[Chicken-users] [ANN] ck-macros egg

[John Croisant]

I have created a new egg, ck-macros. If you have ever written a 
syntax-rules macro and wished that you could expand its arguments ahead 
of time, this egg may be of interest to you.

The egg includes Oleg Kiselyov's "ck" macro, plus about 80 small 
composable CK-macros written by me, most of them analogous to functions 
from R5RS, SRFI-1, and SRFI-43.

For those not aware (as I wasn't until a week ago), CK-macros are a 
style of macros which use the CK abstract machine (implemented as the 
core "ck" macro) to recursively expand the CK-macro's arguments, before 
the CK-macro itself is expanded. This gives you more control over the 
macro expansion process, allowing you to easily combine simple reusable 
macros to form more complex macros. This makes it easy to write portable 
macros that previously were only feasible using non-portable features 
like CHICKEN's low level macros.

Writing CK-macros is remarkably similar to writing Scheme functions, 
except they are computed at macro-expansion time, and you have the 
benefit of syntax-rules pattern matching and destructuring. You can even 
implement "higher-ordered macros" which take a macro as an argument. For 
example the "c-map" macro applies a macro to every item in a list, at 
macro-expansion time.

Another nice thing about CK-macros is that all of the macros currently 
in the egg are implemented using only standard R5RS features, namely 
syntax-rules and let-syntax. This means they are trivially portable to 
any R5RS implementation, unlike CHICKEN's low level macros.

For more information about CK-macros, including a tutorial about how to 
write them (it's not hard, but there are a few things you must be 
careful of), see the egg wiki page: 
http://wiki.call-cc.org/eggref/4/ck-macros

In the future, I plan to add non-portable CK-macros (based on CHICKEN's 
low level macros) for string manipulation and decimal math.

Many thanks to Oleg Kiselyov for creating the "ck" macro, without which 
this egg would not be possible. Thanks also to "please_help", who 
mentioned CK-macros on IRC, which led me to learn about them.

- John Croisant