The Fortress Language Specification - CiteSeerX

(−b + sqrt(b 2 − 4ac))/2a
n n e (−n) sqrt(2πn)
a k b n−k
x 1 y 2 − x 2 y 1
1/2gt 2
n(n + 1)/2
(j + k)!/(j!k!)
1/3 3/5 5/7 7/9 9/11
17.3 meter/second
17.3 m/s
u · (v × w)
(A ∪ B)INTERSECT C
(A ∪ B) ∩ C
i < j ≤ k ∧ p ≺ q
print(“The answers are ” (p + q) “ and ” (p − q))
〈2, 3, 4, 5〉
13.9 Object Expressions
Syntax:
Val ::= object [Extends] (FldDef | MdDef ) ∗ end
Object expressions denote object values; they do not require evaluation. Syntactically, they start with the special
reserved word object , followed by an optional extends clause, field declarations, method declarations, and finally
the special reserved word end . The type of an object expression is an anonymous object trait type that extends
the traits listed in the extends clause of the object expression. The object trait type does not include the methods
introduced by the object expression (i.e., those methods not provided by any supertraits of the object expression).
Every evaluation of an object expression has the same anonymous object trait type. Each object trait type is associated
with a program location; any two object expressions with the same extends clause have different object trait types.
Unlike object declarations (described in Chapter 10), object expressions are not allowed to include modifiers nor value
parameters nor static parameters nor where clauses (described in Chapter 11). While object declarations must not
include any free static variable (i.e., all static variables in an object declaration must occur either as a static parameter
or as a where -clause variable), object expressions may include free static variables.
For example, the following object expression:
fT(x :T) = object f : T = x end
has a static variable T that is not its static parameter nor its where -clause variable.
The following example expression evaluates to a new object extending trait List:
object extends { List }
first() = throw Error
rest() = throw Error
cons(x) = Cons(x,self)
append(xs) = xs
end
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