i think I found a bug in clojure, can anyone explain why the backslash is missing from the output?
(clojure.string/replace "The color? is red." #"[?.]" #(str "zzz\\j" %1 %1))
=> "The colorzzzj?? is redzzzj.."
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2 Answers
This isn't a bug. The string returned by the function in the 3rd parameter is parsed for escape sequences so that you can do things like this:
(clojure.string/replace "The color? is red." #"([?.])" "\\$1$1")
; => "The color$1? is red$1."
Notice how the first $ is escaped by the backslash, whereas the second serves as the identifier for a capture group. Change your code to use four backslashes and it works:
(clojure.string/replace "The color? is red." #"[?.]" #(str "zzz\\\\j" %1 %1))
2 Comments
DaoWen
Matt Ball - Actually, it only results in a single backslash—but I can see why you'd get confused. When you run the command in the REPL it prints the result as a string literal, in which case it has to show the single backslash as escaped since it's inside the string literal. Try wrapping the whole thing in a
println call and you'll see that the result really one has one backslash.DaoWen
Matt Ball - Ah, sorry, I didn't actually look at the code you posted. The same principle applies though. The
pr function prints data in a way that the reader can parse, whereas print outputs data in a human-readable format. Since the data is a string in this case, pr prints a string literal (notice the surrounding quotes), whereas print just outputs the raw string of characters to the console. Change your pr to a print and you'll get the expected output.Please check the function documentation at: http://clojuredocs.org/clojure_core/clojure.string/replace
Specifically:
Note: When replace-first or replace have a regex pattern as their match argument, dollar sign ($) and backslash (\) characters in the replacement string are treated specially.
