String prepend: Difference between revisions

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 =={{header|Emacs Lisp}}==
-===version 1===
+While strings in Emacs Lisp are mutable, they're fixed size. Therefore the <code>concat</code> function creates a new string and the existing string must be referenced twice:
-<lang Emacs Lisp>
-(defun glue (str1 str2)
+<lang Lisp>(defvar str "bar")
-  (concat str1 str2) )
+(setq str (concat "foo" str))
-</lang>
+str ;=> "foobar"</lang>
-===version 2===
-<lang Emacs Lisp>
+This can be hidden by using a macro such as <code>cl-callf2</code> which expands into the above code:
-(defun glue (str1 str2)
-  (format "%s%s" str1 str2) )
+{{libheader|cl-lib}}
-</lang>
+<lang Lisp>(require 'cl-lib)
-<b>Eval:</b>
-<lang Emacs Lisp>
-(setq str "World!")
+(defvar str "bar")
-(setq str (glue "Hello, " str) )
+(cl-callf2 concat "foo" str)
+str ;=> "foobar"</lang>
-(insert str)
-</lang>
+Buffers can be thought of as expandable strings:
-<b>Output:</b>
-<pre>
+<lang Lisp>(let ((buf (get-buffer-create "*foo*")))
-Hello, World!
+  (with-current-buffer buf
-</pre>
+    (insert "bar"))
+  (with-current-buffer buf
+    (goto-char (point-min))
+    (insert "foo")
+    (buffer-string)))
+;; => "foobar"</lang>
 =={{header|Erlang}}==