Time for an 2014 update…

Task/Parsing-RPN-calculator-algorithm/Liberty-BASIC/parsing-rpn-calculator-algorithm.liberty

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+global stack$
+
+expr$ = "3 4 2 * 1 5 - 2 3 ^ ^ / +"
+print "Expression:"
+print expr$
+print
+
+print "Input","Operation","Stack after"
+
+stack$=""
+token$ = "#"
+i = 1
+token$ = word$(expr$, i)
+token2$ = " "+token$+" "
+
+do
+    print "Token ";i;": ";token$,
+    select case
+    'operation
+    case instr("+-*/^",token$)<>0
+        print "operate",
+        op2$=pop$()
+        op1$=pop$()
+        if op1$=""  then
+            print "Error: stack empty for ";i;"-th token: ";token$
+            end
+        end if
+
+        op1=val(op1$)
+        op2=val(op2$)
+
+        select case token$
+        case "+"
+            res = op1+op2
+        case "-"
+            res = op1-op2
+        case "*"
+            res = op1*op2
+        case "/"
+            res = op1/op2
+        case "^"
+            res = op1^op2
+        end select
+
+        call push str$(res)
+    'default:number
+    case else
+        print "push",
+        call push token$
+    end select
+    print "Stack: ";reverse$(stack$)
+    i = i+1
+    token$ = word$(expr$, i)
+    token2$ = " "+token$+" "
+loop until token$ =""
+
+res$=pop$()
+print
+print "Result:" ;res$
+extra$=pop$()
+if extra$<>"" then
+    print "Error: extra things on a stack: ";extra$
+end if
+end
+
+'---------------------------------------
+function reverse$(s$)
+    reverse$ = ""
+    token$="#"
+    while token$<>""
+        i=i+1
+        token$=word$(s$,i,"|")
+        reverse$ = token$;" ";reverse$
+    wend
+end function
+'---------------------------------------
+sub push s$
+    stack$=s$+"|"+stack$    'stack
+end sub
+
+function pop$()
+    'it does return empty on empty stack
+    pop$=word$(stack$,1,"|")
+    stack$=mid$(stack$,instr(stack$,"|")+1)
+end function