Bad "let..do" syntax

17 May 2007

      I've gotten into a habit of preceding most "do"s in my code with a
"$", and indenting the next line. I kind of like this, since it makes
the indentation more uniform. But it seems to have bitten me now. I'd
like to write something like this

s = sum $ do
  x <- [1,2,3]
  let b = sum $ do
    y <- [0..x + 1]
    return y
  return (x + b)

But GHC complains of "Empty 'do' construct". It likes the alternative

s' = sum $ do
  x <- [1,2,3]
  let b = sum $ do y <- [0..x + 1]
                   return y
  return (x + b)

just fine, but that looks horrible to me (ok, "horrible" is a bit
strong, but I don't like it as much).

So I'm wondering, (1) Is this intended to give an error, or is it just
a momentary hiccup, and (2) if others have run into this, is there a
more aesthetic alternative that works?

Thanks,

Chad

Chad Scherrer

David House

Chad Scherrer

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