17. The parser as claimed in claim 16 , wherein the combining means sequentially combines the parsing results for the respective fragments from left to right in a way of: (1) finding, in a second double-edge tree corresponding to a right fragment, an upward path from its start node to its root node as a second combining path, and determining a number of nodes on the second combining path; (2) finding, in a first double-edge tree corresponding to a left fragment, an upward path having a same number of nodes as the number of nodes upward from its end node as a first combining path; (3) combining corresponding nodes on the first and second combining paths to thereby combine the first and second double-edge trees so as to obtain a combined double-edge tree, and modifying a start node and an end node of the combined double-edge tree; and (4) repeating elements (1)-(3) for the combined double-edge tree and a double-edge tree corresponding to a next fragment.
16. The parser as claimed in claim 15 , wherein the double-edge tree includes a start node and an end node, and a flag indicating whether an error occurs when each of the fragments is parsed.