protected boolean atListEnd() {
            skipSpace();
            if (position >= string.length()) {
                throw new IllegalArgumentException("At value position " + position + ": Expected a ']'" +
                        " but got the end of the string");
            }
            return string.charAt(position) == ']';
        }
Parses unbound tensor short forms - e.g. tensor(x[],y[]):[[1,2,3],[4,5,6]]
vespajlib/src/main/java/com/yahoo/tensor/TensorParser.java