3 files changed, 35 insertions(+), 13 deletions(-)

M fs/doc/lib/meta.txt
M fs/sys/file.fs
M fs/xcomp/bootlo.fs

@@ 40,13 40,7 @@ forget ( "name" -- )
   In other words, make the system forget everything that happened since "name"
   was defined.
 
-  WARNING: not all "forget" operations are clean. In fact, many "forget"
-  operations are unclean. Use with care. For example, context switching (see
-  lib/context) and forgetting don't go well together. Arena memory allocation
-  (see lib/alloc) and forgetting don't go well together.
-
-  The forget operation is useful in many situations, but be aware of its effects
-  when you use it.
+  WARNING: not all "forget" operations are clean. See section below.
 
 Words related to metadata's linked list:
 


@@ 63,3 57,30 @@ findmeta ( typeid meta -- meta-or-0 )
 .doc ( word -- )
   Print the docstring metadata associated with "word".
 
+## Forgetting is tricky
+
+The forget operation is useful in many situations, but be aware of its effects
+when you use it!
+
+Not all "forget" operations are clean. In fact, many "forget" operations are
+unclean. Use with care. For example, context switching (see lib/context) and
+forgetting don't go well together. Arena memory allocation (see lib/alloc) and
+forgetting don't go well together.
+
+Another tricky example is "floaded,", the mechanism for remembering which files
+were loaded or not, what makes ?f<< work. This is a LL where new elements are
+written to "here". When you forget past the latest "floaded" point, you break
+the whole chain, leading to memory corruption.
+
+However, it's a common pattern, when working on a file, to load it, try it, then
+forget it, then load it again and so on. This will work, but be aware of these
+facts:
+
+1. The "floaded" node is written to "here" *before* the file is actually loaded.
+2. "f<<" does not add a node if the node is already present.
+
+Therefore, you can have a "f<< / forget" loop if you always load the same single
+file. If you really need to load multiple files, you'll need to "pre-mark" your
+files as loaded with something like 'p" /my/path" Path id floaded,' and then
+individually load your files with "f<<" (implicit "?f<<" won't load anything).
+Your loaded files will then be "forget-safe".

@@ 79,10 79,7 @@ struct[ Path
   : :find# ( str -- path )
     :find ?dup not if abort" path not found" then ;
 
-  : :floaded? ( self -- f )
-    id floaded begin ( id ll )
-    ?dup while 2dup CELLSZ + @ = not while llnext repeat
-    2drop 1 else drop 0 then ;
+  : :floaded? ( self -- f ) id floaded? ;
   : :chdir ( self -- )
     dup id _curpath CELLSZ + !  fs _curpath ! ;
   : :fload ( self -- ) dup fs swap id fload ;

@@ 332,8 332,12 @@ extends IO struct[ File
 
 \ File loading
 \ TODO: support loading from multiple FSes.
-create floaded 0 , \ address of the current "loaded file" structure
-: floaded, ( id -- ) floaded lladd drop ( id ) , ;
+create floaded 0 , \ loaded files LL, *no data*
+: floaded? ( id -- f )
+  floaded begin ( id ll )
+    llnext ?dup while 2dup CELLSZ + @ = not while repeat
+    2drop 1 else drop 0 then ;
+: floaded, ( id -- ) dup floaded? if drop else floaded lladd drop , then ;
 : \s console readio IO :close ;
 : fload ( fs id -- )
   dup floaded, swap Filesystem :open ( hdl )