The Fortress Language Specification - CiteSeerX

α, β type variables
f
method name
x
field name
T
trait name
O
object name
C
trait or object name
τ, τ ′ , τ ′′ ::= α type
| σ
σ ::= N type that is not a type variable
| O −→ τ
N, M, L ::= T −→ τ super trait
| Object
K, H, J ::= α bound on a type variable
| N
e ::= x expression
| self
| O −→ τ ( −→ e )
| e.x
| eas C −→ τ .f −→ τ ( −−−→ eas τ)as τ
| typecase x = ein −−−→ τ ⇒ eelse eend
−−−−−−−−−−−→
fd ::= fαextends { −→ K}( −→ x:τ):τ = e
method definition
−−−−−−−−−−−→
td ::= trait Tαextends { −→ K}extends { −→ −−−−−−−−−−−→
N }where { αextends { −→ K}} −→ fd end trait definition
−−−−−−−−−−−→
od ::= object Oαextends { −→ K}( −→ x:τ)extends { −→ −−−−−−−−−−−→
N }where { αextends { −→ K}} −→ fd end object definition
d ::= td definition
| od
p ::= −→ d e program
Figure A.6: Syntax of Core Fortress with Where Clauses
A.2.3
Static Semantics
A static semantics for Core Fortress with Where Clauses is provided in Figures A.9, A.10, A.11, and A.12.
For simplicity, we use the following conventions:
• FTV (τ) collects all free type variables in τ.
• Similarly, FTV (e) collects all free type variables in all types in e.
We proved the type soundness of Core Fortress with Where Clauses using the standard technique of proving a progress
theorem and a subject reduction theorem.
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