gno.land/r/moul/x/daily/calc/v0⧉

1package calc23import (4	"chain"5	"errors"6	"strconv"7	"strings"8)910// stack holds the shared RPN operand stack, bottom (index 0) to top.11var stack []int1213// ErrUnderflow is raised when an operator needs more operands than available.14var ErrUnderflow = errors.New("stack underflow: operator needs two operands")1516// ErrDivByZero is raised on division by zero.17var ErrDivByZero = errors.New("division by zero")1819// Push consumes a single token: an integer is pushed onto the stack; an20// operator (+, -, *, /) pops two operands and pushes the result.21func Push(cur realm, token string) {22	token = strings.TrimSpace(token)23	if token == "" {24		panic("empty token")25	}2627	switch token {28	case "+", "-", "*", "/":29		if len(stack) < 2 {30			panic(ErrUnderflow.Error())31		}32		b := stack[len(stack)-1]33		a := stack[len(stack)-2]34		stack = stack[:len(stack)-2]3536		var r int37		switch token {38		case "+":39			r = a + b40		case "-":41			r = a - b42		case "*":43			r = a * b44		case "/":45			if b == 0 {46				panic(ErrDivByZero.Error())47			}48			r = a / b49		}50		stack = append(stack, r)51		chain.Emit("Op", "op", token, "result", strconv.Itoa(r))52	default:53		n, err := strconv.Atoi(token)54		if err != nil {55			panic("invalid token: expected integer or one of + - * /, got " + token)56		}57		stack = append(stack, n)58		chain.Emit("Push", "value", strconv.Itoa(n))59	}60}6162// Clear empties the shared stack.63func Clear(cur realm) {64	stack = nil65	chain.Emit("Clear")66}6768// Depth returns the number of values currently on the stack.69func Depth() int {70	return len(stack)71}7273// Top returns the top value and whether the stack is non-empty.74func Top() (int, bool) {75	if len(stack) == 0 {76		return 0, false77	}78	return stack[len(stack)-1], true79}8081// Render renders the current stack, the top value as the result, and a82// short usage guide.83func Render(path string) string {84	var sb strings.Builder85	sb.WriteString("# RPN Calculator\n\n")8687	sb.WriteString("## Result\n\n")88	if top, ok := Top(); ok {89		sb.WriteString("**")90		sb.WriteString(strconv.Itoa(top))91		sb.WriteString("**\n\n")92	} else {93		sb.WriteString("_(empty stack)_\n\n")94	}9596	sb.WriteString("## Stack (bottom → top)\n\n")97	if len(stack) == 0 {98		sb.WriteString("_empty_\n\n")99	} else {100		for i, v := range stack {101			sb.WriteString(strconv.Itoa(i))102			sb.WriteString(". ")103			sb.WriteString(strconv.Itoa(v))104			sb.WriteString("\n")105		}106		sb.WriteString("\n")107	}108109	sb.WriteString("## Usage\n\n")110	sb.WriteString("Reverse Polish Notation: operands first, operator last.\n\n")111	sb.WriteString("- `Push(\"5\")` then `Push(\"3\")` then `Push(\"+\")` → `8`\n")112	sb.WriteString("- Supported operators: `+`, `-`, `*`, `/` (integer division)\n")113	sb.WriteString("- An operator pops the top two values (a, b) and pushes `a op b`.\n")114	sb.WriteString("- `Clear()` empties the stack.\n")115	sb.WriteString("- Divide-by-zero and underflow abort the transaction.\n")116117	return sb.String()118}119