Compound expressions

compound_expression:
          `{' top_expression_list `}'
        ;

A compound_expression is a sequence of top expressions. The type and value of the compound_expression is the type and value of the last expression it contains. The value to be returned from a method is not the value of its method_body compound. A separate return_expression exists to assign the method return value (see section Jumps and returns).

top_expression_list:
          top_expression [`;' top_expression_list]
        ;

Note that the semicolon is a separator, not a terminator.

top_expression:
          local_var_decl
        | expression
        ;

A local_var_decl (see section Local variables) is not an expression because that is unnecessary:

• The expression int a = 1 can equally well be used without the int a = if the a is not used anywhere else, or, it can be braced: { int a = 1 }. If it is used somewhere else, the declaration can be put in the enclosing compound and then, obviously, the plain assignment a = 1 can be used as an expression.
• For the expression int a = 1, b = a + 1, the expression { int a = 1; a + 1} can be used with exactly the same semantics. Remarks from the previous item are also valid for this case.
• The real reason for not letting a local_var_decl be a normal expression is because it would make typing a tuple unclear. For example, if int a = 1, b = 2 were an expression, the type of the tuple

  (q = 1, 2, int a = 3, b = 4, 5)
  

  would depend on rules concerning the precedence of the comma in tuple and local_var_decl, i.e. the precedence of the comma would depend on its context. Since this is not considered a good idea and because of the limited usefulness of the local_var_decl being an expression (as shown in the preceding paragraphs), the local_var_decl is not an expression.

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