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(define-library (csc compare)
(export diff)
(import (scheme base)
(only (csc format) fprintf)
(only (csc loop)
loop
return)
(only (csc match) match)
(only (csc sort) sort)
(only (csc strings)
contains
split)
(only (csc vec)
vec
vec-append))
(begin
; compare is inspired by Go's cmp.Diff.
(define (apply-transformer t x)
(if (list? t)
(loop for transformer in t
do (set! x (apply-transformer transformer x))
finally (return x))
(if ((car t) x)
((cdr t) x)
x)))
(define (alist? l)
(match l
(((key . _) . _)
(symbol? key))
(_ #f)))
(define (transform x transformers)
(define x* (apply-transformer transformers x))
(cond
((alist? x*)
(sort (lambda (a b) (string<? (symbol->string (car a)) (symbol->string (car b))))
(map (lambda (elem)
(cons (car elem) (transform (cdr elem) transformers)))
x*)))
((list? x*)
(map (lambda (elem) (transform elem transformers))
x*))
(else x*)))
; As always, I copied the algorithm from Wikipedia
(define (lcs x y cmp)
(define x-vals (list->vector x))
(define y-vals (list->vector y))
(define table (make-vector (* (+ 1 (vector-length x-vals)) (+ 1 (vector-length y-vals))) 0))
(define (index i j)
(+ j (* i (+ 1 (vector-length y-vals)))))
(loop for i from 1 to (vector-length x-vals)
do (loop for j from 1 to (vector-length y-vals)
if (cmp (vector-ref x-vals (- i 1)) (vector-ref y-vals (- j 1)))
do (vector-set! table (index i j) (+ 1 (vector-ref table (index (- i 1) (- j 1)))))
else
do (vector-set! table (index i j) (max (vector-ref table (index (- i 1) j))
(vector-ref table (index i (- j 1)))))))
(let loop ((i (vector-length x-vals))
(j (vector-length y-vals))
(lcs '()))
(cond
((or (= 0 i) (= 0 j)) lcs)
((cmp (vector-ref x-vals (- i 1)) (vector-ref y-vals (- j 1)))
(loop (- i 1) (- j 1) (cons (vector-ref x-vals (- i 1)) lcs)))
((> (vector-ref table (index i (- j 1))) (vector-ref table (index (- i 1) j)))
(loop i (- j 1) lcs))
(else (loop (- i 1) j lcs)))))
(define (pretty w x indent)
(cond
((and (pair? x)
(symbol? (car x)))
(fprintf w "{} ({} .\n" indent (car x))
(pretty w (cdr x) (string-append indent " "))
(fprintf w "{} )\n" indent))
((list? x)
(fprintf w "{} (\n" indent)
(loop with new-indent = (string-append indent " ")
for v in x
do (pretty w v new-indent))
(fprintf w "{} )\n" indent))
(else (fprintf w "{} {}\n" indent x))))
(define (diff* w x y indent)
(cond
((or (and (boolean? x) (boolean? y))
(and (char? x) (char? y))
(and (symbol? x) (symbol? y))
(and (number? x) (number? y))
(and (string? x) (string? y)))
(if (equal? x y)
(begin
(fprintf w "{} {}\n" indent x)
#t)
(begin
(fprintf w "{}- {}\n{}+ {}\n" indent x indent y)
#f)))
((and (alist? x) (alist? y))
(fprintf w "{} (\n" indent)
(let ((key-lcs (lcs (map car x) (map car y) symbol=?))
(indent* (string-append indent " "))
(equal #t))
(loop if (null? key-lcs)
if (null? x)
if (null? y)
do (return)
else
do (pretty w (car y) (string-append indent* "+"))
(set! y (cdr y))
(set! equal #f)
else
do (pretty w (car x) (string-append indent* "-"))
(set! x (cdr x))
(set! equal #f)
else
if (symbol=? (caar x) (caar y) (car key-lcs))
do (fprintf w "{} ({} .\n" indent* (car key-lcs))
(set! equal (and (diff* w (cdar x) (cdar y) (string-append indent* " "))
equal))
(fprintf w "{} )\n" indent*)
(set! x (cdr x))
(set! y (cdr y))
(set! key-lcs (cdr key-lcs))
else if (symbol=? (caar x) (car key-lcs))
do (pretty w (car y) (string-append indent* "+"))
(set! y (cdr y))
(set! equal #f)
else
do (pretty w (car x) (string-append indent* "-"))
(set! x (cdr x))
(set! equal #f))
(fprintf w "{} )\n" indent)
equal))
((and (list? x) (list? y))
(fprintf w "{} (\n" indent)
(let* ((common (lcs x y equal?))
(indent* (string-append indent " "))
(equal #t))
(loop if (null? common)
if (null? x)
if (null? y)
do (return)
else
do (pretty w (car y) (string-append indent* "+"))
(set! y (cdr y))
(set! equal #f)
else if (null? y)
do (pretty w (car x) (string-append indent* "-"))
(set! x (cdr x))
(set! equal #f)
else
do (diff* w (car x) (car y) indent*)
(set! x (cdr x))
(set! y (cdr y))
(set! equal #f)
else
if (equal? (car x) (car y))
do (pretty w (car x) (string-append indent* " "))
(set! x (cdr x))
(set! y (cdr y))
(set! common (cdr common))
else if (equal? (car x) (car common))
do (pretty w (car y) (string-append indent* "+"))
(set! y (cdr y))
(set! equal #f)
else if (equal? (car y) (car common))
do (pretty w (car x) (string-append indent* "-"))
(set! x (cdr x))
(set! equal #f)
else
do (diff* w (car x) (car y) indent*)
(set! x (cdr x))
(set! y (cdr y))
(set! equal #f))
(fprintf w "{} )\n" indent)
equal))))
(define default-transformers
(list
(cons (lambda (s)
(and (string? s)
(contains s "\n")))
(lambda (s)
(list (cons '!type 'string)
(cons 'value (split s "\n")))))
(cons vector? (lambda (v)
(list (cons '!type 'vector)
(cons 'value (vector->list v)))))
(cons bytevector? (lambda (b)
(list (cons '!type 'bytevector)
(cons 'value (loop for i below (bytevector-length b)
collect (string-append "0x" (number->string (bytevector-u8-ref b i))))))))))
; Returns a string diff between x and y. Diff knows how to compare lists,
; alists and other primitive types. Any user-defined type needs a
; transformer. Each transformer is a pair of type predicate that the
; transformer matches on, and a function that transforms a value of that
; type into an alist.
(define (diff x y . transformers)
(define d (open-output-string))
(define t* (cons default-transformers transformers))
(if (diff* d (transform x t*) (transform y t*) "")
""
(get-output-string d)))))
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