diff --git a/src/Make_ming.mak b/src/Make_ming.mak
index 6d28e46..e0717b6 100644
--- a/src/Make_ming.mak
+++ b/src/Make_ming.mak
@@ -115,8 +115,21 @@
 MZSCHEME_VER=205_000
 endif
 
+ifndef MZSCHEME_PRECISE_GC
+MZSCHEME_PRECISE_GC=no
+endif
+
+# for version 4.x we need to generate byte-code for Scheme base
+ifndef MZSCHEME_GENERATE_BASE
+MZSCHEME_GENERATE_BASE=no
+endif
+
 ifeq (no,$(DYNAMIC_MZSCHEME))
+ifeq (yes,$(MZSCHEME_PRECISE_GC))
+MZSCHEME_LIB=-lmzsch$(MZSCHEME_VER)
+else
 MZSCHEME_LIB = -lmzsch$(MZSCHEME_VER) -lmzgc$(MZSCHEME_VER)
+endif
 # the modern MinGW can dynamically link to dlls directly.
 # point MZSCHEME_DLLS to where you put libmzschXXXXXXX.dll and libgcXXXXXXX.dll
 ifndef MZSCHEME_DLLS
@@ -410,6 +423,13 @@
 ifdef MZSCHEME
 OBJ += $(OUTDIR)/if_mzsch.o
 MZSCHEME_INCL = if_mzsch.h
+ifeq (yes,$(MZSCHEME_GENERATE_BASE))
+CFLAGS += -DINCLUDE_MZSCHEME_BASE
+MZ_EXTRA_DEP += mzscheme_base.c
+endif
+ifeq (yes,$(MZSCHEME_PRECISE_GC))
+CFLAGS += -DMZ_PRECISE_GC
+endif
 endif
 ifdef PYTHON
 OBJ += $(OUTDIR)/if_python.o
@@ -588,6 +608,12 @@
 $(OUTDIR)/netbeans.o:	netbeans.c $(INCL) $(NBDEBUG_INCL) $(NBDEBUG_SRC)
 	$(CC) -c $(CFLAGS) netbeans.c -o $(OUTDIR)/netbeans.o
 
+$(OUTDIR)/if_mzsch.o:	if_mzsch.c $(INCL) if_mzsch.h $(MZ_EXTRA_DEP)
+	$(CC) -c $(CFLAGS) if_mzsch.c -o $(OUTDIR)/if_mzsch.o
+
+mzscheme_base.c:
+	$(MZSCHEME)/mzc --c-mods mzscheme_base.c ++lib scheme/base
+
 pathdef.c: $(INCL)
 ifneq (sh.exe, $(SHELL))
 	@echo creating pathdef.c
diff --git a/src/Make_mvc.mak b/src/Make_mvc.mak
index 545c94d..1782586 100644
--- a/src/Make_mvc.mak
+++ b/src/Make_mvc.mak
@@ -34,6 +34,7 @@
 #	  MZSCHEME=[Path to MzScheme directory]
 #	  DYNAMIC_MZSCHEME=yes (to load the MzScheme DLLs dynamically)
 #	  MZSCHEME_VER=[version, 205_000, ...]
+#	  MZSCHEME_DEBUG=no
 #
 #	Perl interface:
 #	  PERL=[Path to Perl directory]
@@ -621,15 +622,37 @@
 MZSCHEME_VER = 205_000
 !endif
 CFLAGS = $(CFLAGS) -DFEAT_MZSCHEME -I $(MZSCHEME)\include
+!if EXIST("$(MZSCHEME)\collects\scheme\base.ss")
+# for MzScheme 4.x we need to include byte code for basic Scheme stuff
+MZSCHEME_EXTRA_DEP = mzscheme_base.c
+CFLAGS = $(CFLAGS) -DINCLUDE_MZSCHEME_BASE
+!endif
+!if EXIST("$(MZSCHEME)\lib\msvc\libmzsch$(MZSCHEME_VER).lib") \
+	&& !EXIST("$(MZSCHEME)\lib\msvc\libmzgc$(MZSCHEME_VER).lib")
+!message Building with Precise GC
+MZSCHEME_PRECISE_GC = yes
+CFLAGS = $(CFLAGS) -DMZ_PRECISE_GC
+!endif
 !if "$(DYNAMIC_MZSCHEME)" == "yes"
+!if "$(MZSCHEME_PRECISE_GC)" == "yes"
+!error MzScheme with Precise GC cannot be loaded dynamically
+!endif
 !message MzScheme DLLs will be loaded dynamically
 CFLAGS = $(CFLAGS) -DDYNAMIC_MZSCHEME \
 		-DDYNAMIC_MZSCH_DLL=\"libmzsch$(MZSCHEME_VER).dll\" \
 		-DDYNAMIC_MZGC_DLL=\"libmzgc$(MZSCHEME_VER).dll\"
 !else
+!if "$(MZSCHEME_DEBUG)" == "yes"
+CFLAGS = $(CFLAGS) -DMZSCHEME_FORCE_GC
+!endif
+!if "$(MZSCHEME_PRECISE_GC)" == "yes"
+# Precise GC does not use separate dll
+MZSCHEME_LIB = $(MZSCHEME)\lib\msvc\libmzsch$(MZSCHEME_VER).lib
+!else
 MZSCHEME_LIB = $(MZSCHEME)\lib\msvc\libmzgc$(MZSCHEME_VER).lib \
 		$(MZSCHEME)\lib\msvc\libmzsch$(MZSCHEME_VER).lib
 !endif
+!endif
 MZSCHEME_OBJ = $(OUTDIR)\if_mzsch.obj
 !endif
 
@@ -930,9 +953,11 @@
 $(OUTDIR)/if_perlsfio.obj: $(OUTDIR) if_perlsfio.c  $(INCL)
 	$(CC) $(CFLAGS) $(PERL_INC) if_perlsfio.c
 
-$(OUTDIR)/if_mzsch.obj: $(OUTDIR) if_mzsch.c  $(INCL)
+$(OUTDIR)/if_mzsch.obj: $(OUTDIR) if_mzsch.c  $(INCL) $(MZSCHEME_EXTRA_DEP)
 	$(CC) $(CFLAGS) if_mzsch.c \
 		-DMZSCHEME_COLLECTS=\"$(MZSCHEME:\=\\)\\collects\"
+mzscheme_base.c:
+	$(MZSCHEME)\mzc --c-mods mzscheme_base.c ++lib scheme/base
 
