Re: [Haskell-cafe] indentation with let and do

3 Oct 2013

      On Thu, Oct 3, 2013 at 9:44 PM, Brandon Allbery  wrote:
...
On Thu, Oct 3, 2013 at 2:31 PM, Corentin Dupont 
...
wrote:
...
test :: Bool -> IO ()
test foo = do
   let bar = case foo of
       True ->  "Foo";
       False -> "Bar"
   return ()
while this one does (just adding one space in front of True and False):
test :: Bool -> IO ()
test foo = do
   let bar = case foo of
        True ->  "Foo";
        False -> "Bar"
   return ()
Do you understand how layout works? Informally, something that is more
indented is a continuation of the previous expression, while something
equally or less indented is a new expression. In this case, the previous
expression is `bar = case foo of` and indenting `True` to the same level as
`bar` means you have ended the expression starting with `bar =`. Adding
just one extra space indicates that it's still part of `bar =`.
(ghc is actually being somewhat lenient here; strictly speaking, you are
not indented beyond the `case` so it should have ended the `case`
expression. ghc allows some sloppiness like this when there absolutely must
be something else after, but there are limits mostly imposed by layout
introducers like `let` and `do`.)
Brandon,

Indentation of 'case' itself doesn't matter. The layout is introduced by
'of', and then it's the indentation of the lexeme which follows 'of' that
matters. So GHC is correct here.

Roman

Re: [Haskell-cafe] indentation with let and do

Roman Cheplyaka