Note that you can observe this effect with not just do, but also let, if, \, case, the extensions mdo and proc…and the dread unary -. I cannot think of a case in which this is ambiguous except for unary -. Here’s how the grammar is defined in the Haskell 2010 Language Report, §3: Expressions. … Read more
To see why you get the particular answers that arise, the desugaring explanations are very helpful. Let me supplement them with a little general advice about developing perceptions of Haskell code. Haskell’s type system makes no distinction between two separable “moral” purposes: [x] the type of values which are lists with elements drawn from x … Read more
do notation in Haskell desugars in a pretty simple way. do x <- foo e1 e2 … turns into foo >>= \x -> do e1 e2 and do x e1 e2 … into x >> do e1 e2 …. This means you can really write any monadic computation with >>= and return. The only reason … Read more