 $(OUTDIR)/if_python.obj: $(OUTDIR) if_python.c  $(INCL)
 	$(CC) $(CFLAGS) $(PYTHON_INC) if_python.c
diff --git a/src/Makefile b/src/Makefile
index e6d26b1..02b8d6c 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -536,7 +536,7 @@
 # Use this with GCC to check for mistakes, unused arguments, etc.
 #CFLAGS = -g -Wall -Wextra -Wmissing-prototypes -Wunreachable-code
 #PYTHON_CFLAGS_EXTRA = -Wno-missing-field-initializers
-#MZSCHEME_CFLAGS_EXTRA = -Wno-unreachable-code
+#MZSCHEME_CFLAGS_EXTRA = -Wno-unreachable-code -Wno-unused-parameter
 
 # EFENCE - Electric-Fence malloc debugging: catches memory accesses beyond
 # allocated memory (and makes every malloc()/free() very slow).
@@ -2200,6 +2200,7 @@
 	-rm -f $(TOOLS) auto/osdef.h auto/pathdef.c auto/if_perl.c
 	-rm -f conftest* *~ auto/link.sed
 	-rm -rf $(APPDIR)
+	-rm -rf mzscheme_base.c
 	if test -d $(PODIR); then \
 		cd $(PODIR); $(MAKE) prefix=$(DESTDIR)$(prefix) clean; \
 	fi
@@ -2433,8 +2434,11 @@
 objects/if_xcmdsrv.o: if_xcmdsrv.c
 	$(CCC) -o $@ if_xcmdsrv.c
 
-objects/if_mzsch.o: if_mzsch.c
+objects/if_mzsch.o: if_mzsch.c $(MZSCHEME_EXTRA)
 	$(CCC) -o $@ $(MZSCHEME_CFLAGS_EXTRA) if_mzsch.c
+ 
+mzscheme_base.c:
+	$(MZSCHEME_MZC) --c-mods mzscheme_base.c ++lib scheme/base
 
 objects/if_perl.o: auto/if_perl.c
 	$(CCC) -o $@ auto/if_perl.c
diff --git a/src/auto/configure b/src/auto/configure
index 596e034..42f4784 100755
--- a/src/auto/configure
+++ b/src/auto/configure
Binary files differ
diff --git a/src/config.mk.in b/src/config.mk.in
index 9590d44..f36e676 100644
--- a/src/config.mk.in
+++ b/src/config.mk.in
@@ -41,6 +41,8 @@
 MZSCHEME_OBJ	= @MZSCHEME_OBJ@
 MZSCHEME_CFLAGS	= @MZSCHEME_CFLAGS@
 MZSCHEME_PRO	= @MZSCHEME_PRO@
+MZSCHEME_EXTRA  = @MZSCHEME_EXTRA@
+MZSCHEME_MZC	= @MZSCHEME_MZC@
 
 PERL		= @vi_cv_path_perl@
 PERLLIB		= @vi_cv_perllib@
diff --git a/src/configure.in b/src/configure.in
index a644d94..eb7db76 100644
--- a/src/configure.in
+++ b/src/configure.in
@@ -414,7 +414,7 @@
 	AC_MSG_RESULT("$PLTHOME")
 	vi_cv_path_mzscheme_pfx="$PLTHOME"
     else
-	AC_MSG_RESULT("not set")
+	AC_MSG_RESULT(not set)
 	dnl -- try to find MzScheme executable
 	AC_PATH_PROG(vi_cv_path_mzscheme, mzscheme)
 
