Determine the next token
function () {
			if (/\w/.test(this.currentChar)) return this.readWord();
			if (/["'`]/.test(this.currentChar)) return this.readString();
			if (/[()]/.test(this.currentChar)) return this.readGroupSymbol();
			if (/[!=<>]/.test(this.currentChar)) return this.readOperator();

			if (this.currentChar === "") return {type: 'eot', value: ''};
			else {
				this.readNextChar();
				return {type: 'empty', value: ''};
			}
		}