A pattern may have parameters, which may be data-items or virtual patterns.
Data-items may be normal objects or value objects. See the Section on objects and values for a description of the difference. See also the Section on Declarations.
Constant parameter
A constant data-item describing a value object may be specified as follows using the keyword val.
foo(..., X: val T, ...):
...An actual patrameter must be specified as part of the generation of an instance of foo as in
foo(..., aT, ...)In the body of foo, X is constant and may not be assigned new values.
A constant data-item describing a normal object may be specified as follows using the keyword obj:
foo(..., X: obj T, ...):
...Variable parameter
A variable data-item describing a value object may be specified as follows using the keyword var.
foo(..., X: var T, ...):
...An actual patrameter must be specified as part of the generation of an instance of foo as in
foo(..., aT, ...)In the body of foo, X is variable and may be assigned new values.
A variable data-item describing a reference to a normal object may be specified as follows using the keyword ref:
foo(..., X: ref T, ...):
...Virtual patterns as parameters
A pattern may have a virtual pattern as a parameter and a binding of the virtual pattern must be supplied when an instance is generated.
with(V: var integer):do(body:< Action):
...The parameter body is a virtual pattern qualified by he pattern Action. An invocation of %with%do% may have one of the following forms:
with (exp) :do (myAction)where myAction is subpattern of Action. Or:
with (exp) :do
item1
item2
item3where the argument following :do is an implicit subpattern of Action having the form:
Action
item1
item2
item3Example
An array pattern may be specified as follows:
array(range: var integer, elm:< Object):
...An instance of array may be declared as follows:
A: = array(100,Integer)Grammar
<Parameter> ::= <Declaration>Se Section 4. Declarations.