
setref(+Name, ?Value)

   Sets the value of the named reference to Value.

Arguments
   Name                Atom (name of a reference).
   Value               Prolog term.

Type
   Non-logical Variables, Arrays, Bags, Shelves and Stores

Description
   If Name is the name of a (previously declared) reference, it will
   will be set to refer to the term Value.

   A named reference can be used to hold a reference to a term, in the
   same way as a logical variable.  Unlike a logical variable, the
   reference has a name under which it can be looked up.  Its value is
   not a copy, but a reference to the actual Value.  This implies that
   the value behaves logically, i.e. it disappears on backtracking,
   bindings to the variables inside it are undone on backtracking etc.

   Changing the value of a reference is similar to changing an argument of
   a compound term using setarg/3.  The change is undone on backtracking,
   i.e. the value of the reference reverts to what it was before being
   changed.  A reference that has never been set (or whose settings were
   all undone by backtracking) has its declared initialization value.

   Reference names are visible in the module where they are declared.
   Furthermore every ECLiPSe engine has its own reference store,
   meaning that the values are engine/thread-local and cannot be shared.


Modes and Determinism
   setref(+, ?) is det

Modules
   This predicate is sensitive to its module context (tool predicate, see @/2).

Exceptions
     4 --- Name is uninstantiated
     5 --- Name is not an atom.
    45 --- Name has not been declared as a reference.

Examples
   
    ?- local reference(r, hello).
    Yes (0.00s cpu)

    ?- getref(r,X), setref(r,world), getref(r,Y).
    X = hello
    Y = world
    Yes (0.00s cpu)

    ?- getref(r,X), ( setref(r,world), fail ; getref(r,Y) ).      
    X = hello
    Y = hello
    Yes (0.00s cpu)


See Also
   reference / 2, getref / 2, setarg / 3, swapref / 3
