Just my 2 cents...
The first is that I always put the where for local function definitions on a new line, e.g. foo x = x + a + b where a = 1 + x b = 2 * x I find this a lot clearer and prettier than, foo x = x + a + b where a = 1 + x b = 2 * x
I used to do it your style, but have switched to:
foo x = x + a + b where a = 1 + x b = 2 * x
because it makes cut&paste easier. instance/class declarations for me also don't obey this.
data AST = Const Int | Var String | Lam String AST | App AST AST | Let String AST AST | Add AST AST
same here. or for records, I like:
data Rec = Rec { foo :: Int, bar, bluff :: String }
Another difficult case that I haven't solidified a style for is large type signatures.
I tend to do something like:
myfoo :: (Context1, Context2, Context3) => type1 -> -- maybe a description of type1 type2 -> type3 -> result type
it takes a lot more vertical space, but you also have easy haddockability and it makes it a lot easier to remember what all those parameters are... - hal