started work on porting it to golang

go/calc.go

@@ -0,0 +1,155 @@
+package main
+
+import (
+	"fmt"
+	"regexp"
+	"strconv"
+	"strings"
+
+	"github.com/chzyer/readline"
+)
+
+type Calc struct {
+	debug     bool
+	batch     bool
+	stdin     bool
+	stack     *Stack
+	completer readline.AutoCompleter
+}
+
+const Help string = `Available commands:
+batch   enable batch mode
+debug   enable debug output
+dump    display the stack contents
+clear   clear the whole stack
+shift   remove the last element of the stack
+help    show this message
+
+Available operators:
+basic operators: + - * /
+`
+
+func NewCalc() *Calc {
+	c := Calc{stack: NewStack(), debug: false}
+
+	c.completer = readline.NewPrefixCompleter(
+		readline.PcItem("dump"),
+		readline.PcItem("debug"),
+		readline.PcItem("clear"),
+		readline.PcItem("batch"),
+		readline.PcItem("shift"),
+		readline.PcItem("undo"),
+		readline.PcItem("help"),
+		readline.PcItem("+"),
+		readline.PcItem("-"),
+		readline.PcItem("*"),
+		readline.PcItem("/"),
+	)
+
+	return &c
+}
+
+func (c *Calc) ToggleDebug() {
+	c.debug = !c.debug
+	c.stack.ToggleDebug()
+}
+
+func (c *Calc) ToggleBatch() {
+	c.batch = !c.batch
+}
+
+func (c *Calc) ToggleStdin() {
+	c.stdin = !c.stdin
+}
+
+func (c *Calc) Eval(line string) {
+	line = strings.TrimSpace(line)
+	space := regexp.MustCompile(`\s+`)
+	simple := regexp.MustCompile(`[\+\-\*\/]`)
+
+	if line == "" {
+		return
+	}
+
+	for _, item := range space.Split(line, -1) {
+		num, err := strconv.ParseFloat(item, 64)
+
+		if err == nil {
+			c.stack.Backup()
+			c.stack.Push(num)
+		} else {
+			if simple.MatchString(line) {
+				c.simple(item[0])
+				continue
+			}
+
+			switch item {
+			case "help":
+				fmt.Println(Help)
+			case "dump":
+				c.stack.Dump()
+			case "debug":
+				c.ToggleDebug()
+			case "batch":
+				c.ToggleBatch()
+			case "clear":
+				c.stack.Backup()
+				c.stack.Clear()
+			case "shift":
+				c.stack.Backup()
+				c.stack.Shift()
+			case "undo":
+				c.stack.Restore()
+			default:
+				fmt.Println("unknown command or operator!")
+			}
+		}
+	}
+}
+
+func (c *Calc) Result() {
+	if !c.stdin {
+		fmt.Print("= ")
+	}
+
+	fmt.Println(c.stack.Last())
+}
+
+func (c *Calc) simple(op byte) {
+	c.stack.Backup()
+
+	for c.stack.Len() > 1 {
+		b := c.stack.Pop()
+		a := c.stack.Pop()
+		var x float64
+
+		if c.debug {
+			fmt.Printf("DEBUG:        evaluating: %.2f %c %.2f\n", a, op, b)
+		}
+
+		switch op {
+		case '+':
+			x = a + b
+		case '-':
+			x = a - b
+		case '*':
+			x = a * b
+		case '/':
+			if b == 0 {
+				fmt.Println("error: division by null!")
+				return
+			}
+			x = a / b
+		default:
+			panic("invalid operator!")
+		}
+
+		c.stack.Push(x)
+
+		if !c.batch {
+			break
+		}
+	}
+
+	c.Result()
+}