// getFunction returns a function for a name
sO ai_evalFunctionCallLHS(BasicLogicRule rule, IF1 getFunction) {
  if (rule.lhs instanceof FunctionCall) {
    FunctionCall fc = cast rule.lhs;
    O f = getFunction.get(fc.function);
    if (f == null) null;
    ret callF(f, fc.args);
  }
  null;
}