September 2017 Update

Task/Parsing-Shunting-yard-algorithm/Xojo/parsing-shunting-yard-algorithm.xojo

@@ -0,0 +1,170 @@
+Function ShuntingYard(strInfix As String) As String
+
+
+  Dim i as Integer
+  Dim token, tokenArray() As String
+  Dim stack(), queue() As Variant
+  Dim discard As String
+  Dim op1, op2 As String
+
+  Dim Left_Brackets, Right_Brackets As Integer
+
+  Dim output As String
+  Dim dbl_output As Double
+
+
+  Left_Brackets = CountFields(strInfix, "(")
+  Right_Brackets = CountFields(strInfix, ")")
+
+  If Left_Brackets = Right_Brackets Then
+
+
+
+    'Get tokens
+    tokenArray = Split(strInfix," ")
+
+
+
+    'Initialize array (removed later)
+    ReDim stack(1)
+    ReDim queue(1)
+
+    'Loop over tokens
+    For i = 0 to tokenArray.Ubound
+
+
+    'i = i + 1
+      If i  > UBound(tokenArray) Then
+        Exit For
+      Else
+        token = tokenArray(i ) 'i-1 due to Split returning a Base 0
+      End If
+      If token = "" Then
+        Exit For
+      End If
+
+
+
+
+
+
+      Dim stackString As String
+      Dim queuString As String
+
+      for m as Integer = 0 to stack.Ubound
+        stackString = stackString +  " " +  stack(m)
+      Next
+
+      for m as Integer = 0 to queue.Ubound
+        queuString = queuString + " " +  queue(m)
+      Next
+
+      MsgBox(Str(i) + "      " + token + "      " + stackString + "      " + queuString)
+
+      'Window1.txtQueu.Text = Window1.txtQueu.Text + Str(i) + "      " + token + "      " + stackString + "      " + queuString + EndOfLIne
+
+
+
+
+      ' If-loop over tokens (either brackets, operators, or numbers)
+      If token = "(" Then
+        stack.Append(token)
+
+      ElseIf token = ")" Then
+        While stack(stack.Ubound) <> "("
+          queue.Append(stack.pop)
+        Wend
+
+        discard = stack.Pop 'discard "("
+      ElseIf isOperator(token) Then
+        op1 = token
+
+
+        //Do While (isOperator(Peek(stack)))
+        While isOperator(    stack(stack.Ubound)  ) = True
+          op2 = stack(stack.Ubound)
+          If op2 <> "^" And precedence(op1) = precedence(op2) Then
+            '"^" is the only right-associative operator
+
+            queue.Append(stack.pop)
+
+          ElseIf precedence(op1) < precedence(op2) Then
+            queue.Append(stack.Pop)
+          Else
+            Exit While
+          End If
+        Wend
+        //Loop
+
+
+        stack.Append(op1)
+      Else   'number
+        'actually, wrong operator could end up here, like say %
+        'If the token is a number, then add it to the output queue.
+        queue.Append(CStr(token))
+      End If
+
+
+
+
+    Next
+
+
+
+    for i = 0 to queue.Ubound
+      output = output  +queue(i) + " "
+    next
+
+    for i = stack.Ubound DownTo 0
+      output = output + stack(i)+" "
+    next
+
+
+
+    While InStr(output, "  ") <> 0
+      output = ReplaceAll(output,"  "," ")
+    Wend
+
+
+    output = Trim(output)
+
+
+    Return output
+
+  Else
+
+    MsgBox("Syntax Error!" + EndOfLine + "Count left brackets: " + Str(Left_Brackets) + EndOfLine +"Count right brackets: " + Str(Right_Brackets))
+
+  End If
+
+End Function
+
+
+Function isOperator(op As String) As Boolean
+
+  If InStr("+-*/^", op) <> 0 and Len(op) = 1 Then
+    Return True
+  End If
+
+End Function
+
+
+Function precedence(op As String) As Integer
+
+  If isOperator(op) = True Then
+
+
+
+    If op = "+" or op = "-"  Then
+      Return 2
+    ElseIf op = "/" or op = "*" Then
+      Return 3
+    ElseIf op = "^" Then
+      Return 4
+    End If
+
+
+  End If
+
+
+End Function