[Haskell-cafe] accessible layout proposal?

Richard O'Keefe ok at cs.otago.ac.nz
Tue Sep 22 22:20:53 EDT 2009

On Sep 23, 2009, at 12:24 PM, James Hartzell wrote:

>> Well, look at code like this:
> wrapParens str = concat [
>   "(",
>   str,
>   ")"
>  ]

I just did.  I'd write it as

     wrap_parens s = "(" ++ s ++ ")"

although I wouldn't use that name, because it's not the
parentheses that are wrapped, it's s.

> First off, there is a serious issue with the commas.

> You should at least
> be allowed to have a comma after the last element, a la Python.

Oh, I agree about that.  I've written an Erlang Extension
Proposal for Erlang about that.

> concat [
>   "(",
>   str,
>   ")"     -- (oops, no comma!)
>   lineEnd -- forgot I needed this
> ]

     "(" ++ str ++ ")" ++ line_end

I'm actually quite serious here.  Using infix ++ we have
the SAME problem about missing ++ as we do about mssing ,
After all, someone might have started with
	  "(" ++
	  str ++
and ended up with
	  "(" ++
	  str ++
	  ")"     -- (oops, no ++!)
	  lineEnd -- forgot I needed this

I asked for the trailing comma in Erlang for _social_ reasons,
not because I believed it would fix all problems of this type.

> And as to the "simplifying your code" idea: however "pure" your code  
> is,
> you will regularly have to embed lists of things in it (ADTs, export
> lists, data from the domain). And unless you're claiming it is *almost
> always bad style to have code looking like (from the proposal):
> main = do
>              a <- getChar
>              bracket_
>                  (enter a)
>                  (exit a)
>                  (do
>                      putChar a
>                      putStrLn "hello")

The thing about toy examples is that they are toy size.
On an example this size, we don't NEED fancy new stuff.

Actually, I'd write

main =
     getChar >>= \a ->
     bracket_ (enter a) (exit a) (putChar a >> putStrLn "hello")

so even _with_ this proposal, I'd still need exactly the same
parentheses.  One thing I might do is this:

enter_exit_bracket a body =
     bracket_ (enter a) (exit a) body

and then

main =
     getChar >>= \a ->
     enter_exit_bracket a (putChar a >> putStrLn "hello")

because it looks very much as if enter and exit exist only
to be passed (with suitable parameters) to bracket_.
> But I would *still* rather have:
> with a = bracket_ $#
>    enter a
>    exit a
> Layout is easier to read than parentheses.

It all depends on size (small things being easy pretty much
no matter what you do) and tools (tools where you click just
inside parentheses and the bracketed thing lights up, like
the traditional Smalltalk interface make parentheses very very
easy to read).

> In summary, I have to spend a good portion of my time coding Haskell
> dealing with the fact that I have a lot of {'s, ['s, and ,'s to keep  
> track
> of, and they rarely fit on one line (records, ADTs, lists). I have to
> spend a significant amount of my coding time finagling the layout to  
> look
> sensible, and I don't think anyone would claim that I just shouldn't  
> use
> records or ADTs.

For what it's worth, the editor I normally use has an
"add new element to list" command.

Where I'm coming from is this:
   I do not find meaningless jumbles of special characters
   combined with overloaded white space readable.

It would be so much better if we could discuss a _real_

More information about the Haskell-Cafe mailing list