Re: Comments on the preprocessor list data structure

From: vesa_karvonen (vesa_karvonen_at_[hidden])
Date: 2002-01-21 13:22:01

--- In boost_at_y..., Douglas Gregor <gregod_at_c...> wrote:
> On Monday 21 January 2002 06:53 am, you wrote:
> > //! Drops the first N elements of the list.
[...]
> > #define BOOST_PP_LIST_DROP(N,L)

> "Drop" doesn't really tell us anything about what's being dropped. 
How about 
> using REMOVE_FIRST instead, e.g.,
> 
> BOOST_PP_REMOVE_FIRST(2,BOOST_PP_TUPLE_TO_LIST(4,(+,-,*,/)))
> 
> Or, perhaps, to save typing, use REMOVE1ST.

The name "drop" is used for the same function in Haskell (and in 
several other more or less functional languages). I agree that it may 
sound a bit odd at first. The functions "drop" and "take" form a 
logical couple.

What do you think about the name "take"?

I think that 'remove_first' certainly sounds more like STL, 
but "drop" and "take" don't seem to have close enough relatives in 
STL, so that the names could just be borrowed.

I think that "remove_first" sounds like it would work like "tail" 
or "head" (depending on which part, "head" or "tail", is returned).

So, I like "drop" better than "remove_first". It is shorter, and I 
don't find it difficult to make the leap from "drop" to "drop the 
first N elements of a list".

> Otherwise, the naming is good

So, you like "fold_left" and "fold_right"?

I considered using "accumulate" (and "reverse_accumulate" 
and "accumulate_left", etc...), but IMO it sounds way too arithmetic. 
Also "fold" is well known concept in functional programming. 
Furthermore I don't want to make it appear as if either one of the 
folds would be more primitive.

> and the new facilities are very cool.

Thanks! :)

But you should really congratulate the people who invented functional 
programming. The preprocessor list data structure is just a rather 
straightforward implementation of functional lists.