package typelang;
import java.io.IOException;
import typelang.Checker;
import typelang.Env;
import typelang.Type;
import typelang.Value;
import typelang.AST.*;
/**
* This main class implements the Read-Eval-Print-Loop of the interpreter with
* the help of Reader, Evaluator, and Printer classes.
*
* @author hridesh
*
*/
public class Interpreter {
public static void main(String[] args) {
System.out.println(“TypeLang: Type a program to evaluate and press the enter key,\n”
+ “e.g. ((lambda (x : num y : num z : num) (+ x (+ y z))) 1 2 3) \n” +
“or try (let ((x : num 2)) x) \n” +
“or try (car (list : num 1 2 8)) \n” +
“or try (ref : num 2) \n” +
“or try (let ((a : Ref num (ref : num 2))) (set! a (deref a))) \n” +
“Press Ctrl + C to exit.”);
Reader reader = new Reader();
Evaluator eval = new Evaluator(reader);
Printer printer = new Printer();
Checker checker = new Checker(); // Type checker
REPL: while (true) { // Read-Eval-Print-Loop (also known as REPL)
Program p = null;
try {
p = reader.read();
if(p._e == null) continue REPL;
Type t = checker.check(p); /*** Type checking the program ***/
if(t instanceof Type.ErrorT)
printer.print(t);
else {
try {
Value val = eval.valueOf(p);
printer.print(val);
} catch (Env.LookupException e) {
printer.print(e);
}
}
} catch (Env.LookupException e) {
printer.print(e);
} catch (IOException e) {
System.out.println(“Error reading input:” + e.getMessage());
} catch (NullPointerException e) {
System.out.println(“Error:” + e.getMessage());
}
}
}
}