@@ -430,14 +430,16 @@
 	if test "X$vi_cv_path_mzscheme" != "X"; then
 	    dnl -- find where MzScheme thinks it was installed
 	    AC_CACHE_CHECK(MzScheme install prefix,vi_cv_path_mzscheme_pfx,
-	    [ vi_cv_path_mzscheme_pfx=`
-	    ${vi_cv_path_mzscheme} -evm \
-	    "(display (simplify-path		\
+	    dnl different versions of MzScheme differ in command line processing
+	    dnl use universal approach
+	    echo "(display (simplify-path		\
 	       (build-path (call-with-values	\
 		(lambda () (split-path (find-system-path (quote exec-file)))) \
-		(lambda (base name must-be-dir?) base)) (quote up))))"` ])
-	    dnl Remove a trailing slash.
-	    vi_cv_path_mzscheme_pfx=`echo "$vi_cv_path_mzscheme_pfx" | sed 's+/$++'`
+		(lambda (base name must-be-dir?) base)) (quote up))))" > mzdirs.scm
+	    dnl Remove a trailing slash
+	    [ vi_cv_path_mzscheme_pfx=`${vi_cv_path_mzscheme} -r mzdirs.scm | \
+		sed -e 's+/$++'` ])
+	    rm -f mzdirs.scm
 	fi
     fi
   fi
@@ -446,16 +448,24 @@
   if test "X$vi_cv_path_mzscheme_pfx" != "X"; then
     AC_MSG_CHECKING(if scheme.h can be found in $vi_cv_path_mzscheme_pfx/include)
     if test -f $vi_cv_path_mzscheme_pfx/include/scheme.h; then
-      AC_MSG_RESULT("yes")
+      SCHEME_INC=${vi_cv_path_mzscheme_pfx}/include
+      AC_MSG_RESULT(yes)
     else
-      AC_MSG_RESULT("no")
-      AC_MSG_CHECKING(if scheme.h can be found in $vi_cv_path_mzscheme_pfx/plt/include)
+      AC_MSG_RESULT(no)
+      AC_MSG_CHECKING(if scheme.h can be found in $vi_cv_path_mzscheme_pfx/include/plt)
       if test -f $vi_cv_path_mzscheme_pfx/include/plt/scheme.h; then
-	AC_MSG_RESULT("yes")
-	SCHEME_INC=/plt
+	AC_MSG_RESULT(yes)
+	SCHEME_INC=${vi_cv_path_mzscheme_pfx}/include/plt
       else
-	AC_MSG_RESULT("no")
-	vi_cv_path_mzscheme_pfx=
+	AC_MSG_RESULT(no)
+	AC_MSG_CHECKING(if scheme.h can be found in /usr/include/plt/)
+	if test -f /usr/include/plt/scheme.h; then
+	  AC_MSG_RESULT(yes)
+	  SCHEME_INC=/usr/include/plt
+	else
+	  AC_MSG_RESULT(no)
+	  vi_cv_path_mzscheme_pfx=
+	fi
       fi
     fi
   fi
@@ -463,23 +473,38 @@
   if test "X$vi_cv_path_mzscheme_pfx" != "X"; then
     if test "x$MACOSX" = "xyes"; then
       MZSCHEME_LIBS="-framework PLT_MzScheme"
+    elif test -f "${vi_cv_path_mzscheme_pfx}/lib/libmzscheme3m.a"; then
+      MZSCHEME_LIBS="${vi_cv_path_mzscheme_pfx}/lib/libmzscheme3m.a"
+      MZSCHEME_CFLAGS="-DMZ_PRECISE_GC"
     elif test -f "${vi_cv_path_mzscheme_pfx}/lib/libmzgc.a"; then
       MZSCHEME_LIBS="${vi_cv_path_mzscheme_pfx}/lib/libmzscheme.a ${vi_cv_path_mzscheme_pfx}/lib/libmzgc.a"
     else
-      MZSCHEME_LIBS="-L${vi_cv_path_mzscheme_pfx}/lib -lmzscheme -lmzgc"
+      dnl Using shared objects
+      if test -f "${vi_cv_path_mzscheme_pfx}/lib/libmzscheme3m.so"; then
+        MZSCHEME_LIBS="-L${vi_cv_path_mzscheme_pfx}/lib -lmzscheme3m"
+	MZSCHEME_CFLAGS="-DMZ_PRECISE_GC"
+      else
+        MZSCHEME_LIBS="-L${vi_cv_path_mzscheme_pfx}/lib -lmzscheme -lmzgc"
+      fi
       if test "$GCC" = yes; then
 	dnl Make Vim remember the path to the library.  For when it's not in
 	dnl $LD_LIBRARY_PATH.
-	MZSCHEME_LIBS="$MZSCHEME_LIBS -Wl,-rpath -Wl,${vi_cv_path_mzscheme_pfx}/lib"
+	MZSCHEME_LIBS="${MZSCHEME_LIBS} -Wl,-rpath -Wl,${vi_cv_path_mzscheme_pfx}/lib"
       elif test "`(uname) 2>/dev/null`" = SunOS &&
 			       uname -r | grep '^5' >/dev/null; then
-	MZSCHEME_LIBS="$MZSCHEME_LIBS -R ${vi_cv_path_mzscheme_pfx}/lib"
+	MZSCHEME_LIBS="${MZSCHEME_LIBS} -R ${vi_cv_path_mzscheme_pfx}/lib"
       fi
     fi
     if test -d $vi_cv_path_mzscheme_pfx/lib/plt/collects; then
       SCHEME_COLLECTS=lib/plt/
     fi
-    MZSCHEME_CFLAGS="-I${vi_cv_path_mzscheme_pfx}/include${SCHEME_INC}   \
+    if test -f "${vi_cv_path_mzscheme_pfx}/${SCHEME_COLLECTS}collects/scheme/base.ss" ; then
+      dnl need to generate bytecode for MzScheme base
+      MZSCHEME_EXTRA="mzscheme_base.c"
+      MZSCHEME_CFLAGS="${MZSCHEME_CFLAGS} -DINCLUDE_MZSCHEME_BASE"
+      MZSCHEME_MZC="${vi_cv_path_mzscheme_pfx}/bin/mzc"
+    fi
+    MZSCHEME_CFLAGS="${MZSCHEME_CFLAGS} -I${SCHEME_INC} \
       -DMZSCHEME_COLLECTS='\"${vi_cv_path_mzscheme_pfx}/${SCHEME_COLLECTS}collects\"'"
     MZSCHEME_SRC="if_mzsch.c"
     MZSCHEME_OBJ="objects/if_mzsch.o"
@@ -491,6 +516,8 @@
   AC_SUBST(MZSCHEME_PRO)
   AC_SUBST(MZSCHEME_LIBS)
   AC_SUBST(MZSCHEME_CFLAGS)
+  AC_SUBST(MZSCHEME_EXTRA)
+  AC_SUBST(MZSCHEME_MZC)
 fi
 
 
diff --git a/src/eval.c b/src/eval.c
index 2e3d9fd..bf0c303 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -5866,7 +5866,7 @@
     return item1 == NULL && item2 == NULL;
 }
 
-#if defined(FEAT_PYTHON) || defined(PROTO)
+#if defined(FEAT_PYTHON) || defined(FEAT_MZSCHEME) || defined(PROTO)
 /*
  * Return the dictitem that an entry in a hashtable points to.
  */
diff --git a/src/if_mzsch.c b/src/if_mzsch.c
index 7f43cab..017f804 100644
--- a/src/if_mzsch.c
+++ b/src/if_mzsch.c
@@ -4,6 +4,8 @@
  * Original work by Brent Fulgham <bfulgham@debian.org>
  * (Based on lots of help from Matthew Flatt)
  *
+ * TODO Convert byte-strings to char strings?
+ *
  * This consists of six parts:
  * 1. MzScheme interpreter main program
  * 2. Routines that handle the external interface between MzScheme and
@@ -18,7 +20,7 @@
  *    garbage collector will do it self
  * 2. Requires at least NORMAL features. I can't imagine why one may want
  *    to build with SMALL or TINY features but with MzScheme interface.
- * 3. I don't use K&R-style functions. Anyway, MzScheme headers are ANSI.
+ * 3. I don't use K&R-style functions. Anyways, MzScheme headers are ANSI.
  */
 
 #include "vim.h"
@@ -29,14 +31,15 @@
  * depend". */
 #if defined(FEAT_MZSCHEME) || defined(PROTO)
 
+#include <assert.h>
+
 /* Base data structures */
 #define SCHEME_VIMBUFFERP(obj)  SAME_TYPE(SCHEME_TYPE(obj), mz_buffer_type)
 #define SCHEME_VIMWINDOWP(obj)  SAME_TYPE(SCHEME_TYPE(obj), mz_window_type)
 
 typedef struct
 {
-    Scheme_Type	    tag;
-    Scheme_Env	    *env;
+    Scheme_Object   so;
     buf_T	    *buf;
 } vim_mz_buffer;
 
@@ -44,7 +47,7 @@
 
 typedef struct
 {
-    Scheme_Type	    tag;
+    Scheme_Object   so;
     win_T	    *win;
 } vim_mz_window;
 
@@ -67,19 +70,6 @@
     Scheme_Object   *port;
 } Port_Info;
 
