The Fortress Language Specification - CiteSeerX

11.2 Nat and Int Parameters
Syntax:
StaticParam ::= nat Id
| int Id
Static parameters may include one or more nat and int parameters. Syntactically, a nat parameter consists of the
special reserved word nat followed by an identifier. An int parameter consists of the special reserved word int
followed by an identifier. These parameters are instantiated at runtime with numeric values. A nat parameter may
be used to instantiate other nat parameters, or to appear in any context that a variable of type N can appear, except
that it cannot be assigned to. An int parameter may be used to instantiate other int parameters, or to appear in any
context that a variable of type Z can appear, except that it cannot be assigned to.
For example, the following function f :
fnat n(x :Length 2n ) :Length n = sqrt(x)
declares a nat parameter n , which appears in both the parameter type and return type of f .
11.3 Bool Parameters
Syntax:
StaticParam ::= bool Id
Static parameters may include one or more bool parameters. Syntactically, a bool parameter consists of the special
reserved word bool followed by an identifier. These parameters are instantiated at runtime with boolean values. They
may be used to instantiate other bool parameters, or to appear in any context that a variable of type Boolean can
appear, except that they cannot be assigned to.
For example, the following coercion declared in the trait Boolean:
trait Boolean
coercion bool b(x: BooleanLiteralb)
end
declares a bool parameter b , which appears in the parameter type. See Chapter 24 for a full declaration of Boolean.
11.4 Dimension and Unit Parameters
Syntax:
StaticParam ::= dim Id
| unit Id [ : DimRef ] [absorbs unit ]
Static parameters may include one or more dim and unit parameters. Syntactically, a dim parameter begins with
the special reserved word dim followed by an identifier. A unit parameter begins with the special reserved word
unit followed by an identifier, optionally followed by the token : and a dimension, and the unit is thereby restricted
to be a unit of the specified dimension. A unit parameter may include the clause “absorbs unit ”; the meaning of
this is described in Section 35.4. A dim parameter is allowed to appear in any context that a dimension can appear. A
unit parameter is allowed to appear in any context that a unit can appear.
For example, here is a function that is parameterized with a unit:
sqrtunit U(x: R64 U 2 ): R64 U = numericalsqrt(x/U 2 ) U
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