Nested case statements in SML

Question

This is more of a stylistic question than anything else. Given the following piece of code:

case e1 of                    (* datatype type_of_e1  = p1 | p2 *)
           


        

Answer 1

Plain and short answer: no. But what's wrong with parentheses?

(Of course, you can also bracket in other ways, e.g. with a 'let', or by factoring into auxiliary functions, but parentheses are the canonical solution.)

Answer 2

No. The syntactic rules in the Definition of Standard ML state that the match arms of a case expression attempt to maximally consume potential clauses. And since there's no "end case" or similar marker in the language, the parser will merrily eat each of the "| pat => exp" clauses that you feed it until it sees something that terminates a list of match clauses.

Answer 3

The answer is "(" and ")". My example:

case e1 of                   
   p1 => ( case e11 of         
              NONE => expr11
              | SOME v => expr12 v )
   | p2 => ( case e21 of         
                NONE => expr21
                | SOME v => expr22 v )

This really works! Cool :) You can try it too.