用警卫替换 where 的情况

Question

I have specific situation I've checked a link here and I was wondering if the same strategy could be applied within a where statement in haskell.

Suppose I have a function:

Func1:: Term -> [Term]
Func1 (Foo a b) = [ Foo a' b | a' <- Func1a ] ++ [ Foo b' a | b' <- Func1b ] ++ M
   where
   M = case a of
      Bar v body -> [substitute var b body]
      _               -> []   

Is there a way to replace the case of with guards?

Answer 1

Here's how you can do it:

func1 :: Term -> [Term]
func1 (Foo a b) = [ Foo a' b | a' <- func1a ] ++ [ Foo b' a | b' <- func1b ] ++ m
  where
    m | Bar v body <- a = [substitute v b body]
      | otherwise       = []   

I think the main point of confusion might be that you can place the | immediately after m . The rest it is very similar to the answer that you already linked.