Initial

1 files changed, 84 insertions, 0 deletions

diff --git a/example/math_expression/rpn.go b/example/math_expression/rpn.go
new file mode 100644
index 0000000..b65983d
--- /dev/null
+++ b/example/math_expression/rpn.go
@@ -0,0 +1,84 @@
+package main
+
+// Helper functions to convert infix notation to RPN and calculates expression result.
+
+import (
+	"fmt"
+	"log"
+	"strconv"
+
+	"github.com/neonxp/unilex"
+)
+
+func infixToRPNotation(l *unilex.Lexer) []unilex.Lexem {
+	output := []unilex.Lexem{}
+	stack := lexemStack{}
+parseLoop:
+	for ll := range l.Output { // Read lexems from Lexer output channel, convert starts as soon as first lexems scanned!
+		fmt.Printf("Lexem: %+v\n", ll)
+
+		switch {
+		case ll.Type == "NUMBER", ll.Type == "OPERATOR" && ll.Value == "!":
+			output = append(output, ll)
+		case ll.Type == "LP":
+			stack.Push(ll)
+		case ll.Type == "RP":
+			for {
+				cl := stack.Pop()
+				if cl.Type == "LP" {
+					break
+				}
+				if cl.Type == unilex.LEOF {
+					log.Fatalf("No pair for parenthesis at %d", ll.Start)
+				}
+				output = append(output, cl)
+			}
+		case ll.Type == "OPERATOR":
+			for {
+				if stack.Head().Type == "OPERATOR" && (opPriority[stack.Head().Value] > opPriority[ll.Value]) {
+					output = append(output, stack.Pop())
+					continue
+				}
+				break
+			}
+			stack.Push(ll)
+		case ll.Type == unilex.LEOF:
+			break parseLoop
+		}
+	}
+
+	for stack.Head().Type != unilex.LEOF {
+		output = append(output, stack.Pop())
+	}
+
+	return output
+}
+
+func calculateRPN(rpnLexems []unilex.Lexem) string {
+	stack := lexemStack{}
+	for _, op := range rpnLexems {
+		if op.Type == "NUMBER" {
+			stack.Push(op)
+		} else {
+			switch op.Value {
+			case "+":
+				a1, _ := strconv.ParseFloat(stack.Pop().Value, 64)
+				a2, _ := strconv.ParseFloat(stack.Pop().Value, 64)
+				stack.Push(unilex.Lexem{Type: "NUMBER", Value: strconv.FormatFloat(a2+a1, 'f', -1, 64)})
+			case "-":
+				a1, _ := strconv.ParseFloat(stack.Pop().Value, 64)
+				a2, _ := strconv.ParseFloat(stack.Pop().Value, 64)
+				stack.Push(unilex.Lexem{Type: "NUMBER", Value: strconv.FormatFloat(a2-a1, 'f', -1, 64)})
+			case "*":
+				a1, _ := strconv.ParseFloat(stack.Pop().Value, 64)
+				a2, _ := strconv.ParseFloat(stack.Pop().Value, 64)
+				stack.Push(unilex.Lexem{Type: "NUMBER", Value: strconv.FormatFloat(a2*a1, 'f', -1, 64)})
+			case "/":
+				a1, _ := strconv.ParseFloat(stack.Pop().Value, 64)
+				a2, _ := strconv.ParseFloat(stack.Pop().Value, 64)
+				stack.Push(unilex.Lexem{Type: "NUMBER", Value: strconv.FormatFloat(a2/a1, 'f', -1, 64)})
+			}
+		}
+	}
+	return stack.Head().Value
+}