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Writing of soft-typing: <constructor name> is bound to a procedure that takes as many arguments as there are <field tag>s in the (<constructor name> ...) subform and returns a new <type name> record. Fields whose tags are listed with <constructor name> have the corresponding argument as their initial value. The initial values of all other fields are unspecified. It is a good idea to allow extra fields, but I would like to see that they are initialized with a value. A soft typer will otherwise analyze this field with "undefined" or something like this, and potentially every access to the field will be "polluted." Even a good flow-sensitive analysis will often not make a difference. That's our experience. -- Matthias