This is a Common Lisp port of Neil Fraser's Diff, Match and Patch library (http://code.google.com/p/google-diff-match-patch/). It implements operations required for synchronizing sequences of Lisp objects, in particular plain text represented as character strings. The operations fall into three subtasks: 1. Diff: Compare two sequences and return a list of differences (edit operations). Diff implements Gene Myers's 1986 algorithm with complexity O(N * D), where N is the sum of lengths of the two sequences, and D is the size of the shortest edit script. 2. Match: Given a search sequence, find a (possibly fuzzily) matching subsequence of another sequence near a given position. Match implements the Bitap algorithm, as described by Wu and Manber (1991). Its broad idea is to search the space around the position first for an exact occurence of the search pattern, then for a subsequence which matches the pattern with one error, then with two errors, etc. If two or more matches are found, they are compared by a score which trades off proximity and number of errors. 3. Patch: Create a list of contextualized edit operation groups (?hunks?) corresponding to a diff of two sequences A and B; apply it to a third sequence A? in order to produce an equivalent edit B?. A hunk recording the changes of a subsequence S of A can be applied to a subsequence S? of A? both when S and S? are equal, and when S? is a fuzzy match of S in A? near the position indicated by the hunk, and the badness of the match (computed as the Levenshtein distance between S and S? divided by the length of S) is reasonably low. The library defines the package DIFF-MATCH-PATH (nicknamed DMP), which exports the following names: {function} DIFF A B &KEY (TEST #'EQL) Find the differences between two sequences A and B of elements comparable under the function TEST. Return a list of edit operations of the form (OP X), where OP is one of the keywords :+ :- :=, and X is a subsequence of A or B. {parameter} *DIFF-TIMEOUT* Number of seconds to refine a diff before giving up (NIL for infinity). Initial value = 5.0. {parameter} *DIFF-EDIT-COST* Cost of an empty edit operation in terms of edit characters. Used to detect operationally trivial equalities when cleaning up diff lists. Initial value = 4. {parameter} *DIFF-CHECK-LINES-LENGTH* When a diff is computed between strings, how long should they be to to qualify for line-level-diff optimization. On strings whose length is greater than this value, a line-level diff is run first to identify the changed areas. NIL = don't optimize. Initial value = 1000. {function} MAPDIFF FN DIFFS Return a copy of edit operation list DIFFS in which the content of every operation has been replaced by its image under FN. {function} DIFF-ORIGIN DIFFS Given a difference list, rebuild the first of the compared sequences. {function} DIFF-DESTINATION DIFFS Given a difference list, rebuild the second of the compared sequences. {function} TRANSLATE-POSITION DIFFS POSITION Given the difference list DIFFS between two sequences and a POSITION in the first sequence, return the equivalent position in the second sequence. {function} LEVENSHTEIN DIFFS Given the difference list DIFFS between two sequences, return the corresponding Levenshtein distance. {function} INDEX-ABBREVIATOR &OPTIONAL (HASH-TABLE-TEST #'EQUAL) Return two unary functions: one to abbreviate things to integers, the other to restore them from integer abbreviations. {function} MATCH SPACE PATTERN POSITION &KEY (TEST #'EQL) Locate a subsequence most closely resembling PATTERN in SPACE near POSITION. {parameter} *MATCH-THRESHOLD* At what point is no match declared (0.0 = perfection, 1.0 = very loose). Initial value = 0.5. {parameter} *MATCH-DISTANCE* How far to search for a match (0 = exact location, 1000+ = broad match). A match this many characters away from the expected location will add 1.0 to the error score (0.0 is a perfect match). Initial value = 1000. {function} MAKE-PATCH A B &KEY (TEST #'EQL) MAKE-PATCH &KEY DIFFS (TEST #'EQL) When called with two seuqences A and B, compute the diff between them and convert it into a list of hunk objects. Alternatively, the diff can be passed explicitly by keyword argument, and sequences reconstructed from it. {function} WRITE-CHARS-PATCH PATCH &OPTIONAL (OUT *STANDARD-OUTPUT*) Write the formatted representation of the given PATCH (a hunk or list of hunks, encoding a difference of character strings) to the stream OUT. {function} READ-CHARS-PATCH &OPTIONAL (IN *STANDARD-INPUT*) Read a formatted representation of patch encoding a difference of character strings from the stream IN and return it as a list of hunks. {function} WRITE-LINES-PATCH PATCH &OPTIONAL (OUT *STANDARD-OUTPUT*) Write the formatted representation of the given PATCH (a hunk or list of hunks, encoding a difference of line sequences) to the stream OUT. {function} READ-LINES-PATCH &OPTIONAL (IN *STANDARD-INPUT*) (SEQ-TYPE 'VECTOR) Read a formatted representation of patch encoding a difference of line sequences from the stream IN and return it as a list of hunks. The type of line sequences in hunk difference lists is determined by the parameter SEQ-TYPE (which normally should be one of the symbols VECTOR or LIST). {class} HUNK {accessor} HUNK-DIFFS HUNK {accessor} HUNK-START-A HUNK {accessor} HUNK-START-B HUNK {accessor} HUNK-LENGTH-A HUNK {accessor} HUNK-LENGTH-B HUNK A wrapper for an edit or group of adjacent edits. {function} APPLY-PATCH PATCH SEQ &KEY (PADDING #'DMP::TRIVIAL-PADDING) (TEST #'EQL) Apply PATCH (a list of hunks) to the sequence SEQ. Return two values: (1) SEQ, or its modified copy; and (2) a list of booleans, of the same length as PATCH, indicating for every hunk if it could be applied. {parameter} *PATCH-DELETE-THRESHOLD* When deleting a large block of text (over ~64 characters), how close do the contents have to be to match the expected contents. (0.0 = perfection, 1.0 = very loose). Note that *MATCH-THRESHOLD* controls how closely the end points of a delete need to match. Initial value = 0.5. {parameter} *PATCH-MARGIN* Chunk size for context length. Initial value = 4. {parameter} *MAX-BITS* The number of bits in an int, used to limit the width of match patterns when applying an inexact patch.Initial value = (INTEGER-LENGTH MOST-POSITIVE-FIXNUM). Common Lisp having bigints allows to set this value to NIL (meaning unlimited width), but keeping it as it is optimizes performance by using fixints only.

- Author
- Neil Fraser; ported by Boris Smilga
- Maintainer
- Boris Smilga <boris.smilga@gmail.com>
- License
- Apache 2.0