recursive_call_explanation

def and_function(expression1, expression2):
    if expression1=="true" and expression2=="true":
        return "true"
    else:
        return "false"


def or_function(expression1, expression2):
    if expression1== "true" or expression2=="true":
        return "true"
    else:
        return "false"


def not_function(expression):
    if expression == "true":
        return "false"
    elif expression == "false":
        return "true"


binary_bool_dict = {'AND':and_function, 'OR':or_function}
unary_bool_dict = {'NOT':not_function}

def interpret( exprsn, dct):

    if isinstance( exprsn, list):
        lst = exprsn
        temp_result = None

        for idx, item in enumerate( lst):

            if item == 'true' or item == 'false':
                # item is already in its interpreted state
                continue

            elif isinstance( item, list):
                # recursive call cond 2)
                lst[idx] = interpret( item,dct)

            elif item in dct:
                # get the meaning of this item from dictionary
                lst[idx] = dct[item]

            else:
                # recursive call cond 1)
                lst[idx+1] = interpret( lst[ idx+1],dct)

                '''
                interpret(["NOT", ["lights_on", "AND" , "candleNeeded"]],{"lights_on":"true", "candleNeeded" :"false"})
                temp_result = None

                item --> "NOT" ie item is in unary_bool_dict

                NOT requires operand on right side to be interpreted completely first ( we can do short-circuit-eval for OR, AND see the improved version of answer)

                next item( right operand) is a list so we will make a recursive call( cond 2)

                { lst[idx+1] }{1} = interpret( { lst[ idx+1] }{2}, {dct}{3} ) after finding interpretation of list we will replace with its interpretation

                ["lights_on", "AND" , "candleNeeded"]{1} = interpret( ["lights_on", "AND" , "candleNeeded"]{2},{lights_on:"true", candleNeeded: "false"}{3} )

                lst[idx+1] = "false"

                now our orignal list arguement has become = ["NOT","false"]

                temp_result = unary_bool_dict[item]("false")

                temp_result = "true"

                '''

                if item in binary_bool_dict:

                    if temp_result == None:
                        temp_result = binary_bool_dict[item]( lst[ idx-1], lst[idx+1])
                    else:
                        temp_result = binary_bool_dict[item]( temp_result, lst[idx+1])

                else:
                    # item in unary_bool_dict:
                    temp_result  = unary_bool_dict[item](lst[idx+1])

        return temp_result # eventually temp_result will become our final answer

    else:
        return dct.get( exprsn,exprsn) # if exprsn( as key) is present in dct get its value else just return exprsn ( it must be already a 'true' or 'false')


print(interpret(["NOT", ["lights_on", "AND" , "candleNeeded"]],{"lights_on":"true", "candleNeeded" :"false"}))