[Haskell-beginners] Re: mayBe stuck

[Dean Herington]

At 11:04 AM -0700 8/6/10, prad wrote:
>On Fri, 6 Aug 2010 03:43:30 -0400
>Dean Herington <heringtonlacey at mindspring.com> wrote:
>
>>  I would write something like:
>>
>>  br [] = []
>>  br ss = let (h, t) = break eqD ss
>>           in h : case t of
>>                    []    -> []
>>                    _ : t -> br t
>>
>thx dean. that certainly looks cleaner than mine, but i'm not sure i
>have seen this construct before.
>
>i thought let/in was used like this:
>
>aaa = let y = 1+2
>           z = 4+6
>           in  y+z
>
>which is like
>
>aaa = y + z
>     where y = 1+2
>           z = 4+6
>
>in other words, you just define the parts first and use the "in" to
>define the main expression.
>
>but here it seems you are defining what appears to be the main item
>let (h,t) = break eqD ss
>to get the tuple parts and then forming your array (which really is
>the main item) using these parts as
>h : t
>with t being given 2 options.
>
>this is very interesting to me as i had not seen such a construct
>before.

Choosing between `let` and `where` is usually a matter of taste.  I 
use both, depending on whether I think it's clearer to present the 
logic "bottom-up" or "top-down".  Here's the `where`-style equivalent 
of the `let` version:

br [] = []
br ss = h : case t of
               []    -> []
               _ : t' -> br t'
   where (h, t) = break eqD ss

For a reason I probably can't articulate well, I find the `let` 
version more readable in this case.  Perhaps it's because I 
understand the function as (1) `break`ing on '%', then (2) dealing 
with the details of recursing.

Cheers,
Dean