Indentation of non-parallel list comprehensions is wrong.

[bremner]

forwarding http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=343248
Daniel Burrows writes:

haskell-mode indents parallel list comprehensions (the GHC extension)
just fine, but it seems to have trouble with non-parallel ones. For
instance, consider this code fragment:

allCards :: CardUniverse -> [CardValue]
allCards (CardUniverse s free) = free ++ suited
    where suited = [cv | suit <- s,
                         (cv, _) <- elems (suitCards suit)]

haskell-mode wants me to indent the last line to either the level of
"s" or the level of "cv" in the previous line; for instance:

-- | Returns a list of all the cards in the universe; this will be a
-- set if the universe is well-formed.
allCards :: CardUniverse -> [CardValue]
allCards (CardUniverse s free) = free ++ suited
    where suited = [cv | suit <- s,
                    (cv, _) <- elems (suitCards suit)]

I verified that this behaviour still exists with 2.8.0 and turn-on-haskell-indentation

[hvr]

btw, if you follow the leading-comma Haskell convention for list-like structures, e.g. as in

-- | Returns a list of all the cards in the universe; this will be a
-- set if the universe is well-formed.
allCards :: CardUniverse -> [CardValue]
allCards (CardUniverse s free) = free ++ suited
  where suited = [cv | suit <- s
                     , (cv, _) <- elems (suitCards suit)
                     ]

does it work as espected?

[bremner]

yes, that indentation looks reasonable to me in the leading-comma case.

[pheaver]

Ah, I have noticed this problem all the time, but just kept pushing it to the back of my mind. It would be nice to fix it.

[hvr]

@pheaver btw there's a related problem occurring even when using the leading-comma convention: when using let bindings within list comprehensions, at least one of the 3 indentation modes gets confused...

[chrisdone]

Gonna close in one month unless someone owns this.

[lukehoersten]

As Chris mentioned back in 2013, he was going to close this in a month. I confirmed hi2-mode still has this same behavior but the recommended indentation works correctly as this:

allCards :: CardUniverse -> [CardValue]
allCards (CardUniverse s free) = free ++ suited
  where suited = [ cv | suit <- s
                      , (cv, _) <- elems (suitCards suit)
                      ]