class ProgramNode(
        val procedures: ArrayList<ProcedureNode>
)

class ProcedureNode(
        val statementListNode: StatementListNode
)

class StatementListNode(
        val statementList: ArrayList<StatementNode>
)

open class StatementNode

class AssignNode(
        val variable: VariableNode,
        val expr: ExpressionNode
) : StatementNode()

class CallNode(
        val procedure: ProcedureNode
) : StatementNode()

class WhileNode(
        val variable: VariableNode,
        val statementList: StatementListNode
) : StatementNode()

class IfNode(
        val variable: VariableNode,
        val thenStatementList: StatementListNode,
        val elseStatementList: StatementListNode
) : StatementNode()

open class ValueNode

class VariableNode(
        val name: String,
        val value: ExpressionNode = RefExpression(ConstantNode(0))
) : ValueNode()

class ConstantNode(
        val value: Int
) : ValueNode()

abstract class ExpressionNode {
    abstract fun evaluate() : Int
}

class PlusExpression(
        val expr0: ExpressionNode,
        val expr1: ExpressionNode
) : ExpressionNode() {
    override fun evaluate(): Int {
        return expr0.evaluate() + expr1.evaluate()
    }
}

class MinusExpression(
        val expr0: ExpressionNode,
        val expr1: ExpressionNode
) : ExpressionNode() {
    override fun evaluate(): Int {
        return expr0.evaluate() + expr1.evaluate()
    }
}

class TimesExpression(
        val expr0: ExpressionNode,
        val expr1: ExpressionNode
) : ExpressionNode() {
    override fun evaluate(): Int {
        return expr0.evaluate() + expr1.evaluate()
    }
}

class RefExpression(
        val ref: ValueNode
) : ExpressionNode() {
    override fun evaluate(): Int {
        when (ref) {
            is VariableNode -> return ref.value.evaluate()
            is ConstantNode -> return ref.value
        }
        throw IllegalStateException("Ref expression tried to fetch value of something that is neither Variable or ConstantNode")
    }
}