Merge branch 'master' into call-cc

diff --cc src/scheme.4th
index e94796c,2a509e6..93d2496
--- 1/src/scheme.4th
--- 2/src/scheme.4th
+++ b/src/scheme.4th
@@@ -2006,6 -1939,29 +2000,21 @@@ parse-idx-stack parse-idx-sp 
  
  \ ---- Garbage Collection ---- {{{
  
 -variable gc-stack-depth
 -
 -: enable-gc
 -    depth gc-stack-depth !
 -    true gc-enabled ! ;
 -
 -: disable-gc
 -    false gc-enabled ! ;
+ ( Notes on garbage collection:
+   This is a mark-sweep garbage collector, invoked by cons.
+   The roots of the object tree used by the marking routine 
+   include all objects in the parameter stack, and several
+   other fixed roots such as global-env, symbol-table, macro-table,
+   and the console-i/o-port.
+ 
+   NO OTHER OBJECTS WILL BE MARKED!
+ 
+   This places implicit restrictions on when cons can be invoked.
+   Invoking cons when live objects are stored on the return stack
+   or in other variables than the above will result in possible
+   memory corruption if the cons triggers the GC. )
+ 
+ 
  : pairlike? ( obj -- obj bool )
      pair-type istype? if true exit then
      string-type istype? if true exit then