-/* info for closed prim */
-/*
- * data have different means:
- * for do_eval it is char*
- * for do_apply is Apply_Onfo*
- * for do_load is Port_Info*
- */
-typedef struct
-{
-    void	*data;
-    Scheme_Env	*env;
-} Cmd_Info;
-
 /* info for do_apply */
 typedef struct
 {
@@ -122,7 +112,6 @@
 static Scheme_Object *insert_buffer_line_list(void *, int, Scheme_Object **);
 static Scheme_Object *get_range_start(void *, int, Scheme_Object **);
 static Scheme_Object *get_range_end(void *, int, Scheme_Object **);
-static Scheme_Object *get_buffer_namespace(void *, int, Scheme_Object **);
 static vim_mz_buffer *get_vim_curr_buffer(void);
 
 /*  Window-related commands */
@@ -163,8 +152,6 @@
 static int do_mzscheme_command(exarg_T *, void *, Scheme_Closed_Prim *what);
 static void startup_mzscheme(void);
 static char *string_to_line(Scheme_Object *obj);
-static int mzscheme_io_init(void);
-static void mzscheme_interface_init(vim_mz_buffer *self);
 static void do_output(char *mesg, long len);
 static void do_printf(char *format, ...);
 static void do_flush(void);
@@ -174,19 +161,52 @@
 static Scheme_Object *do_eval(void *, int noargc, Scheme_Object **noargv);
 static Scheme_Object *do_load(void *, int noargc, Scheme_Object **noargv);
 static Scheme_Object *do_apply(void *, int noargc, Scheme_Object **noargv);
-static void register_vim_exn(Scheme_Env *env);
+static void register_vim_exn(void);
 static vim_mz_buffer *get_buffer_arg(const char *fname, int argnum,
 	int argc, Scheme_Object **argv);
 static vim_mz_window *get_window_arg(const char *fname, int argnum,
 	int argc, Scheme_Object **argv);
-static void add_vim_exn(Scheme_Env *env);
 static int line_in_range(linenr_T, buf_T *);
 static void check_line_range(linenr_T, buf_T *);
 static void mz_fix_cursor(int lo, int hi, int extra);
 
-static int eval_in_namespace(void *, Scheme_Closed_Prim *, Scheme_Env *,
-		Scheme_Object **ret);
-static void make_modules(Scheme_Env *);
+static int eval_with_exn_handling(void *, Scheme_Closed_Prim *,
+	    Scheme_Object **ret);
+static void make_modules(void);
+static void init_exn_catching_apply(void);
+static int mzscheme_env_main(Scheme_Env *env, int argc, char **argv);
+static int mzscheme_init(void);
+#ifdef FEAT_EVAL
+static Scheme_Object *vim_to_mzscheme(typval_T *vim_value, int depth,
+	Scheme_Hash_Table *visited);
+#endif
+
+#ifdef MZ_PRECISE_GC
+static int buffer_size_proc(void *obj)
+{
+    return gcBYTES_TO_WORDS(sizeof(vim_mz_buffer));
+}
+static int buffer_mark_proc(void *obj)
+{
+    return buffer_size_proc(obj);
+}
+static int buffer_fixup_proc(void *obj)
+{
+    return buffer_size_proc(obj);
+}
+static int window_size_proc(void *obj)
+{
+    return gcBYTES_TO_WORDS(sizeof(vim_mz_window));
+}
+static int window_mark_proc(void *obj)
+{
+    return window_size_proc(obj);
+}
+static int window_fixup_proc(void *obj)
+{
+    return window_size_proc(obj);
+}
+#endif
 
 #ifdef DYNAMIC_MZSCHEME
 
@@ -260,8 +280,6 @@
     (Scheme_Closed_Prim *prim, void *data, const char *name, mzshort mina,
      mzshort maxa);
 static Scheme_Object *(*dll_scheme_make_integer_value)(long i);
-static Scheme_Object *(*dll_scheme_make_namespace)(int argc,
-	Scheme_Object *argv[]);
 static Scheme_Object *(*dll_scheme_make_pair)(Scheme_Object *car,
 	Scheme_Object *cdr);
 static Scheme_Object *(*dll_scheme_make_prim_w_arity)(Scheme_Prim *prim,
@@ -311,6 +329,17 @@
 static Scheme_Object *(*dll_scheme_char_string_to_path)
     (Scheme_Object *s);
 # endif
+static Scheme_Hash_Table *(*dll_scheme_make_hash_table)(int type);
+static void (*dll_scheme_hash_set)(Scheme_Hash_Table *table,
+	Scheme_Object *key, Scheme_Object *value);
+static Scheme_Object *(*dll_scheme_hash_get)(Scheme_Hash_Table *table,
+	Scheme_Object *key);
+static Scheme_Object *(*dll_scheme_make_double)(double d);
+# ifdef INCLUDE_MZSCHEME_BASE
+static Scheme_Object *(*dll_scheme_make_sized_byte_string)(char *chars,
+	long len, int copy);
+static Scheme_Object *(*dll_scheme_namespace_require)(Scheme_Object *req);
+# endif
 
 /* arrays are imported directly */
 # define scheme_eof dll_scheme_eof
@@ -368,7 +397,6 @@
 # define scheme_lookup_global dll_scheme_lookup_global
 # define scheme_make_closed_prim_w_arity dll_scheme_make_closed_prim_w_arity
 # define scheme_make_integer_value dll_scheme_make_integer_value
-# define scheme_make_namespace dll_scheme_make_namespace
 # define scheme_make_pair dll_scheme_make_pair
 # define scheme_make_prim_w_arity dll_scheme_make_prim_w_arity
 # if MZSCHEME_VERSION_MAJOR < 299
@@ -403,6 +431,14 @@
 #  define scheme_char_string_to_path \
     dll_scheme_char_string_to_path
 # endif
+# define scheme_make_hash_table dll_scheme_make_hash_table
+# define scheme_hash_set dll_scheme_hash_set
+# define scheme_hash_get dll_scheme_hash_get
+# define scheme_make_double dll_scheme_make_double
+# ifdef INCLUDE_MZSCHEME_BASE
+#  define scheme_make_sized_byte_string dll_scheme_make_sized_byte_string
+#  define scheme_namespace_require dll_scheme_namespace_require
+# endif
 
