I often have to make several substitution of the same string:
(format "%s %s %s" "a" "a" "a") ;; gives: "a a a" (it's just a dummy example, in this case it's better to glue "a" with a whitespace, but in general I deal with more complicated situations)
Is there a way to make a named substitution? For example in python one would write:
"{0} {0} {0}".format("a") # or: "{name} {name} {name}".format(name="a") Re-writing this answer gives another solution:
(format-spec "%a %a %a %b %b %b" (format-spec-make ?a "a" ?b "b")) Edit: Another format-spec solution:
As Malabarba gives another solution in comments:
(format-spec "%a %a %a %b %b %b" '((?a . "a") (?b . "b"))) Edit 2: Evaluation before substitution:
Here are examples with evaluation before substitution:
(let ((a 1) (b 2)) (format-spec "a = %a; b = %b" (format-spec-make ?a a ?b b))) ;; ⇒ "a = 1; b = 2" (let ((a 1) (b 2)) (format-spec "a = %a; b = %b" `((?a . ,a) (?b . ,b)))) ;; ⇒ "a = 1; b = 2" 
format-spec-make is just an alist: '((?a . "a") (?b . "b")) Magnar Sveen's string manipulation library s.el provides a variety of ways to do this. For example:
(require 's) (s-format "${name} ${name} ${name}" 'aget '(("name" . "test"))) ;; ==> "test test test" Note that s-format can take any replacer function, but provides special handling for aget, elt, and gethash. So you could use a list of tokens and reference them by index, like so:
(s-format "$0 $0 $0 $1 $1 $1" 'elt '("a" "b")) ;; ==> "a a a b b b" You can also replace using in-scope variables, like this:
(let ((name "test")) (s-lex-format "${name} ${name} ${name}")) ;; ==> "test test test" Since search engines lead me to this page...
Reading format documentation, I find the following:
A %-sequence other than %% may contain optional field number, flag, width, and precision specifiers, as follows: %<field><flags><width><precision>character where field is [0-9]+ followed by a literal dollar "$", flags is [+ #0-]+, width is [0-9]+, and precision is a literal period "." followed by `[0-9]+`. If a %-sequence is numbered with a field with positive value N, the Nth argument is substituted instead of the next one. A format can contain either numbered or unnumbered %-sequences but not both, except that %% can be mixed with numbered %-sequences. Which means the following will work (well.. it works for me, on Emacs 27.1)
(format "%1$s %1$s %1$s" "a") ;; gives: "a a a" 
format function (sometimes you can't control the arguments passed, only the format string itself) Not a general-purpose, but will solve your case:
(apply 'format "%s %s %s" (make-list 3 'a)) Using provided example:
(apply 'format (concat " * - :raw-html:`<img width=\"100%%\" " "src=\"http://xxx.xxx/images/languages/" "staff/%s.jpg\" alt=\"%s.jpg\"/>` - .. _%s:") (make-list 3 'some-image)) gives:
" * - :raw-html:`<img width=\"100%\" src=\"http://xxx.xxx/images/languages/staff/some-image.jpg\" alt=\"some-image.jpg\"/>` - .. _some-image:" 
" * - :raw-html:`<img width=\"100%%\" src=\"http://xxx.xxx/images/languages/staff/%s.jpg\" alt=\"%s.jpg\"/>` - .. _%s:" -- all %s are the same. s.el's s-lex-format is really what you want, but if you want to actually be able to put code inside the substitution blocks and not just variable names, I wrote this as a proof of concept.
(defmacro fmt (str) "Elisp string interpolation for any expression." (let ((exprs nil)) (with-temp-buffer (insert str) (goto-char 1) (while (re-search-forward "#{" nil t 1) (let ((here (point)) (emptyp (eql (char-after) ?}))) (unless emptyp (push (read (buffer-substring (point) (progn (forward-sexp 1) (point)))) exprs)) (delete-region (- here 2) (progn (search-forward "}") (point))) (unless emptyp (insert "%s")) (ignore-errors (forward-char 1)))) (append (list 'format (buffer-string)) (reverse exprs))))) ;; demo with variable and code substitution (fmt "My name is #{user-full-name}, I am running Emacs #{(if (display-graphic-p) \"with a GUI\" \"in a terminal\")}.") ;; results in "My name is Jordon Biondo, I am running Emacs with a GUI." You can even embed an fmt call inside another fmt if you're crazy
(fmt "#{(fmt\"#{(fmt\\\"#{user-full-name}\\\")}\")}") ;; => "Jordon Biondo" The code just expands to a format call so all the substitutions are done in order and evaluated at run time.
(cl-prettyexpand '(fmt "Hello, I'm running Emacs #{emacs-version} on a #{system-type} machine with #{(length (window-list))} open windows.")) ;; expands to (format "Hello, I'm running Emacs %s on a %s machine with %s open windows." emacs-version system-type (length (window-list))) Improvements could be made with what format type is used instead of always using %s, but that would have to be done at runtime and would add overhead but could be done by surrounding all the format args in a function call that nicely formats things nicely based on type but really the only scenario where you would want that is probably floats and you could even do a (format "%f" float) in the substitution is you were desperate.
If I work on it more, I'm more likely to update this gist instead of this answer. https://gist.github.com/jordonbiondo/c4e22b4289be130bc59b
