How to factor out duplication code Haskell ( Maybe & If-Else)

• the fruit is a Maybe type
• if fruit is a apple and it is sweet (test with function testSweet) ,then trigger process A
• if it is not sweet or fruit is Nothing, then go with process B

Here is the dummy code,

   case fruit of 
       Just apple ->
           if testSweet apple then 
               <ProcessA>
           else
               <ProcessB>
       Nothing ->
               <ProcessB>

But it looks duplication here , any way to fix this ? I think the optimal way there should be only one <ProcessB> in the code.

You can use a guard and a catch-all fallback:

case fruit of 
   Just apple | testSweet apple ->
      <ProcessA>
   _ ->
      <ProcessB>

The last case _ will match both Nothing and Just non_sweet cases.