Question

USE SCALA ONLY:

Here is an example of “Our Language”

1. integer a

2. integer b

3. string name

4. a = 14

5. b = 27

6. c = a + b

7. name = “example program”

8. display name

9. display c

10. read a

11. b = a * a

12. display a

13. end

Your interpreter will:

(a) Create an empty Map[String, String]

(b) Read the program

(c) Print each line as it is read

(d) Store each line into a text file

(e) Whenever a variable is declared (lines 1, 2 and 3, above), the variable name will be used to create a key -> value pair (variable name as the key and variable value as the value of the pair, converted to a string if necessary, and added to the Map)

(f) If an error is detected while reading the program text (lines 6 and 9, above, where c is an undeclared variable), a message will be printed along with the line of code

(g) When the “end” is reached, if any error has been detected during the reading, a message will be printed, saying that the program cannot be executed.

(h) If no error has been detected, your interpreter will begin to execute the program by reading it, line by line from the text file where you stored it and performing each line.

(i) Lines 1, 2 and 3 will cause entries to be created and added to the Map Lines 4 and 5 will cause the values 14 and 27 to be stored in the Map as the value part of the key -> value pair that has the variable name as the key Line 6 (if the name c had not been an undeclared variable) would cause the interpreter to look up the names a and b in the map and use their current values to be added and the result stored as the value for the pair whose key is c

The lines with "Display" (lines 8, 9 and 12) will cause the displayed value to be printed to the user.

The lines with "Read”(line 10) will prompt the user to input a value which will then be stored in the Map

The result will be that your interpreter will have read your “program”, tested and saved it in a text file and recovered it from the text file, a line at a time and each line will be executed by the interpreter.

Please read the example and post an answer for this question. Again please write the code using scala only. Thanks

Answer 1

//save the following in filename.scala

import scala.io.Source
object HelloWorld {
  def main(args: Array[String]) {
    var error_count=0
    var line_number=0
    var int_variables_and_values:Map[String,Int] = Map()
    var string_variables_and_values:Map[String,String] = Map()
    val filename = "C:\\Users\\MANIKANTA\\IdeaProjects\\Chegg_scala\\src\\instructions.txt"
    for (line <- Source.fromFile(filename).getLines) {
      line_number+=1
      //comment the following line for clean expected outut
      println("Processing line "+line_number+" "+line)
      if(line!="end"){
        val string_array=line.split(' ')

        //declaring a int variable
        if(string_array(0)=="integer")
          int_variables_and_values+=(string_array(1)->0)

        //declaring a string variable
        else if(string_array(0)=="string")
          string_variables_and_values+=(string_array(1)->"")

        //to handle reading from console
        else if(string_array(0)=="read"){
            if(int_variables_and_values.contains(string_array(1))){
              print("Enter value for int "+ string_array(1)+": ")
              var input_int=scala.io.StdIn.readInt()
              int_variables_and_values+=(string_array(1)->input_int)
            }
            else if(string_variables_and_values.contains(string_array(1))){
              print("Enter value for string "+ string_array(1)+": ")
              var input_string=scala.io.StdIn.readLine()
              string_variables_and_values+=(string_array(1)->input_string)
            }
            else{
              error_count+=1
              println("ERROR :can not read for a un declared variable!")
            }
        }

        //to handle display
        else if(string_array(0)=="display"){
            if(int_variables_and_values.contains(string_array(1)))
              println(int_variables_and_values.get(string_array(1)).getOrElse(0))
            else if(string_variables_and_values.contains(string_array(1)))
              println(string_variables_and_values.get(string_array(1)).getOrElse(0))
            else {
              error_count+=1
              println("ERROR :can not diplay an un declared variable!")
            }
        }

        //to hanfle assgining
        else if(string_array(0).contains('=')){
          val assigining = line.split('=')
          //check int variables map for key exists or not
          if(int_variables_and_values.contains(assigining(0))){
            int_variables_and_values+=(assigining(0)->assigining(1).toInt)
          }
          //check string variables map for key exists or not
          else if(string_variables_and_values.contains(assigining(0))){
            string_variables_and_values+=(assigining(0)->assigining(1))
          }
          else{
            error_count+=1
            println("ERROR: undeclared variable "+assigining(0)+" encountered")
          }
        }
      }
      else if(line=="end" && error_count!=0) {
          println("As errors are present, program cannot be executed!")
          println(int_variables_and_values)
          println(string_variables_and_values)
      }
      else {
        println("Program Successfully executed")
        println(int_variables_and_values)
        println(string_variables_and_values)
      }
    }
  }
}