A language processing system uses a lattice parser that semantically parses a command input represented by a lattice. The parser receives a hypotheses space of outputs as encoded in a lattice. Annotations of the input are projected back into the lattice and then lattice parsing is performed to rectify with the annotations. Parsing rules are applied to path fragments in the lattice. The rules that successfully parse from the start node to the end node of the lattice are used to determine whether the command input sentence invokes a specific action, and if so, what arguments are to be passed to the invocation of the action.