The Fortress Language Specification - CiteSeerX

swap(x :Object, y : Object) = (y, x)
Similarly, function parameter type can often be inferred from the body of the function. When a type can be inferred
for a parameter from the body of the function, that parameter type need not be declared explicitly. Thus, the following
declaration of swap has the same parameter type and return type as the above declarations:
swap(x, y) = (y, x)
See Chapter 20 for a discussion of type inference in Fortress.
The following function wrap :
wrap(xs,ys = xs) = [xs ys]
returns an array containing its parameters. If a value for only the parameter xs is given to wrap at a call site, the value
of xs is bound to ys as well, and an array that contains xs as both of its indices is returned.
12.2 Function Applications
Fortress provides overloaded functions (as described in Chapter 15); there may be multiple function declarations with
the same function name in a single lexical scope. Thus, we need to determine which function declaration are applicable
to a function application.
If a function’s argument type is () , then function declarations with the following forms of parameter lists are considered
to be applicable:
• () which means the same thing as ( : ())
• (x :()) which is something programmers don’t ordinarily write
• (x :T . . .)
In the last case, x is bound to an empty HeapSequenceT .
If a function’s argument type A is neither () nor a tuple type, then function declarations with the following forms of
parameter lists are considered to be applicable:
• (x :T) where A is a subtype of T
• (x :T . . .) where A is a subtype of T
In the last case, x is bound to a HeapSequenceT of length 1 , containing the actual argument value.
If a function’s argument type A is a tuple type, then function declarations with the following forms of parameter lists
are considered to be applicable:
• (x :T) where A is a subtype of T
• (x :T . . .) where A is a subtype of T
• a parameter list with no varargs binding, provided that
– type A has exactly as many plain types as the parameter list has plain bindings, and
– for every keyword-type pair (described in Section 8.4) in A, the parameter list has a binding with the same
keyword, and
– for every element type in A, the type in the element type is a subtype of the type of the corresponding
binding in the parameter list.
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