resolve merge

[lilypond.git] / scm / lily-sort.scm

diff --git a/scm/lily-sort.scm b/scm/lily-sort.scm
new file mode 100644 (file)
index 0000000..ac239a7
--- /dev/null
+++ b/scm/lily-sort.scm
@@ -0,0 +1,116 @@
+;;;; lily-sort.scm -- improved sorting of symbols, strings, and alists.
+;;;;
+;;;; source file of the GNU LilyPond music typesetter
+;;;;
+;;;; Copyright 2009--2011 Mark Polesky <markpolesky@yahoo.com>
+
+
+;; This file implements a LilyPond-specific character-sorting algorithm
+;; that can be used to sort lists, alists, etc. consistently and
+;; predictably throughout the source code. The primary advantage of this
+;; algorithm is that lists are sorted in a more intuitive way, which may
+;; allow users to find items faster in the documentation.
+;;
+;; As an example, a user, looking in the documentation to see if there's
+;; a function called "ly:grob?", might assume that there isn't one,
+;; since it doesn't appear before "ly:grob-alist-chain" (using the
+;; default sort).
+;;
+;; This happens because "-" comes before "?" in the default sort order.
+;; But since "?" is more likely to come at the end of a scheme symbol, a
+;; more intuitive sort can be achieved by reversing that order.
+;;
+;; Similarly, non-alphanumeric characters can be ranked in terms of how
+;; likely one will be found closer to the end of a symbol. For example,
+;; ":" is stronger separator than "-", as can be seen here:
+;;
+;; "ly:staff-symbol::print"
+;; "ly:staff-symbol-referencer::callback"
+;;
+;; Intuitively, "staff-symbol-referencer" ought to come after
+;; "staff-symbol", but since "-" comes before ":" in the default sort
+;; order, these symbols are by default listed in the opposite order.
+;;
+;; Thus the algorithm implemented here ranks the following nine
+;; characters (starting with the space character) in order from
+;; most-to-least likely to terminate a symbol: " !?<=>:-_". These nine
+;; characters are in effect "extracted" from the default order and then
+;; "prepended" to it so that they now come first. This is achieved with
+;; the function "ly:char-generic-<?".
+;;
+;; This file defines 3 case-sensitive binary comparison predicates:
+;;   ly:string<?     ly:symbol<?     ly:alist<?
+;; and their case-insensitive counterparts:
+;;   ly:string-ci<?  ly:symbol-ci<?  ly:alist-ci<?
+;;
+;; Case-insensitive predicates are recommended in general; otherwise
+;; symbols like "Y-offset" appear near the top of lists which
+;; otherwise include mostly lowercase symbols.
+
+(define (ly:char-generic-<? a b ci)
+  (let* ((init-list (string->list " !?<=>:-_"))
+         (mem-a (member a init-list))
+         (mem-b (member b init-list)))
+    (cond ((and mem-a mem-b) (< (length mem-b) (length mem-a)))
+          (mem-a #t)
+          (mem-b #f)
+          (else ((if ci char-ci<? char<?) a b)))))
+
+(define (ly:char<? a b)
+  (ly:char-generic-<? a b #f))
+
+(define (ly:char-ci<? a b)
+  (ly:char-generic-<? a b #t))
+
+(define (first-diff-chars str0 str1 ci)
+  (let find-mismatch ((a (string->list str0)) (b (string->list str1)))
+    (cond ((and (null? a) (null? b)) #f)
+          ((null? a) (cons #f (car b)))
+          ((null? b) (cons (car a) #f))
+          ((not ((if ci char-ci=? char=?) (car a) (car b)))
+              (cons (car a) (car b)))
+          (else (find-mismatch (cdr a) (cdr b))))))
+
+(define (ly:string-generic-<? a b ci)
+  (let ((mismatch (first-diff-chars a b ci)))
+    (cond ((and mismatch (car mismatch) (cdr mismatch))
+             ((if ci ly:char-ci<? ly:char<?)
+                   (car mismatch) (cdr mismatch)))
+          ((and mismatch (cdr mismatch)) #t)
+          (else #f))))
+
+(define (ly:string<? a b)
+  "Return #t if string A is less than string B in case-sensitive
+  LilyPond sort order."
+  (ly:string-generic-<? a b #f))
+
+(define (ly:string-ci<? a b)
+  "Return #t if string A is less than string B in case-insensitive
+  LilyPond sort order."
+  (ly:string-generic-<? a b #t))
+
+(define (ly:symbol<? a b)
+  "Return #t if symbol A is less than symbol B in case-sensitive
+  LilyPond sort order."
+  (ly:string<? (symbol->string a)
+               (symbol->string b)))
+
+(define (ly:symbol-ci<? a b)
+  "Return #t if symbol A is less than symbol B in case-insensitive
+  LilyPond sort order."
+  (ly:string-ci<? (symbol->string a)
+                  (symbol->string b)))
+
+(define (ly:alist<? a b)
+  "Return #t if the first key of alist A is less than the first key of
+  alist B, using case-sensitive LilyPond sort order.  Keys are assumed to
+  be symbols."
+  (ly:string<? (symbol->string (car a))
+               (symbol->string (car b))))
+
+(define (ly:alist-ci<? a b)
+  "Return #t if the first key of alist A is less than the first key of
+  alist B, using case-insensitive LilyPond sort order.  Keys are assumed
+  to be symbols."
+  (ly:string-ci<? (symbol->string (car a))
+                  (symbol->string (car b))))