scexp - Symbolic C Expressions

scexp is a translator for a s-expression based syntax tree for a subset of C. It is designed to facilitate compiler writing; however, it may also be useful for those seeking a way to write low-level C code with lisp macros.

scexp depends on the common-idioms package.

The current release of scexp is 0.9, released Saturday Jan 15 2005. The release is available at the following URL:

http://www.unmutual.info/software/scexp/scexp-0.9.tar.gz

The development version is currently available as a Subversion repository at the following url:

svn://unmutual.info/scexp/

You can also browse the documentation for the latest release.

This is an example of a macro in scexp for constructing Duff's Device:

[(defmacro {make-duff} {(to from count n-type size)}
	   `{(let ((,n-type n (/ (+ ,count ,[(- {size} 1)]) ,size)))
	       (switch (mod ,count ,size)
		       (case 0)
		       (do/while
			((setq (deref ,to) (deref (post-incf ,from)))
			 ,@[(loop for i from (- {size} 1) downto 1
			       append `{((case ,[i])
					 (setq (deref ,to) (deref (post-incf ,from))))})])
			(> (decf n) 0))))})]

Which generates Duff's Device for loop unrolling in C, with a parameter of 8. Note the loop in the macro!

The funny [ and { macros switch readtables from and to the scexp readtable, which preserves case in symbols and backslashes in strings. If this looks ugly, come up with a better solution and email it to me.

To use the macro, simply call it as if it were a function:

(defun void duff8 (((* char) to) ((* char) from) (int count))
       ()
       (make-duff to from count int 8))

Last Edited: Sat Jan 15 16:00:57 CST 2005