EXDR defines the abstract data types Integer, Long, Double, String, List, Nil, Struct and Anonymous Variable. Their mapping to ECLiPSe data types is as follows:
EXDR type ECLiPSe type e.g. ---------------------------------------------- Integer integer 123 Long integer 10000000000 Double float 12.3 String string "abc" List ./2 [a,b,c] Nil /0  Struct compound or atom foo(bar,3) Anon.Variable var _The type of the generated EXDR-term is the type resulting from the "natural" mapping of the Eclipse terms. Atoms are written as structures of arity 0 (not as strings).
Not all ECLiPSe terms have an EXDR representation, e.g. integers longer than 64 bits, rationals, suspensions or improper lists. The predicate fails in this case, nevertheless writing a complete but simplified term to the stream. All information about variable sharing and variable attributes in the ECLiPSe term is silently lost (no failure).
Note that as with all output predicates, the output may be buffered, so it may be necessary to flush either by closing the stream or by using flush/1.
If the output Stream has the compress-flag set, write_exdr/2 will use a more compact variant of EXDR encoding, at the expense of encoding speed.
More information about EXDR format, including the specification of the serialised encoding, can be found in the Embedding and Interfacing Manual.
Success: ?- open(queue(""),update,q), write_exdr(q, foo(12.3,123,["hello",_])), read_exdr(q, Term), close(q). Term = foo(12.3, 123, ["hello", _131]) yes. Failure: write_exdr(q, 617236126172). write_exdr(q, 3_4). Error: write_exdr(S, a(b,c)). (Error 4). write_exdr(input, X + 2). (Error 192). write_exdr(atom, X + 2). (Error 193).