object SchemeInterpreter
val emptyEnvironment: Environment
val primitiveProcedures: HashMap[String, Procedure]

def add(operands: ListBuffer[Expression]): Expression
def sub(operands: ListBuffer[Expression]): Expression
def mult(operands: ListBuffer[Expression]): Expression
def div(operands: ListBuffer[Expression]): Expression
def abs(operands: ListBuffer[Expression]): Expression
def eq(operands: ListBuffer[Expression]): Expression
def less(operands: ListBuffer[Expression]): Expression
def great(operands: ListBuffer[Expression]): Expression
def cos(operands: ListBuffer[Expression]): Expression
def sin(operands: ListBuffer[Expression]): Expression
def tan(operands: ListBuffer[Expression]): Expression
def log(operands: ListBuffer[Expression]): Expression
def expt(operands: ListBuffer[Expression]): Expression

def define(exp: Node, env, Environment): Unit
def cond(exp: Node, env: Environment): Unit
def ifStatement(exp: Node, env: Environment): Unit

def isNumber(x: String): Boolean
def isBoolean(x: String): Boolean
def isString(x: String): Boolean
def toBoolean(x: String): Boolean
def getType(x: String): Expression
def lexer(input: String): Node
def makeTree(ls: ListBuffer[String], pointer: Int, adult: Node): Node
def printTree(current: Node): Unit

def selfEvaluating(x: Expression): Boolean
def valueList(exp: Node, ls: ListBuffer[Expression], env: Environment): ListBuffer[Expression]
def apply(proc: ListBuffer[Expression => Expression, args: ListBuffer[Expression]): Expression
def eval(exp: Node, env: Environment): Expression