Graal Forums - Functions as parameters

Have you ever wondered if you could pass functions as parameters, and how that could help you sometimes? Well, I tried I guess.

What could you use functions as parameters for? You could pass on execution logic for said function when a certain thing happens in the logic above it. (functions like map,filter,find,each from other languages, or sorting algorithms)

Lets see.. first, lets make an example:

You have an array of numbers from 1 to 9. Your task is to create a function which doubles all array values. Preferably passing the doubling rule as a function to the array iterator.

PHP Code:


		
			
function onCreated() {
  temp.array = {
    1, 2, 3,
    4, 5, 6,
    7, 8, 9
  };

  this.double = function (x) {
    return x*2;
  };

  this.filter = function (array, f) {
    temp.r = {};
    for(temp.i:array) {
      temp.check = f(temp.i);
      if(temp.check) temp.r.add(temp.check);
    }
    return temp.r;
  };

  temp.test = this.filter(temp.array, this.double);
  echo(temp.test);
  // above won't work, gives:
  // Script: Function f not found 

  temp.test = this.filter(temp.array, function(x) {
    return x*2;
  });
  // the above will actually give you a lot of errors like
  // unexpected token, missing semicolon etc
}

You'll notice at first, Graal doesn't really fully support anonymous functions or passing on functions assigned to a variable. So how does one do it in Graal? Oddly enough, there's a weird workaround:

PHP Code:


		
			
function onCreated() {
  this.filter = function (array, f) {
    temp.r = {};
    for(temp.i:array) {
      temp.check = f(temp.i);
      if(temp.check) temp.r.add(temp.check);
    }
    return temp.r;
  };

  temp.array = {
    1, 2, 3,
    4, 5, 6,
    7, 8, 9
  };

  temp.test = this.filter(temp.array, this.f = function(x) {
    return x*2;
  });
  echo(temp.test);
  // 2,4,6,8,10,12,14,16,18

  // you can actually even do this:

  this.double = function (x) {
    return x*2;
  };

  temp.test = this.filter(temp.array, this.f = this.double);
  echo(temp.test);
  // 2,4,6,8,10,12,14,16,18
}

Do you see it yet? There's a meaning behind using this.f at these instances:

temp.test = this.filter(temp.array, this.f = function(x) {
return x*2;
});

temp.test = this.filter(temp.array, this.f = this.double);

Wait, no, this is actually just a mayor workaround

PHP Code:


		
			
function onCreated() {
  this.each = function (list, f) {
    for(temp.i=0;i<list.size();i++) f(list[i],i,list);
  };
  // md5 each element and salt with iterator count,
  // and print 6 first letters
  this.each(temp.array, this.f = function(e,i,array) {
    temp.str = md5(e+i);
    echo(temp.str.substring(0,6));
  });
  // works printing:
  // 6bb61e
  // cfcd20
}

If ones does ONE change:

PHP Code:


		
			
function onCreated() {
  this.each = function (list, ff) {
    for(temp.i=0;i<list.size();i++) ff(list[i],i,list);
  };
  // md5 each element and salt with iterator count,
  // and print 6 first letters
  this.each(temp.array, this.f = function(e,i,array) {
    temp.str = md5(e+i);
    echo(temp.str.substring(0,6));
  });
  // works printing:
  // Script: Function ff not found 
}

The only way for this to work, is if you name all your function parameters as f and only use f when accessing said function parameters inside the function logic, naming must be consistent for it to be of any use, and current state makes it a hazzle.

All it does is actually setting this.f to the function in the running script, making it "kinda global" in that script. This in returns allows use of this.f and/or f inside the functions as well, as they all inherit this, and they point to the variable this.f which was set during calling of the function. All an illusion kind of.

I wish Graal had support for proper anonymous functions. (PS: I used filter deliberately)