LESS is More

When a programer looks at a new language which is slightly different than general programming languages, first question that comes to his mind is if the language is turing complete. Similar thing happened to me when I looked at LESS. LESS is a CSS preprocessor and from a cursory look it looks like a macro sort of language which copy pastes definitions from one place to another. Actually, it is little more than that as it also tries to be a CSS like declarative language. That is, instead of defining variable you define properties and order defining those properties does not matter. Nevertheless, I have still not well understood the model of computation followed by this language, but it seems that even implementing a counter in this language is not very straightforward. I do not have anything to say to creators of LESS as it is not intended to be a general purpose language. Language does allow mathematical expression, variable definition, conditions (guards), methods. With these tools at hand I thought it would be easy to implement loops using recursion and calculate factorial and fibonacci sequence. My first attempt at creating a program that will find the factorial of a given number failed as it seems language does not allow updating a variable in a given scope once it is defined. At this point I knew that probably language does not well support writing such routines. I googled a lot to see if someone else has done something like this, but did not find anything. I was now looking for a language feature which could be exploited to carry out calculations and also preserve state. After trying many things I found that if you keep all the state in the form of parameters of a function (mixin), it is possible to get the effect of modifying a variable (state updation). Below are some programs I wrote for calculating factorial and fibonacci numbers

  
.fact_impl(@n,@res) when (@n > 1){
   .fact_impl(@n - 1, @res * (@n - 1));
}

.fact_impl(1,@res){
  @fact_res:@res;
}
.fact(@k){
  .fact_impl(@k,@k);
}

.fib_impl(@n,@first,@second) when (@n > 0){
  .fib_impl(@n - 1,@second,@first+@second);
}
.fib_impl(0,@first,@second){
  @fib_res:@first;
}
.fib(@k){
  .fib_impl(@k,0,1);
}

result{
  .fact(6);
  .fib(8);
  factorial_of_6:@fact_res;
  fibonacci_8:@fib_res;
}