109 lines
1.8 KiB
Go
109 lines
1.8 KiB
Go
package rpn
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import (
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"errors"
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"math"
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)
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var ErrExit = errors.New("exit")
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type RPN struct {
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stack *Stack
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lexer *Lexer
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}
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func NewRPN() *RPN {
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return &RPN{
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stack: &Stack{},
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lexer: &Lexer{},
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}
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}
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func printHelp() {
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println("RPN Calculator")
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println("==============")
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println("Commands:")
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println(" +, -, *, /, %, ^, sqrt")
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println(" pop, swap")
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println(" help")
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println(" exit (or Ctrl-D)")
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println("Examples:")
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println(" 1 2 + == 3")
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println(" 2 3 4 + *")
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println(" 2 3 4 + * 5 /")
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println(" 9 sqrt")
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println(" 2 3 swap -")
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println(" exit")
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}
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func (r *RPN) Eval(input string) error {
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tokens, err := r.lexer.Parse(input)
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if err != nil {
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return err
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}
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for _, token := range tokens {
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switch token.Type {
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case number:
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r.stack.Push(token.Value)
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case binaryOp:
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a, b, err := r.stack.Pop2()
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if err != nil {
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return err
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}
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switch token.Operator {
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case plus:
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r.stack.Push(b + a)
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case minus:
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r.stack.Push(b - a)
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case multiply:
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r.stack.Push(b * a)
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case divide:
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if a == 0 {
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r.stack.Push(b)
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r.stack.Push(a)
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return errors.New("can't divide by zero")
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}
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r.stack.Push(b / a)
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case mod:
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r.stack.Push(float64(int64(b) % int64(a)))
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case power:
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r.stack.Push(math.Pow(b, a))
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}
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case unaryOp:
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a, err := r.stack.Pop()
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if err != nil {
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return err
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}
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switch token.Operator {
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case sqrt:
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r.stack.Push(math.Sqrt(a))
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}
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case pop:
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_, err := r.stack.Pop()
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if err != nil {
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return err
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}
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case swap:
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err := r.stack.Swap()
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if err != nil {
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return err
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}
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case clr:
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r.stack.Clear()
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case help:
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printHelp()
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case exit:
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return ErrExit
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default:
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return errors.New("Unknown operation")
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}
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}
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return nil
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}
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func (r *RPN) PrintStack() {
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r.stack.Print()
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}
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