Declarations

Declarations take several forms:

declaration:
	identifier-list : type;
	identifier-list : type = expression;
	identifier := expression;
	( id-or-nil-list ) := expression; 
	identifier-list : con expression;
	identifier-list : import identifier;
	identifier-list : type type;
	include string-constant;

identifier-list:
	identifier
	identifier-list, identifier

expression-list:
	expression
	expression-list, expression