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.