It is possible to specify homogeneous vectors of things (e.g. lists
of numbers) using the repeated attribute. You specify a
repeated field as follows:
repeated(22, float([1,2,3,4])),
repeated(23, enum(tank_state([empty, half_full, full]))).
The first clause above, will cause all four items in the list to be encoded in the wire-stream as IEEE-754 32-bit floating point numbers, all with tag 22. The decoder will aggregate all items in the wire-stream with tag 22 into a list as above. Likewise, the all items listed in the second clause will be encoded in the wire-stream according to the mapping defined in an enumeration (described below) tank_state/2, each with tag 23.
Notes:
Beware that there is no explicit means to encode an empty set. The
protobuf specification provides that a repeated field may
match a tag zero or more times. The empty set, while legal, produces no
output on encode. While decoding a repeated term, failure
to match the specified tag will yield an empty set of the specified host
type.
The protobuf grammar provides a variant of the repeated
field known as "packed." Packed, repeated fields are currently not
supported by our interpreter.