What indentation is required for a case statement within a let statement?

Question

Working in haskell, found odd behavior, stripped it down to bare bones

This Works

a :: Bool
a = case True of
    True -> True
    False -> Fals         


        

Answer 1

I don't have the exact wording from the spec, but this Wikibook page explains the issue quite clearly.

The reason why it works like this is simple: to support binding multiple variables via a single let-group, such as:

c = do
    let c' = …
        d  = …
        e  = …
    return c'

Your True -> … and False -> … are mistakenly interpreted as additional variables to be bound.