".el" is the convention for filename ending with Emacs Lisp programs. What is the convention when writing Common Lisp programs, please?
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Wikipedia and the Google Common Lisp Style guide both suggest .lisp
.
Practical Common Lisp suggests .lisp
or .cl
.
Note, I'm not a Common Lisp programmer by any measure, so I have no idea if .lisp
is actually used in practice.

Matt Ball
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8I just checked my Quicklisp installation that has a lot of the packages downloaded. There are a few `.cl` files (mostly related to closer-mop). The rest are `.lisp` – Elias Mårtenson Mar 03 '13 at 16:01
38
Common Lisp pathname types for source code:
lisp
is the default. Use this if possible.lsp
if the pathname type allows only three charactersl
if the pathname type should be one character (rare).
The pathname type cl
is mostly not used. You can see it sometimes in older code or projects which use several different Lisp dialects.
For compiled code the pathname type can be computed in Common Lisp using the function COMPILE-FILE-PATHNAME
(here 64bit LispWorks on a Mac):
CL-USER > (pathname-type (compile-file-pathname "foo.lisp"))
"64xfasl"

Rainer Joswig
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