[Haskell-beginners] Re: mayBe stuck

At 11:04 AM -0700 8/6/10, prad wrote:

On Fri, 6 Aug 2010 03:43:30 -0400 Dean Herington 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