 typedef struct
 {
@@ -468,7 +504,6 @@
     {"scheme_make_closed_prim_w_arity",
 	(void **)&dll_scheme_make_closed_prim_w_arity},
     {"scheme_make_integer_value", (void **)&dll_scheme_make_integer_value},
-    {"scheme_make_namespace", (void **)&dll_scheme_make_namespace},
     {"scheme_make_pair", (void **)&dll_scheme_make_pair},
     {"scheme_make_prim_w_arity", (void **)&dll_scheme_make_prim_w_arity},
 # if MZSCHEME_VERSION_MAJOR < 299
@@ -502,9 +537,16 @@
     {"scheme_current_config", (void **)&dll_scheme_current_config},
     {"scheme_char_string_to_byte_string",
 	(void **)&dll_scheme_char_string_to_byte_string},
-    {"scheme_char_string_to_path",
-	(void **)&dll_scheme_char_string_to_path},
+    {"scheme_char_string_to_path", (void **)&dll_scheme_char_string_to_path},
 # endif
+    {"scheme_make_hash_table", (void **)&dll_scheme_make_hash_table},
+    {"scheme_hash_set", (void **)&dll_scheme_hash_set},
+    {"scheme_hash_get", (void **)&dll_scheme_hash_get},
+    {"scheme_make_double", (void **)&dll_scheme_make_double},
+# ifdef INCLUDE_MZSCHEME_BASE
+    {"scheme_make_sized_byte_string", (void **)&dll_scheme_make_sized_byte_string},
+    {"scheme_namespace_require", (void **)&dll_scheme_namespace_require},
+#endif
     {NULL, NULL}};
 
 static HINSTANCE hMzGC = 0;
@@ -592,6 +634,11 @@
 }
 #endif /* DYNAMIC_MZSCHEME */
 
+/* need to put it here for dynamic stuff to work */
+#ifdef INCLUDE_MZSCHEME_BASE
+# include "mzscheme_base.c"
+#endif
+
 /*
  *========================================================================
  *  1. MzScheme interpreter startup
@@ -601,21 +648,22 @@
 static Scheme_Type mz_buffer_type;
 static Scheme_Type mz_window_type;
 
-static int initialized = 0;
+static int initialized = FALSE;
 
 /* global environment */
 static Scheme_Env    *environment = NULL;
 /* output/error handlers */
 static Scheme_Object *curout = NULL;
 static Scheme_Object *curerr = NULL;
-/* vim:exn exception */
+/* exn:vim exception */
 static Scheme_Object *exn_catching_apply = NULL;
 static Scheme_Object *exn_p = NULL;
 static Scheme_Object *exn_message = NULL;
 static Scheme_Object *vim_exn = NULL; /* Vim Error exception */
- /* values for exn:vim - constructor, predicate, accessors etc */
-static Scheme_Object *vim_exn_names = NULL;
-static Scheme_Object *vim_exn_values = NULL;
+
+#if !defined(MZ_PRECISE_GC) || MZSCHEME_VERSION_MAJOR < 400
+static void *stack_base = NULL;
+#endif
 
 static long range_start;
 static long range_end;
@@ -668,10 +716,10 @@
 timer_proc(HWND hwnd, UINT uMsg, UINT idEvent, DWORD dwTime)
 # elif defined(FEAT_GUI_GTK)
     static gint
-timer_proc(gpointer data UNUSED)
+timer_proc(gpointer data)
 # elif defined(FEAT_GUI_MOTIF) || defined(FEAT_GUI_ATHENA)
     static void
-timer_proc(XtPointer timed_out UNUSED, XtIntervalId *interval_id UNUSED)
+timer_proc(XtPointer timed_out, XtIntervalId *interval_id)
 # elif defined(FEAT_GUI_MAC)
     pascal void
 timer_proc(EventLoopTimerRef theTimer, void *userData)
@@ -751,12 +799,64 @@
 #endif
 }
 
+    void
+mzscheme_main(void)
+{
+#if defined(MZ_PRECISE_GC) && MZSCHEME_VERSION_MAJOR >= 400
+    /* use trampoline for precise GC in MzScheme >= 4.x */
+    scheme_main_setup(TRUE, mzscheme_env_main, 0, NULL);
+#else
+    mzscheme_env_main(NULL, 0, NULL);
+#endif
+}
+
+    static int
+mzscheme_env_main(Scheme_Env *env, int argc, char **argv)
+{
+    /* neither argument nor return values are used */
+#ifdef MZ_PRECISE_GC
+# if MZSCHEME_VERSION_MAJOR < 400
+    /*
+     * Starting from version 4.x, embedding applications must use
+     * scheme_main_setup/scheme_main_stack_setup trampolines
+     * rather than setting stack base directly with scheme_set_stack_base
+     */
+    Scheme_Object   *dummy = NULL;
+    MZ_GC_DECL_REG(1);
+    MZ_GC_VAR_IN_REG(0, dummy);
+
+    stack_base = &__gc_var_stack__;
+# else
+    /* environment has been created by us by Scheme */
+    environment = env;
+# endif
+    /*
+     * In 4.x, all activities must be performed inside trampoline
+     * so we are forced to initialise GC immediately
+     * This can be postponed in 3.x but I see no point in implementing
+     * a feature which will work in older versions only.
+     * One would better use conservative GC if he needs dynamic MzScheme
+     */
+    mzscheme_init();
+#else
+    int dummy = 0;
+    stack_base = (void *)&dummy;
+#endif
+    main_loop(FALSE, FALSE);
+#if defined(MZ_PRECISE_GC) && MZSCHEME_VERSION_MAJOR < 400
+    /* releasing dummy */
+    MZ_GC_REG();
+    MZ_GC_UNREG();
+#endif
+    return 0;
+}
+
     static void
 startup_mzscheme(void)
 {
-    Scheme_Object *proc_make_security_guard;
-
-    scheme_set_stack_base(NULL, 1);
+#if !defined(MZ_PRECISE_GC) || MZSCHEME_VERSION_MAJOR < 400
+    scheme_set_stack_base(stack_base, 1);
+#endif
 
     MZ_REGISTER_STATIC(environment);
     MZ_REGISTER_STATIC(curout);
@@ -765,10 +865,35 @@
     MZ_REGISTER_STATIC(exn_p);
     MZ_REGISTER_STATIC(exn_message);
     MZ_REGISTER_STATIC(vim_exn);
-    MZ_REGISTER_STATIC(vim_exn_names);
-    MZ_REGISTER_STATIC(vim_exn_values);
 
