<parms> -> "[" <idn_list> "]"
<where> -> where <restriction> ["," <restriction>]*
<restriction> -> <idn> has <nonparam_interface> [, <nonparam_interface>]*
<nonparam_interface> -> <idn> <nonparam_proc_sig> | <idn> <nonparam_iter_sig>
<nonparam_proc_sig> -> "(" [ <type_list> ] ")" [<returns>] [<signals>]
<nonparam_iter_sig> -> "(" [ <type_list> ] ")" <yields> [<signals>]
<type_list> -> <type_designator> ["," <type_designator>]*
All the parameters are types. The where clause
lists any restrictions on a parameter by stating methods that objects of the
parameter type must have. For example,
find [T] (a: collection[T], v: T) returns (int) signals (not_found)
where T has equal (T) returns (bool)
defines a parameterized routine with one parameter "T". Within the
parameterized definition, objects of a parameter type can be assumed
to have the methods listed in the where clause; any
instantiation of the parameterized definition will provide a binding
for each of these
methods (3.2.2,7.7).
Within the scope corresponding to a parameterized specification, parameter names can be used to denote types. If parameters are used in instantiations, any requirements of the parameterized types being instantiated must be met in the usual way. For example, consider the instantiation "collection[T]" used in the specification of [tex2html_wrap2956]find; if "collection" required an "lt" method, the Theta compiler would reject the specification of "find" because the instantiation of "collection" is illegal.
A parameterized type may have declared supertypes. For example
stack = type[T] < item, bag[T], stack_pair[T, int]states that every instantiation of stack is a subtype of "item" and of the corresponding instantiations of "bag" and "stack_pair" (e.g., "stack[foo]" is a subtype of "item", "bag[foo]", and "stack_pair[foo, int]"). There is no subtype/supertype relationship on parameters: for example, "stack[foo]" is not a subtype of "stack[bar]" even if "foo" is a declared subtype of "bar". Subtyping operates only ``outside the square brackets'' of a type definition.