Data update

Task/Parsing-Shunting-yard-algorithm/FreeBASIC/parsing-shunting-yard-algorithm.basic

@@ -0,0 +1,121 @@
+Dim Shared As String stack, queue, token
+stack = ""
+queue = ""
+token = "#"
+
+Function word_(s As String, n As Integer, sep As String = " ") As String
+    Dim As Integer pio, cnt, posic, i
+
+    pio = 1 : cnt = 0 : posic = 0
+    For i = 1 To Len(s)
+        If Mid(s, i, Len(sep)) = sep Then
+            cnt += 1
+            If cnt = n - 1 Then pio = i + Len(sep)
+            If cnt = n Then posic = i: Exit For
+        End If
+    Next
+
+    If cnt < n Then Return ""
+    If posic = 0 Then posic = Len(s) + 1
+
+    Return Mid(s, pio, posic - pio)
+End Function
+
+Sub stackPush(s As String)
+    stack = s & "|" & stack
+End Sub
+
+Sub queuePush(s As String)
+    queue = queue & s & "|"
+End Sub
+
+Function queuePop() As String
+    Dim As String result = word_(queue, 1, "|")
+    queue = Mid(queue, Instr(queue, "|") + 1)
+    Return result
+End Function
+
+Function isOperator(op As String) As Boolean
+    Return Instr("+-*/^", op) <> 0 And Len(op) = 1
+End Function
+
+Function precedence(op As String) As Integer
+    If isOperator(op) Then
+        Return 1 + (Instr("+-*/^", op) <> 0) + (Instr("*/^", op) <> 0) + (Instr("^", op) <> 0)
+    End If
+End Function
+
+Function stackPop() As String
+    Dim As String result = word_(stack, 1, "|")
+    stack = Mid(stack, Instr(stack, "|") + 1)
+    Return result
+End Function
+
+Function stackPeek() As String
+    Return word_(stack, 1, "|")
+End Function
+
+Function reverse(s As String) As String
+    Dim As String result = ""
+    Dim As String token = "#"
+    Dim As Integer i = 0
+
+    While token <> ""
+        i += 1
+        token = word_(s, i, "|")
+        result = token & " " & result
+    Wend
+
+    Return result
+End Function
+
+Dim As String test = "3 + 4 * 2 / ( 1 - 5 ) ^ 2 ^ 3"
+Print !"Input:\n"; test; !"\nNo", "token", "stack", "queue"
+
+Dim As Integer i = 0
+Do
+    i += 1
+    token = word_(test, i)
+    If token = "" Then Exit Do
+    Print i, token, reverse(stack), queue
+
+    Select Case token
+    Case "("
+        stackPush(token)
+
+    Case ")"
+        While stackPeek() <> "("
+            If stack = "" Then Print "Error: no matching '(' for token "; i: Sleep: End
+            queuePush(stackPop())
+        Wend
+        Dim As String discard = stackPop()   'discard "("
+
+    Case Else
+        If isOperator(token) Then
+            Dim As String op1 = token
+            While isOperator(stackPeek())
+                Dim As String op2 = stackPeek()
+                If op2 <> "^" And precedence(op1) = precedence(op2) Then
+                    queuePush(stackPop())
+                Else
+                    Exit While
+                End If
+            Wend
+            stackPush(op1)
+        Else   'number
+            queuePush(token)
+        End If
+    End Select
+Loop
+
+While stack <> ""
+    If stackPeek() = "(" Then Print "no matching ')'": Sleep:End
+    queuePush(stackPop())
+Wend
+
+Print !"\nOutput:"
+While queue <> ""
+    Print queuePop(); " ";
+Wend
+
+Sleep