+#if !defined(MZ_PRECISE_GC) || MZSCHEME_VERSION_MAJOR < 400
+    /* in newer versions of precise GC the initial env has been created */
     environment = scheme_basic_env();
+#endif
+    MZ_GC_CHECK();
+
+#ifdef INCLUDE_MZSCHEME_BASE
+    {
+	/*
+	 * versions 4.x do not provide Scheme bindings by defaults
+	 * we need to add them explicitly
+	 */
+	Scheme_Object *scheme_base_symbol = NULL;
+	MZ_GC_DECL_REG(1);
+	MZ_GC_VAR_IN_REG(0, scheme_base_symbol);
+	MZ_GC_REG();
+	/* invoke function from generated and included base.c */
+	declare_modules(environment);
+	scheme_base_symbol = scheme_intern_symbol("scheme/base");
+	MZ_GC_CHECK();
+	scheme_namespace_require(scheme_base_symbol);
+	MZ_GC_CHECK();
+	MZ_GC_UNREG();
+    }
+#endif
+    register_vim_exn();
+    /* use new environment to initialise exception handling */
+    init_exn_catching_apply();
 
     /* redirect output */
     scheme_console_output = do_output;
@@ -776,48 +901,131 @@
 
 #ifdef MZSCHEME_COLLECTS
     /* setup 'current-library-collection-paths' parameter */
-    scheme_set_param(scheme_config, MZCONFIG_COLLECTION_PATHS,
-	    scheme_make_pair(
 # if MZSCHEME_VERSION_MAJOR >= 299
-		scheme_char_string_to_path(
-		    scheme_byte_string_to_char_string(
-			scheme_make_byte_string(MZSCHEME_COLLECTS))),
+    {
+	Scheme_Object	*coll_byte_string = NULL;
+	Scheme_Object	*coll_char_string = NULL;
+	Scheme_Object	*coll_path = NULL;
+	Scheme_Object	*coll_pair = NULL;
+	Scheme_Config	*config = NULL;
+
+	MZ_GC_DECL_REG(5);
+	MZ_GC_VAR_IN_REG(0, coll_byte_string);
+	MZ_GC_VAR_IN_REG(1, coll_char_string);
+	MZ_GC_VAR_IN_REG(2, coll_path);
+	MZ_GC_VAR_IN_REG(3, coll_pair);
+	MZ_GC_VAR_IN_REG(4, config);
+	MZ_GC_REG();
+	coll_byte_string = scheme_make_byte_string(MZSCHEME_COLLECTS);
+	MZ_GC_CHECK();
+	coll_char_string = scheme_byte_string_to_char_string(coll_byte_string);
+	MZ_GC_CHECK();
+	coll_path = scheme_char_string_to_path(coll_char_string);
+	MZ_GC_CHECK();
+	coll_pair = scheme_make_pair(coll_path, scheme_null);
+	MZ_GC_CHECK();
+	config = scheme_config;
+	MZ_GC_CHECK();
+	scheme_set_param(config, MZCONFIG_COLLECTION_PATHS, coll_pair);
+	MZ_GC_CHECK();
+	MZ_GC_UNREG();
+    }
 # else
-		scheme_make_string(MZSCHEME_COLLECTS),
+    {
+	Scheme_Object	*coll_string = NULL;
+	Scheme_Object	*coll_pair = NULL;
+	Scheme_Config	*config = NULL;
+
+	MZ_GC_DECL_REG(3);
+	MZ_GC_VAR_IN_REG(0, coll_string);
+	MZ_GC_VAR_IN_REG(1, coll_pair);
+	MZ_GC_VAR_IN_REG(2, config);
+	MZ_GC_REG();
+	coll_string = scheme_make_string(MZSCHEME_COLLECTS);
+	MZ_GC_CHECK();
+	coll_pair = scheme_make_pair(coll_string, scheme_null);
+	MZ_GC_CHECK();
+	config = scheme_config;
+	MZ_GC_CHECK();
+	scheme_set_param(config, MZCONFIG_COLLECTION_PATHS, coll_pair);
+	MZ_GC_CHECK();
+	MZ_GC_UNREG();
+    }
 # endif
-		scheme_null));
 #endif
 #ifdef HAVE_SANDBOX
-    /* setup sandbox guards */
-    proc_make_security_guard = scheme_lookup_global(
-	    scheme_intern_symbol("make-security-guard"),
-	    environment);
-    if (proc_make_security_guard != NULL)
     {
-	Scheme_Object *args[3];
-	Scheme_Object *guard;
-	args[0] = scheme_get_param(scheme_config, MZCONFIG_SECURITY_GUARD);
-	args[1] = scheme_make_prim_w_arity(sandbox_file_guard,
-		"sandbox-file-guard", 3, 3);
-	args[2] = scheme_make_prim_w_arity(sandbox_network_guard,
-		"sandbox-network-guard", 4, 4);
-	guard = scheme_apply(proc_make_security_guard, 3, args);
-	scheme_set_param(scheme_config, MZCONFIG_SECURITY_GUARD, guard);
+	Scheme_Object	*make_security_guard = NULL;
+	MZ_GC_DECL_REG(1);
+	MZ_GC_VAR_IN_REG(0, make_security_guard);
+	MZ_GC_REG();
+
+#if MZSCHEME_VERSION_MAJOR < 400
+	{
+	    Scheme_Object	*make_security_guard_symbol = NULL;
+	    MZ_GC_DECL_REG(1);
+	    MZ_GC_VAR_IN_REG(0, make_security_guard_symbol);
+	    MZ_GC_REG();
+	    make_security_guard_symbol = scheme_intern_symbol("make-security-guard");
+	    MZ_GC_CHECK();
+	    make_security_guard = scheme_lookup_global(
+		    make_security_guard_symbol, environment);
+	    MZ_GC_UNREG();
+	}
+#else
+	make_security_guard = scheme_builtin_value("make-security-guard");
+	MZ_GC_CHECK();
+#endif
+
+	/* setup sandbox guards */
+	if (make_security_guard != NULL)
+	{
+	    Scheme_Object   *args[3] = {NULL, NULL, NULL};
+	    Scheme_Object   *guard = NULL;
+	    Scheme_Config   *config = NULL;
+	    MZ_GC_DECL_REG(5);
+	    MZ_GC_ARRAY_VAR_IN_REG(0, args, 3);
+	    MZ_GC_VAR_IN_REG(3, guard);
+	    MZ_GC_VAR_IN_REG(4, config);
+	    MZ_GC_REG();
+	    config = scheme_config;
+	    MZ_GC_CHECK();
+	    args[0] = scheme_get_param(config, MZCONFIG_SECURITY_GUARD);
+	    MZ_GC_CHECK();
+	    args[1] = scheme_make_prim_w_arity(sandbox_file_guard,
+		    "sandbox-file-guard", 3, 3);
+	    args[2] = scheme_make_prim_w_arity(sandbox_network_guard,
+		    "sandbox-network-guard", 4, 4);
+	    guard = scheme_apply(make_security_guard, 3, args);
+	    MZ_GC_CHECK();
+	    scheme_set_param(config, MZCONFIG_SECURITY_GUARD, guard);
+	    MZ_GC_CHECK();
+	    MZ_GC_UNREG();
+	}
+	MZ_GC_UNREG();
     }
 #endif
     /* Create buffer and window types for use in Scheme code */
     mz_buffer_type = scheme_make_type("<vim-buffer>");
+    MZ_GC_CHECK();
     mz_window_type = scheme_make_type("<vim-window>");
+    MZ_GC_CHECK();
+#ifdef MZ_PRECISE_GC
+    GC_register_traversers(mz_buffer_type,
+	    buffer_size_proc, buffer_mark_proc, buffer_fixup_proc,
+	    TRUE, TRUE);
+    GC_register_traversers(mz_window_type,
+	    window_size_proc, window_mark_proc, window_fixup_proc,
+	    TRUE, TRUE);
+#endif
 
