Randal L. Schwartz wrote:
>>>>>> "Igor" == Igor Stasenko <siguctua at gmail.com> writes:
> 
> Igor> Just wonder, if following is correct expression:
> Igor> | t |
> Igor> 1 + t := 5
> 
> It seems to me that that should be wrong, because to me the assignment
> operation is very low precedence. And the binary message send would therefore
> be out of place. If it wasn't illegal already, I'd argue to make it illegal,
> as it would lead to misleading code.

Yes, it should be wrong.  The grammar is:

   expression: keyword_expression cascaded_sends
      | variable ':=' expression

   keyword_expression: binary_expression
      | binary_expression keyword_send

   binary_expression: unary_expression
      | binary_expression binary_send

   unary_expression: primary_expression
      | unary_expression unary_send

   primary_expression: literal
      | variable
      | '(' expression ')'

   cascaded_sends: cascaded_sends ';' message_send
      | /* empty */

   message_send: keyword_send
      | binary_send
      | unary_send

   variable: IDENTIFIER
   unary_send: IDENTIFIER
   binary_send: BINOP unary_expression
   keyword_send: KEYWORD binary_expression
      | keyword_send KEYWORD binary_expression

So ':=' can only appear at toplevel or inside parentheses, and the above
is not valid.

Paolo