I just posted a new version of ocaml+twt, a preprocessor that lets you use indentation to avoid multi-line parenthesization (like Python or Haskell).

 

http://people.csail.mit.edu/mikelin/ocaml+twt

This version introduces a major backwards-incompatible change: the eradication of "in" from let expressions, and the need to indent the let body (as suggested by the F# lightweight syntax). This reduces the familiar phenomenon of long function bodies getting progressively more indented as they go along. That is, before where you had:

 

let x = 5 in

  printf "%d\n" x

  let y = x+1 in

    printf  "%d\n" y

 

You'd now just write:

 

let x = 5

printf "%d\n" x

let y = x+1

printf "%d\n" y

I was hesitant to introduce this feature because it's extra hackish in implementation (even moreso than the rest of this house of cards). It also removes some programmer freedom, because you cannot have the let body on the same line as the let, and you cannot have a statement sequentially following the let, outside the scope of the binding. But after playing with it, I think it is worthwhile. Please let me know what you think. I am still not completely sure that I haven't broken something profound that will force me to totally backtrack this change, but let's give it a try. I will obviously keep the  0.8x versions around for those who prefer it and for existing code (including a lot of my own).

 

Standard disclaimer: ocaml+twt is a flagrant, stupendous, borderline-ridiculous hack, but it works quite well, I write all my new code using it, and I recommend it if you like this style. On the other hand, if someone with more free time and knowledge of camlp4 wants to step up, I have a couple ideas about how you might do it right...

Mike