-    register_vim_exn(environment);
-    make_modules(environment);
+    make_modules();
 
     /*
      * setup callback to receive notifications
      * whether thread scheduling is (or not) required
      */
     scheme_notify_multithread = notify_multithread;
-    initialized = 1;
 }
 
 /*
@@ -827,102 +1035,66 @@
     static int
 mzscheme_init(void)
 {
-    int do_require = FALSE;
-
     if (!initialized)
     {
-	do_require = TRUE;
 #ifdef DYNAMIC_MZSCHEME
 	if (!mzscheme_enabled(TRUE))
 	{
-	    EMSG(_("???: Sorry, this command is disabled, the MzScheme library could not be loaded."));
+	    EMSG(_("E812: Sorry, this command is disabled, the MzScheme libraries could not be loaded."));
 	    return -1;
 	}
 #endif
 	startup_mzscheme();
-
-	if (mzscheme_io_init())
-	    return -1;
-
+	initialized = TRUE;
     }
-    /* recreate ports each call effectivelly clearing these ones */
-    curout = scheme_make_string_output_port();
-    curerr = scheme_make_string_output_port();
-    scheme_set_param(scheme_config, MZCONFIG_OUTPUT_PORT, curout);
-    scheme_set_param(scheme_config, MZCONFIG_ERROR_PORT, curerr);
-
-    if (do_require)
     {
-	/* auto-instantiate in basic env */
-	eval_in_namespace("(require (prefix vimext: vimext))", do_eval,
-		environment, NULL);
+	Scheme_Config	*config = NULL;
+	MZ_GC_DECL_REG(1);
+	MZ_GC_VAR_IN_REG(0, config);
+	MZ_GC_REG();
+	config = scheme_config;
+	MZ_GC_CHECK();
+	/* recreate ports each call effectivelly clearing these ones */
+	curout = scheme_make_string_output_port();
+	MZ_GC_CHECK();
+	curerr = scheme_make_string_output_port();
+	MZ_GC_CHECK();
+	scheme_set_param(config, MZCONFIG_OUTPUT_PORT, curout);
+	MZ_GC_CHECK();
+	scheme_set_param(config, MZCONFIG_ERROR_PORT, curerr);
+	MZ_GC_CHECK();
+	MZ_GC_UNREG();
     }
 
     return 0;
 }
 
 /*
- * This routine fills the namespace with various important routines that can
- * be used within MzScheme.
- */
-    static void
-mzscheme_interface_init(vim_mz_buffer *mzbuff)
-{
-    Scheme_Object   *attach;
-
-    mzbuff->env = (Scheme_Env *)scheme_make_namespace(0, NULL);
-
-    /*
-     * attach instantiated modules from global namespace
-     * so they can be easily instantiated in the buffer namespace
-     */
-    attach = scheme_lookup_global(
-	    scheme_intern_symbol("namespace-attach-module"),
-	    environment);
-
-    if (attach != NULL)
-    {
-	Scheme_Object   *ret;
-	Scheme_Object	*args[2];
-
-	args[0] = (Scheme_Object *)environment;
-	args[1] = scheme_intern_symbol("vimext");
-
-	ret = (Scheme_Object *)mzvim_apply(attach, 2, args);
-    }
-
-    add_vim_exn(mzbuff->env);
-}
-
-/*
  *========================================================================
  *  2.  External Interface
  *========================================================================
  */
 
 /*
- * Evaluate command in namespace with exception handling
+ * Evaluate command with exception handling
  */
     static int
-eval_in_namespace(void *data, Scheme_Closed_Prim *what, Scheme_Env *env,
-		Scheme_Object **ret)
+eval_with_exn_handling(void *data, Scheme_Closed_Prim *what, Scheme_Object **ret)
 {
-    Scheme_Object   *value;
-    Scheme_Object   *exn;
-    Cmd_Info	    info;   /* closure info */
+    Scheme_Object   *value = NULL;
+    Scheme_Object   *exn = NULL;
+    Scheme_Object   *prim = NULL;
 
-    info.data = data;
-    info.env = env;
+    MZ_GC_DECL_REG(3);
+    MZ_GC_VAR_IN_REG(0, value);
+    MZ_GC_VAR_IN_REG(1, exn);
+    MZ_GC_VAR_IN_REG(2, prim);
+    MZ_GC_REG();
 
-    scheme_set_param(scheme_config, MZCONFIG_ENV,
-	    (Scheme_Object *) env);
-    /*
-     * ensure all evaluations will be in current buffer namespace,
-     * the second argument to scheme_eval_string isn't enough!
-     */
-    value = _apply_thunk_catch_exceptions(
-	    scheme_make_closed_prim_w_arity(what, &info, "mzvim", 0, 0),
-	    &exn);
+    prim = scheme_make_closed_prim_w_arity(what, data, "mzvim", 0, 0);
+    MZ_GC_CHECK();
+    value = _apply_thunk_catch_exceptions(prim, &exn);
+    MZ_GC_CHECK();
 
     if (!value)
     {
@@ -930,9 +1102,11 @@
 	/* Got an exn? */
 	if (value)
 	{
-	    scheme_display(value, curerr);  /*  Send to stderr-vim */
+	    scheme_display(value, curerr);   /*  Send to stderr-vim */
+	    MZ_GC_CHECK();
 	    do_flush();
 	}
+	MZ_GC_UNREG();
 	/* `raise' was called on some arbitrary value */
 	return FAIL;
     }
@@ -941,9 +1115,13 @@
 	*ret = value;
     /* Print any result, as long as it's not a void */
     else if (!SCHEME_VOIDP(value))
+    {
 	scheme_display(value, curout);  /* Send to stdout-vim */
+	MZ_GC_CHECK();
+    }
 
     do_flush();
+    MZ_GC_UNREG();
     return OK;
 }
 
@@ -957,7 +1135,7 @@
     range_start = eap->line1;
     range_end = eap->line2;
 
