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Funcons-beta : Linking.cbs | PRETTY | PDF

Linking 

[
  Datatype links
  Funcon   initialise-linking
  Funcon   link
  Funcon   fresh-link
  Funcon   fresh-initialised-link    Alias fresh-init-link
  Funcon   set-link
  Funcon   follow-if-link
]
Meta-variables
  T <: values
Datatype
  links ::= link(_:variables)
Funcon
  initialise-linking(X:=>T) : =>T
   ~> initialise-storing(X)

initialise-linking(X) ensures that the entities used by the funcons for linking are properly initialised.

Funcon
  fresh-link(T) : =>links
    ~> link(allocate-variable(T))
Funcon
  fresh-initialised-link(T, V:T) : =>links
    ~> link(allocate-initialised-variable(T, V))
Alias
  fresh-init-link = fresh-initialised-link
Funcon
  set-link(_:links, _:T) : =>null-type

The value of a link can be set only once.

Rule
  set-link(link(Var:variables), V:T) ~> initialise-variable(Var, V)
Funcon
  follow-link(_:links) : =>values
Rule
  follow-link(link(Var:variables)) ~> assigned(Var)
Funcon
  follow-if-link(_:values) : =>values

If V is a link, follow-if-link(V) computes the set value, and otherwise it evaluates to V.

Rule
  follow-if-link(link(Var:variables)) ~> assigned(Var)
Rule
  follow-if-link(V:~links) ~> V
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