kotlinlox/src/main/fr/celticinfo/loxext/RpnPrinter.kt

package fr.celticinfo.loxext

import fr.celticinfo.lox.*

class RpnPrinter : ExprVisitor<String> {
    fun print(expr: Expr): String {
        return expr.accept(this)
    }

    override fun visitBinary(binary: Binary): String {
        return stack(binary.operator.lexeme, binary.left, binary.right)
    }

    override fun visitGrouping(grouping: Grouping): String {
        return stack("", grouping.expression)
    }

    override fun visitLiteral(literal: Literal): String {
        return literal.value?.toString() ?: "nil"
    }

    override fun visitUnary(unary: Unary): String {
        return stack(unary.operator.lexeme, unary.right)
    }

    private fun stack(name: String, vararg exprs: Expr): String {
        val builder = StringBuilder()
        for (expr in exprs) {
            builder.append(expr.accept(this))
            if (name.isNotEmpty()) builder.append(" ")
        }
        builder.append(name)
        return builder.toString()
    }
}