[Haskell-cafe] Bad "let..do" syntax

[David House]

On 17/05/07, Chad Scherrer <chad.scherrer at gmail.com> wrote:
> But GHC complains of "Empty 'do' construct".

Because it takes the indented following lines as being new bindings in
the let-block. The trick is to intent them past the 'sum':

let b = sum $ do
          y <- [0..x + 1]
          return y

Or to bypass layout altogether:

let { b = sum $ do
  y <- [0..x + 1]
  return y }

(Of course, in this specific case I'd write sum [0..x + 1], but I
guess that this is an example of a general case.)

-- 
-David House, dmhouse at gmail.com