--- src/scratchpad/src/org/apache/poi/hssf/record/formula/functions/Replace.java	(revision 605370)
+++ src/scratchpad/src/org/apache/poi/hssf/record/formula/functions/Replace.java	(working copy)
@@ -20,6 +20,93 @@ 
  */
 package org.apache.poi.hssf.record.formula.functions;
 
-public class Replace extends NotImplementedFunction {
+import org.apache.poi.hssf.record.formula.eval.ErrorEval;
+import org.apache.poi.hssf.record.formula.eval.Eval;
+import org.apache.poi.hssf.record.formula.eval.NumericValueEval;
+import org.apache.poi.hssf.record.formula.eval.StringEval;
+import org.apache.poi.hssf.record.formula.eval.StringValueEval;
+import org.apache.poi.hssf.record.formula.eval.ValueEval;
 
+/**
+ * An implementation of the REPLACE function:
+ * Replaces part of a text string based on the number of characters 
+ * you specify, with another text string.
+ * @author Manda Wilson < wilson at c bio dot msk cc dot org >
+ */
+public class Replace extends TextFunction {
+
+	/**
+	 * Replaces part of a text string based on the number of characters 
+	 * you specify, with another text string.
+	 * 
+	 * @see org.apache.poi.hssf.record.formula.eval.Eval
+	 */
+    public Eval evaluate(Eval[] operands, int srcCellRow, short srcCellCol) {		
+    	Eval retval = null;
+        String oldStr = null;
+        String newStr = null;
+        int startNum = 0;
+        int numChars = 0;
+        
+        switch (operands.length) {
+	        default:
+	            retval = ErrorEval.VALUE_INVALID;
+	        case 4:	        
+	        	// first operand is text string containing characters to replace
+	            // second operand is position of first character to replace
+	            // third operand is the number of characters in the old string
+	            // you want to replace with new string
+	            // fourth operand is the new string
+	            ValueEval firstveval = singleOperandEvaluate(operands[0], srcCellRow, srcCellCol);
+	            ValueEval secondveval = singleOperandEvaluate(operands[1], srcCellRow, srcCellCol);
+	            ValueEval thirdveval = singleOperandEvaluate(operands[2], srcCellRow, srcCellCol);
+	            ValueEval fourthveval = singleOperandEvaluate(operands[3], srcCellRow, srcCellCol);
+	            if (firstveval instanceof StringValueEval
+	            	&& secondveval instanceof NumericValueEval
+	            	&& thirdveval instanceof NumericValueEval
+	            	&& fourthveval instanceof StringValueEval) {
+	            	
+	                StringValueEval oldStrEval = (StringValueEval) firstveval;
+	                oldStr = oldStrEval.getStringValue();
+	                
+	                NumericValueEval startNumEval = (NumericValueEval) secondveval;
+	                // NOTE: it is safe to cast to int here
+	                // because in Excel =REPLACE("task", 2.7, 3, "est") 
+	                // returns test 
+	                // so 2.7 must be truncated to 2
+	                // and =REPLACE("task", 1, 1.9, "") returns ask 
+	                // so 1.9 must be truncated to 1
+	                startNum = (int) startNumEval.getNumberValue();
+	                
+	                NumericValueEval numCharsEval = (NumericValueEval) thirdveval;
+	                numChars = (int) numCharsEval.getNumberValue();
+	                             
+	                StringValueEval newStrEval = (StringValueEval) fourthveval;
+	                newStr = newStrEval.getStringValue();
+	            } else {
+	            	retval = ErrorEval.VALUE_INVALID;
+	            }
+	    }
+	        
+        if (retval == null) {
+			if (startNum < 1 || numChars < 0) {
+				retval = ErrorEval.VALUE_INVALID;
+			} else {
+				StringBuffer strBuff = new StringBuffer(oldStr);
+				// remove any characters that should be replaced
+				if (startNum <= oldStr.length() && numChars != 0) {
+					strBuff.delete(startNum - 1, startNum - 1 + numChars);
+				} 
+				// now insert (or append) newStr
+				if (startNum > strBuff.length()) {
+					strBuff.append(newStr);
+				} else {
+					strBuff.insert(startNum - 1, newStr);
+				}
+				retval = new StringEval(strBuff.toString());
+			}
+        } 
+		return retval;
+    }
+
 }