Jlox

Lox interpreter written in Java following the book Crafting Interpreters.

Branches:

• main

If you are in the main branch you are looking at the implementation derived from the book.
It has some solved challenges and my own modifications.

Changes:

• const - declaration for immutable data. Examples:
  

  // Values
  const x = 1;
  x = 2; // Error at 'x': Cannot reassign a constant.
  
  // Classes
  class A {
      init(b) { this.b = 1; }
  }
  
  const a = A(1);
  a.b = 2; // Error at 'b': Cannot modify a field of a constant object.
  
  // But this is allowed:
  var a_mut = a;
  a.b = 2; // No error
  

• break - statement for breaking out of loops. Example:

  for (var i = 0; i < 10; i = i + 1) {
      if (i == 5) break;
      print i;
  }
  
  Output:
  // 0
  // 1
  // 2
  // 3
  // 4
  

• continue - statement for skipping the rest of the loop body. Example:

  for (var i = 0; i < 10; i = i + 1) {
      if (i % 2 == 0) continue;
      print i;
  }
  
  Output:
  // 1
  // 3
  // 5
  // 7
  // 9
  

• Escape sequences in strings - [ \n, \r, \t, \b, \', \", \\ ]. Note " ' " still works, no need for " \' ". Examples:

  // New line
  print "Hello\nWorld"; // Hello
                        // World
                        // 
  
  // Tab
  print "Hello\tWorld"; // World  World
  
  // Backspace
  print "Hello\b World"; // Hell World
  

• String and number concatenation using the '+' operator.

  // string + number
  print "123" + 4; // 1234 (string)
  
  // number + string
  print 4 + "123"; // 4123 (string)
  

• def keyword before method declaration is now required.

  // Before
  class A {
      init() { print "A"; }
  }
  
  // Now
  class A {
      def init() { print "A"; }
  }
  

• lambda expressions - anonymous functions. Examples:

  // Single line
  const add = lambda(a, b) { return a + b; };
  print add(1, 2); // 3
  
  // Multi line
  const add = lambda(a, b) {
      var c = a + b;
      return c;
  };
  print add(3, 2); // 3
  

• imports - importing other files. Examples:

  // file1.lox
  import "file2";  // Hello from file2
  import "file3" as math;    
  
  fun foo() {
      print "Hello from foo of file1";
  }
  
  foo();  // Hello from foo of file1
  file2.foo();  // Hello from foo of file2
  
  print math.pow(2, -math.PI);  // 0.0625
  
  // file2.lox
  fun foo() {
      print "Hello from foo of file2";
  }
  
  print "Hello from file2";
  
  // file3.lox
  fun pow(val, exp) {
      if (exp < 0) {
          return 1 / pow(val, -exp);
      }
      var result = 1;
      for (var i = 0; i < exp; i = i + 1) {
          result = result * val;
      }
      return result;
  }
  
  const PI = 3.14;
  

• modulo operator. Examples:

  print 4 % 2; // 0
  print 5 % 2; // 1
  

• jlox

If you are in the jlox branch you are looking at the implementation following the book.