Re: How to improve the readability of (any) LISP or any highlevel functional language to the level of FORTH ?

[Paul Rubin]

LanX <lanx.perl@googlemail.com> writes:
>>    main = print [head xs | xs <- group my_list]
>
> does this really produce the desired output?
> Will the second 1 really be printed?

Yes.  "group" is a very useful function, that transforms a list into a
list-of-lists which collapses identical elements:

    group [1, 1, 1, 1, 2, 3, 3, 1, 1, 4, 5, 5, 5, 5]

is

    [[1,1,1,1], [2], [3,3], [1,1], [4], [5,5,5,5]]

The list comprehension 

     [head xs | xs <- group my_list]

simply collects the first element of each of those sub-lists.

There is also groupBy, which lets you supply your own equality
predicate.  If there's not already a Lisp library similar to Python's
itertools module and Haskell's List module, it's probably worth writing
one.