1. Cosmetic style

C:

indent-tabs-mode: nil
fill-column: 79
c-basic-offset: 4
substatement-open: 0
c-backslash-column: 77

Scheme:

(put 'and-let* 'scheme-indent-function 1)
(put 'receive 'scheme-indent-function 2)
(put 'with-exception-handler 'scheme-indent-function 1)
(put 'guard 'scheme-indent-function 1)

The value 77 for c-backslash-column is selected to maximize writable space, eliminate jagged end of lines and prevent overflow of lines on diffs posted to the uim-commit list.

Avoid placing a character at column 80 even if your editor displays it without overflow in 80-column window. Many editor displays it as continuance mark or folding mark. i.e. Treat column 79 as end-of-line, especially for decorations for comments.

2. Macro definition

Any argument should be wrapped into () or [] if no exceptional reason exist, to prevent unintended operator associations.

#define SCM_CONS_SET_CAR(a, car)   (SCM_CAR(a) = (car))

And ultra-cowardively, passing an argument to another function or macro is should also be wrapped as follows.

#define SCM_CONS(kar, kdr) (Scm_NewCons((kar), (kdr)))

This is intended to ensure unconditional safety against rare-cases such as follows.

#define FOO assert(), get_foo()
#define MAKE_LIST2(x, y) make_list(x, y)

MAKE_LIST2(FOO, SCM_FALSE);
/* => make_list(assert(), get_foo(), SCM_FALSE) */

3. Macro invocation

Don’t pass a destructive or side-effective expression to a SigScheme macro as an argument (e.g. CONTINUATIONP(continuation_stack_unwind(cont))), because there’s an possibility that continuation_stack_unwind() is evaluated multiple times after the macro expantion.