Supporting Handlebars subexpressions

I saw this question Handlebars subexpression throws “options.fn is not a function” error on stackoverflow:

The OP was asking why {{#and (gt 4 3) (gt 5 4)}}OK{{/and}} will throw a:

TypeError: options.fn is not a function

In the code it is obvious the helper requires fn and inverse (so an if/else) block:

helpers.gt = function(a, b, options) {
  if (arguments.length === 2) {
    options = b;
    b = options.hash.compare;
  }
  if (a > b) {
    return options.fn(this);
  }
  return options.inverse(this);
};

To support {{#and (gt 4 3) (gt 5 4)}}OK{{/and}} the helper should return true or false instead of options.fn(this) or options.inverse(this) if those blocks don’t exists.

This might probably be a interesting feature. Or am I missing something here?

To support subexpressions the code could be changed to this:

helpers.gt = function(a, b, options) {
  if (arguments.length === 2) {
    options = b;
    b = options.hash.compare;
  }

  //fn block exists: it is not a subexpression
  if( options.fn ) {
     if (a > b) {
       return options.fn(this);
     }
     return options.inverse(this);
  } else { // otherwise return the result of the comparison
     return a > b;
  }
};

[tndev]

If you convert it to assert anyway, then I’ll use assert. I just looked around in your tests where you compare to 'true' in a non block helper and adapted that style.

[jonschlinkert]

@tndev great, I was thinking about this, I like the concept but it would help to see the code so we can discuss. Feel free to do the pr, thx