These methods, respectively, set
and query the “valued status” of a symbol.
Once set to a value with the
the valued status of a symbol is “locked” at that value.
It cannot thereafter be changed.
Subsequent calls to
for the same sym_id will fail,
leaving sym_id’s valued status unchanged,
unless value is the same as the locked-in value.
Return value: On success, 1 if the symbol symbol_id is valued after the call, 0 if not. If the valued status is locked and value is different from the current status, -2. If value is not 0 or 1; or on other failure, -2.