull the next operation, discover its binomial, the last thing you did was a parenthesis so you don't need two operands, you just shove the remaining operand onto the results list and the operation along with it. thoughts? -- For RPN -> Formulas Start at the left and just move right, any place there are parenthesis engulf it and move out. Same basic method in reverse, only hard thing is we'll have WAY MANY MORE possible correct things. Lets not support legacy stuff (stuff excel won't write in new sheets) for this release at least. -Andy -- http://www.superlinksoftware.com http://jakarta.apache.org/poi - port of Excel/Word/OLE 2 Compound Document format to java http://developer.java.sun.com/developer/bugParade/bugs/4487555.html - fix java generics! The avalanche has already started. It is too late for the pebbles to vote. -Ambassador Kosh
