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cl-difflibtext-processingutils

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This library is able to compute differences between sequences. For example, if we want to generate a unified diff for two lists of strings, we can do:

POFTHEDAY> (difflib:unified-diff
            t
            '("one" "two" "three" "four" "five" "six")
            '("one" "three" "four" "seven" "eight")
            :test-function 'equal)

---  
+++  
@@ -1,6 +1,5 @@
 one
-two
 three
 four
-five
-six
+seven
+eight

It is also possible to provide filenames:

POFTHEDAY> (difflib:unified-diff
            t
            '("one" "two" "three" "four" "five" "six")
            '("one" "three" "four" "seven" "eight")
            :test-function 'equal
            :from-file "a.txt"
            :to-file "b.txt")

--- a.txt 
+++ b.txt 
@@ -1,6 +1,5 @@
 one
-two
 three
 four
-five
-six
+seven
+eight

There is also a lower-level API. We can make a diff of any objects. Here is an example of how to get a diff of two lists of symbols:

POFTHEDAY> (defparameter *diff*
             (make-instance 'difflib:sequence-matcher
                            :a '(:one :two :three :four :five :six)
                            :b '(:one :three :four :seven :eight)))

POFTHEDAY> (difflib:get-opcodes *diff*)
(#<DIFFLIB:OPCODE :EQUAL   0 1 0 1>
 #<DIFFLIB:OPCODE :DELETE  1 2 1 1>
 #<DIFFLIB:OPCODE :EQUAL   2 4 1 3>
 #<DIFFLIB:OPCODE :REPLACE 4 6 3 5>)

These "opcodes" tell us what to do with subsequences of two lists. For example, REPLACE opcode from the results tell us that:

;; This should be replaced:
POFTHEDAY> (subseq '(:one :two :three :four :five :six)
                   4 6)
(:FIVE :SIX)

;; with:
POFTHEDAY> (subseq '(:one :three :four :seven :eight)
                   3 5)
(:SEVEN :EIGHT)

;; The same as we seen in the text output in the beginning:
--- a.txt 
+++ b.txt 
@@ -1,6 +1,5 @@
 one
-two
 three
 four
-five
-six
+seven
+eight

Tomorow we'll see the library, which uses cl-difflib for something more interesting.