I wrote diffr [0] for that purpose; it serves me well, especially if your team makes code with long lines.
In my opinion, a simple approach that does NOT make any parsing is more efficient (what about bugs in your parser? code with syntax errors? also, how fast would the parser be?)
The point is to share intermediate state of your data structure without headache.
For instance, if you write an interpreter, representing variable bindings with a functional map allows to reason about scope super easily; when you change scope, you just create a new map with the new variable bindings, and when the scope ends you just get back the map at the scope beginning which is still valid.
With a stateful hashtable, you need to undo the changes you did in you scope; the value of the table when opening the scope that you want to get back to is gone forever. Now it ties you program to a certain execution order. One way to see that is that if you want to collect environment to each scope in some data structure for some reason, you need to make deep copies everywhere.
Unless experienced, you have no clue how a piece of code will be parsed. With ocaml, where is very little ambiguity; and indentation tools can take care of proper formatting, you only need to break lines.
And it can be pretty bad with haskell, which has complex semantics compared to, say, python.
With whitespace sensitive syntax, I feel like in the dark age of manual indentation.
To allow IEEE compliant float with tagged pointers.
However, note that floats are not boxed in the OCaml's arrays. Boxing floats is a pain because it makes the price of defining subroutines taking float arguments high.