Cases expressions don't work

[Pytheas01]

Consider the following function in SymphonyTool 0.4:

headAndTail: seq of nat -> seq of nat
headAndTail(l) ==
cases l:
[] -> []
[h] ^ l2 -> l2
end

The following error message appears to the left of the empty sequence case:

no viable alt; token=[@735,2364:2365='[]',<72>,144:4](decision=171 state 0) decision=<<>>.