I think the docs are just worded a little bit carefully. From what I can tell, it is the identity function on pairs (and on anything that isn't explicitly listed in the docs, actually).
But one note: in the common case, it looks like your code will copy all of the strings: > (define x "abc") > (substring x 0) "abc" > (eq? x (substring x 0)) #f I guess these strings are not mutated, so you can probably avoid that in the start = 0 case (something I see the original code does). Robby On Monday, June 25, 2012, Danny Yoo wrote: > Hi everyone, > > Is there a reason to use the function "datum-intern-literal" on a list > structure? According to the documentation, datum-intern-literal does > not traverse compound values, so I'm unsure about its use on list > structures. > > I'm curious because I'm staring at the definition of decode-string in > scribble/decode, and it's trying to apply datum-intern-literal against > a whole list, which seems strange to me: > > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; > (define (decode-string s) > (let loop ([l '((#rx"---" mdash) > (#rx"--" ndash) > (#rx"``" ldquo) > (#rx"''" rdquo) > (#rx"'" rsquo))]) > (cond [(null? l) (list s)] > [(regexp-match-positions (caar l) s) > => (lambda (m) > (datum-intern-literal > (append (decode-string (substring s 0 (caar m))) > (cdar l) > (decode-string (substring s (cdar m))))))] > [else (loop (cdr l))]))) > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; > > > I'm looking at this function because the Racket statistical profiler > is telling me that it might be helpful to optimize it. I had expected > something more along the lines of: > > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; > (define (decode-string s) > (define pattern #rx"(---|--|``|''|')") > (let loop ([start 0]) > (cond > [(regexp-match-positions pattern s start) > => (lambda (m) > (define the-match (substring s (caar m) (cdar m))) > (list* (substring s start (caar m)) > (cond > [(string=? the-match "---") 'mdash] > [(string=? the-match "--") 'ndash] > [(string=? the-match "``") 'ldquo] > [(string=? the-match "''") 'rdquo] > [(string=? the-match "'") 'rsquo]) > (loop (cdar m))))] > [else > (list (substring s start))]))) > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; > > but I'm not sure about the role of the datum-intern-literal stuff with > regards to lists. > ____________________ > Racket Users list: > http://lists.racket-lang.org/users >
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