CL-INTERPOL modifies the reader so that you can have interpolation of strings similar to Perl or Unix Shell scripts. It is a text processing convenience library. It also provides various ways to insert arbitrary characters into literal strings even if your editor/IDE doesn't support them.

Here's an example:

* (let ((a 42))
    #?"foo: \xC4\N{Latin capital letter U with diaeresis}\nbar: ${a}")
"foo: ÄÜ
bar: 42"

It was written by Edi Weitz and now maintained by community at Github.

CL-INTERPOL can also be used for HTML templating: