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(define-library (csc compare)
(export diff apply-transformer)
(import (scheme base)
(only (scheme write)
display
write)
(only (csc strings)
contains?
split))
(begin
; compare is inspired by Go's cmp.Diff.
(define (print w . xs)
(unless (null? xs)
(let ((x (car xs)))
(if (or (string? x)
(symbol? x))
(display x w)
(write x w)))
(apply print w (cdr xs))))
(define (apply-transformer t x)
(if (list? t)
(let loop ((transformers t)
(x x))
(if (null? transformers)
x
(loop (cdr transformers)
(apply-transformer (car transformers) x))))
(if ((car t) x)
((cdr t) x)
x)))
(define (alist? l)
(and (list? l)
(let loop ((l l))
(cond
((null? l) #t)
((not (and (pair? (car l))
(symbol? (caar l))))
#f)
(else (loop (cdr l)))))))
(define (transform x transformers)
(define x* (apply-transformer transformers x))
(cond
((alist? x*)
(map (lambda (elem)
(define elem* (apply-transformer transformers elem))
(if (pair? elem*)
(cons (car elem) (transform (cdr elem) transformers))
elem*))
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)))))
(let loop-i ((i 1))
(when (<= i (vector-length x-vals))
(let loop-j ((j 1))
(when (<= j (vector-length y-vals))
(if (cmp (vector-ref x-vals (- i 1)) (vector-ref y-vals (- j 1)))
(vector-set! table (index i j) (+ 1 (vector-ref table (index (- i 1) (- j 1)))))
(vector-set! table (index i j) (max (vector-ref table (index (- i 1) j))
(vector-ref table (index i (- j 1))))))
(loop-j (+ 1 j))))
(loop-i (+ 1 i))))
(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
((list? x)
(print w indent " (\n")
(let ((new-indent (string-append indent " ")))
(for-each (lambda (v)
(pretty w v new-indent))
x))
(print w indent " )\n"))
((and (pair? x)
(symbol? (car x)))
(print w indent " (" (car x) " .\n")
(pretty w (cdr x) (string-append indent " "))
(print w indent " )\n"))
(else (print w indent " " x "\n"))))
(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
(print w indent " " x "\n")
#t)
(begin
(print w indent "- " x "\n" indent "+ " y "\n")
#f)))
((and (alist? x) (alist? y))
(print w indent " (\n")
(let ((key-lcs (lcs (map car x) (map car y) symbol=?))
(indent* (string-append indent " "))
(equal #t))
(let loop ()
(unless (and (null? key-lcs)
(null? x)
(null? y))
(cond
((and (null? key-lcs)
(null? x))
(pretty w (car y) (string-append indent* "+"))
(set! y (cdr y))
(set! equal #f))
((null? key-lcs)
(pretty w (car x) (string-append indent* "-"))
(set! x (cdr x))
(set! equal #f))
((symbol=? (caar x) (caar y) (car key-lcs))
(print w indent* " (" (car key-lcs) " .\n")
(set! equal (and (diff* w (cdar x) (cdar y) (string-append indent* " "))
equal))
(print w indent* " )\n")
(set! x (cdr x))
(set! y (cdr y))
(set! key-lcs (cdr key-lcs)))
((symbol=? (caar x) (car key-lcs))
(pretty w (car y) (string-append indent* "+"))
(set! y (cdr y))
(set! equal #f))
(else
(pretty w (car x) (string-append indent* "-"))
(set! x (cdr x))
(set! equal #f)))
(loop)))
(print w indent " )\n")
equal))
((and (list? x) (list? y))
(print w indent " (\n")
(let* ((common (lcs x y equal?))
(indent* (string-append indent " "))
(equal #t))
(let loop ()
(unless (and (null? common)
(null? x)
(null? y))
(cond
((and (null? common)
(null? x))
(pretty w (car y) (string-append indent* "+"))
(set! y (cdr y))
(set! equal #f))
((and (null? common)
(null? y))
(pretty w (car x) (string-append indent* "-"))
(set! x (cdr x))
(set! equal #f))
((null? common)
(diff* w (car x) (car y) indent*)
(set! x (cdr x))
(set! y (cdr y))
(set! equal #f))
((equal? (car x) (car y))
(pretty w (car x) (string-append indent* " "))
(set! x (cdr x))
(set! y (cdr y))
(set! common (cdr common)))
((equal? (car x) (car common))
(pretty w (car y) (string-append indent* "+"))
(set! y (cdr y))
(set! equal #f))
((equal? (car y) (car common))
(pretty w (car x) (string-append indent* "-"))
(set! x (cdr x))
(set! equal #f))
(else
(diff* w (car x) (car y) indent*)
(set! x (cdr x))
(set! y (cdr y))
(set! equal #f)))
(loop)))
(print w indent " )\n")
equal))
(else
(pretty w x (string-append indent "-"))
(pretty w y (string-append indent "+"))
#f)))
(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 (let loop ((i 0)
(acc '()))
(when (< i (bytevector-length b))
(loop (+ 1 i)
(cons (string-append "0x" (number->string
(bytevector-u8-ref b i)
16))
acc)))
(reverse acc))))))))
; 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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