[Haskell-cafe] Empty case alternative

[Frantisek Farka]

Hello cafe,

I was looking into Haskell Report 2010 and notice something in the
definition of case statement:

https://www.haskell.org/onlinereport/haskell2010/haskellch3.html#x8-460003.13

Apparently an empty alternative within case statement is a plausible
production. ('alt' production rule, third option).

If I get it correctly, following example shows the empty alternative:

> 
> cStmt e = case e of { 'a' -> True ; {-- empty here --} ; 'b' -> False }
>

What I miss is any ratio behind this. What is the empty alternative
good for? Any idea?

Franta