Just another update

Task/Parsing-RPN-calculator-algorithm/VBA/parsing-rpn-calculator-algorithm.vba

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+Global stack$
+
+Function RPN(expr$)
+Debug.Print "Expression:"
+Debug.Print expr$
+Debug.Print "Input", "Operation", "Stack after"
+
+stack$ = ""
+token$ = "#"
+i = 1
+token$ = Split(expr$)(i - 1) 'split is base 0
+token2$ = " " + token$ + " "
+
+Do
+    Debug.Print "Token "; i; ": "; token$,
+    'operation
+    If InStr("+-*/^", token$) <> 0 Then
+        Debug.Print "operate",
+        op2$ = pop$()
+        op1$ = pop$()
+        If op1$ = "" Then
+            Debug.Print "Error: stack empty for "; i; "-th token: "; token$
+            End
+        End If
+
+        op1 = Val(op1$)
+        op2 = Val(op2$)
+
+        Select Case token$
+        Case "+"
+            res = CDbl(op1) + CDbl(op2)
+        Case "-"
+            res = CDbl(op1) - CDbl(op2)
+        Case "*"
+            res = CDbl(op1) * CDbl(op2)
+        Case "/"
+            res = CDbl(op1) / CDbl(op2)
+        Case "^"
+            res = CDbl(op1) ^ CDbl(op2)
+        End Select
+
+        Call push2(str$(res))
+    'default:number
+    Else
+        Debug.Print "push",
+        Call push2(token$)
+    End If
+    Debug.Print "Stack: "; reverse$(stack$)
+    i = i + 1
+    If i > Len(Join(Split(expr, " "), "")) Then
+        token$ = ""
+    Else
+        token$ = Split(expr$)(i - 1) 'base 0
+        token2$ = " " + token$ + " "
+    End If
+Loop Until token$ = ""
+
+Debug.Print
+Debug.Print "Result:"; pop$()
+'extra$ = pop$()
+If stack <> "" Then
+    Debug.Print "Error: extra things on a stack: "; stack$
+End If
+End
+End Function
+
+'---------------------------------------
+Function reverse$(s$)
+    reverse$ = ""
+    token$ = "#"
+    While token$ <> ""
+        i = i + 1
+        token$ = Split(s$, "|")(i - 1) 'split is base 0
+        reverse$ = token$ & " " & reverse$
+    Wend
+End Function
+'---------------------------------------
+Sub push2(s$)
+    stack$ = s$ + "|" + stack$ 'stack
+End Sub
+
+Function pop$()
+    'it does return empty on empty stack
+    pop$ = Split(stack$, "|")(0)
+    stack$ = Mid$(stack$, InStr(stack$, "|") + 1)
+End Function