;; 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.

;; Example: pattern matches string "fodder", with (o+) matching "o"
;; and (\S+) matching "dder".  Replacement string says to replace the
;; entire match "fodder" with $2, the string matched by the second
;; parenthesized group, "dder", followed by $1, "o".
user=> (str/replace-first "fabulous fodder foo food" #"f(o+)(\S+)" "$2$1")
"fabulous ddero foo food"

;; To avoid this special treatment of $ and \, you must escape them with
;; \.  Because it is in a Clojure string, to get one \ we must escape
;; *that* with its own \.
user=> (str/replace-first "fabulous fodder foo food" #"f(o+)(\S+)" "\\$2\\$1")
"fabulous $2$1 foo food"

;; To ensure the replacement is treated literally, call
;; java.util.regex.Matcher/quoteReplacement on it.  A shorter name
;; like re-qr can be handy.
user=> (import '(java.util.regex Matcher))
java.util.regex.Matcher

user=> (defn re-qr [replacement]
         (Matcher/quoteReplacement replacement))
#'user/re-qr

user=> (str/replace-first "fabulous fodder foo food" #"f(o+)(\S+)" (re-qr "$2$1"))
"fabulous $2$1 foo food"

;; Note: When replace-first or replace have a regex pattern as their
;; match argument, dollar sign ($) and backslash (\) characters are
;; treated specially.

;; Example: pattern matches string "fodder", with (o+) matching "o"
;; and (\S+) matching "dder".  Replacement string says to replace the
;; entire match "fodder" with $2, the string matched by the second
;; parenthesized group, "dder", followed by $1, "o".
user=> (str/replace-first "fabulous fodder foo food" #"f(o+)(\S+)" "$2$1")
"fabulous ddero foo food"

;; To avoid this special treatment of $ and \, you must escape them by
;; escaping them with \.  Because it is in a Clojure string, to get
;; one \ we must escape *that* with its own \.
user=> (str/replace-first "fabulous fodder foo food" #"f(o+)(\S+)" "\\$2\\$1")
"fabulous $2$1 foo food"

;; To ensure the replacement is treated literally, call
;; java.util.regex.Matcher/quoteReplacement on it.  A shorter name
;; like re-qr can be handy.
user=> (import '(java.util.regex Matcher))
java.util.regex.Matcher

user=> (defn re-qr [replacement]
         (Matcher/quoteReplacement replacement))
#'user/re-qr

user=> (str/replace-first "fabulous fodder foo food" #"f(o+)(\S+)" (re-qr "$2$1"))
"fabulous $2$1 foo food"