Hedgehog is a simple dynamic programming language made with yacc and lex.

There is a simple blog about the detail of the implementation in Chinese: 自制简易解释器.

• Value

  a = 10;//int
  b = 3.14;//float
  c = true;//boolean
  d = null;//null
  s = "Hello, World!";//string
  

• Control

  There must be {} after if, elsif and else, even if there is only one statement in the block.

  a = 10;
  if a > 10 { // `()` is not necessary.
      b = a+20;
  } elsif a==10 {
      b = a+10;
  } else {
      b = a-10;
  }
  print(b);
  // block has no local environment, 
  // so 'b' is a global variable.
  

• Loops

  There is no while loop, for for can replace it.

  for i=0; i<10; i=i+1 {
      print(i);
      if i>=4 {break;}
  }
  i = 0;
  for i<10 {
      if i<5 {continue;}
      print(i);
  }
  

• Function

  A function is also treated as a value.

  func Hello() {
      print("Hello, world!");
  }
  
  Hello();
  

  func fbi(n) {
      a, b = 0, 1;
      for a<n {
          print(a);
          a, b = b, a+b;
      }
  }
  
  fbi(100);
  

  func factorial(n) {
      if n==0 {return 1;}
      return n*factorial(n-1);
  }
  
  print(factorial(5));
  

  And there is only one native function so far, print, which takes one value argument.

• Operator

  Most operator in hedgehog is the same with c. However, there is only one & for logical and, and one | for logical or.

  b = 2;
  a = 10;
  if a>20 & b<10 {
      print("`b` is less than 10 and `a` is greater than 20");
  }
  if a>20 | b<10 {
      print("`b` is less than 10 or `a` is greater than 20");
  }
  

yacc -d hedgehog.y
lex hedgehog.l
gcc -std=c99 -o hedgehog *.c

run test:

./hedgehog test/tes.hg

code examples:

print("Hello world");

func fibonacci(n) {
    if n < 0 {
        return -1;
    } elsif n == 0 {
        return 0;
    } else {
        a, b = 0, 1;
        for j=1;j<n;j=j+1 {
            a, b = b, a+b;
        }
        return b;
    }
}

print(fibonacci(20));

func fibonacci(n) {
    if n<0 {return -1;}
    elsif n==0 {return 0;}
    elsif n==1 {return 1;}
    return fibonacci(n-1)+fibonacci(n-2);
}

print(fibonacci(20));