reuse choice expression in cases based on _result_ of match

[michaellilltokiwa]

match ss.accept
             e error => e
             sock Java.java.net.Socket =>
               match sock.getInputStream
                 e error => e
                 i Java.java.io.InputStream =>
                   input  := jio.BufferedReader.new (jio.InputStreamReader.new i)
                   match sock.getOutputStream
                     ...

this could be written as:

match ss.accept as accepted
             error => accepted
             Java.java.net.Socket =>
               match accepted
                 error => accepted
                 Java.java.io.InputStream =>
                   input  := jio.BufferedReader.new (jio.InputStreamReader.new accepted)
                   match accepted.getOutputStream as os
                     ...

another example:

str option String := "Hello"
match str
   s String => s.substring 0 2
   nil => say nil

would be

str option String := "Hello"
match str
   String => str.substring 0 2
   nil => say str

The main advantage I see in this is that programmers would not have to introduce new names all the time.
Disadvantage could be that this could potentially be confusing in larger nested match expressions.