-    return eval_in_namespace(data, what, get_vim_curr_buffer()->env, NULL);
+    return eval_with_exn_handling(data, what, NULL);
 }
 
 /*
@@ -974,6 +1152,7 @@
 	bp->buf = INVALID_BUFFER_VALUE;
 	buf->b_mzscheme_ref = NULL;
 	scheme_gc_ptr_ok(bp);
+	MZ_GC_CHECK();
     }
 }
 
@@ -990,6 +1169,7 @@
 	wp->win = INVALID_WINDOW_VALUE;
 	win->w_mzscheme_ref = NULL;
 	scheme_gc_ptr_ok(wp);
+	MZ_GC_CHECK();
     }
 }
 
@@ -1014,18 +1194,6 @@
     }
 }
 
-/* eval MzScheme string */
-    void *
-mzvim_eval_string(char_u *str)
-{
-    Scheme_Object *ret = NULL;
-    if (mzscheme_init())
-	return FAIL;
-
-    eval_in_namespace(str, do_eval, get_vim_curr_buffer()->env, &ret);
-    return ret;
-}
-
 /*
  * apply MzScheme procedure with arguments,
  * handling errors
@@ -1033,43 +1201,65 @@
     Scheme_Object *
 mzvim_apply(Scheme_Object *proc, int argc, Scheme_Object **argv)
 {
-    Apply_Info	data;
-    Scheme_Object *ret = NULL;
-
     if (mzscheme_init())
 	return FAIL;
+    else
+    {
+	Apply_Info	data = {NULL, 0, NULL};
+	Scheme_Object	*ret = NULL;
 
-    data.proc = proc;
-    data.argc = argc;
-    data.argv = argv;
+	MZ_GC_DECL_REG(5);
+	MZ_GC_VAR_IN_REG(0, ret);
+	MZ_GC_VAR_IN_REG(1, data.proc);
+	MZ_GC_ARRAY_VAR_IN_REG(2, data.argv, argc);
+	MZ_GC_REG();
 
-    eval_in_namespace(&data, do_apply, get_vim_curr_buffer()->env, &ret);
-    return ret;
+	data.proc = proc;
+	data.argc = argc;
+	data.argv = argv;
+
+	eval_with_exn_handling(&data, do_apply, &ret);
+	MZ_GC_UNREG();
+	return ret;
+    }
 }
 
     static Scheme_Object *
 do_load(void *data, int noargc, Scheme_Object **noargv)
 {
-    Cmd_Info	    *info = (Cmd_Info *)data;
-    Scheme_Object   *result = scheme_void;
-    Scheme_Object   *expr;
-    char_u	    *file = scheme_malloc_fail_ok(
-					  scheme_malloc_atomic, MAXPATHL + 1);
-    Port_Info	    *pinfo = (Port_Info *)(info->data);
+    Scheme_Object   *expr = NULL;
+    Scheme_Object   *result = NULL;
+    char	    *file = NULL;
+    Port_Info	    *pinfo = (Port_Info *)data;
+
+    MZ_GC_DECL_REG(3);
+    MZ_GC_VAR_IN_REG(0, expr);
+    MZ_GC_VAR_IN_REG(1, result);
+    MZ_GC_VAR_IN_REG(2, file);
+    MZ_GC_REG();
+
+    file = (char *)scheme_malloc_fail_ok(scheme_malloc_atomic, MAXPATHL + 1);
+    MZ_GC_CHECK();
 
     /* make Vim expansion */
-    expand_env((char_u *)pinfo->name, file, MAXPATHL);
-    /* scheme_load looks strange working with namespaces and error handling*/
+    expand_env((char_u *)pinfo->name, (char_u *)file, MAXPATHL);
     pinfo->port = scheme_open_input_file(file, "mzfile");
-    scheme_count_lines(pinfo->port); /* to get accurate read error location*/
+    MZ_GC_CHECK();
+    scheme_count_lines(pinfo->port);  /* to get accurate read error location*/
+    MZ_GC_CHECK();
 
     /* Like REPL but print only last result */
     while (!SCHEME_EOFP(expr = scheme_read(pinfo->port)))
-	result = scheme_eval(expr, info->env);
+    {
+	result = scheme_eval(expr, environment);
+	MZ_GC_CHECK();
+    }
 
     /* errors will be caught in do_mzscheme_comamnd and ex_mzfile */
     scheme_close_input_port(pinfo->port);
+    MZ_GC_CHECK();
     pinfo->port = NULL;
+    MZ_GC_UNREG();
     return result;
 }
 
@@ -1077,13 +1267,20 @@
     void
 ex_mzfile(exarg_T *eap)
 {
-    Port_Info	pinfo;
+    Port_Info	pinfo = {NULL, NULL};
+
+    MZ_GC_DECL_REG(1);
+    MZ_GC_VAR_IN_REG(0, pinfo.port);
+    MZ_GC_REG();
 
     pinfo.name = (char *)eap->arg;
-    pinfo.port = NULL;
     if (do_mzscheme_command(eap, &pinfo, do_load) != OK
 	    && pinfo.port != NULL)	/* looks like port was not closed */
+    {
 	scheme_close_input_port(pinfo.port);
+	MZ_GC_CHECK();
+    }
+    MZ_GC_UNREG();
 }
 
 
@@ -1103,14 +1300,12 @@
 		"(with-handlers ([void (lambda (exn) (cons #f exn))]) "
 		"(cons #t (thunk))))";
 
-	/* make sure we have a namespace with the standard syntax: */
-	Scheme_Env *env = (Scheme_Env *)scheme_make_namespace(0, NULL);
-	add_vim_exn(env);
-
-	exn_catching_apply = scheme_eval_string(e, env);
-	exn_p = scheme_lookup_global(scheme_intern_symbol("exn?"), env);
-	exn_message = scheme_lookup_global(
-		scheme_intern_symbol("exn-message"), env);
+	exn_catching_apply = scheme_eval_string(e, environment);
+	MZ_GC_CHECK();
+	exn_p = scheme_builtin_value("exn?");
+	MZ_GC_CHECK();
+	exn_message = scheme_builtin_value("exn-message");
+	MZ_GC_CHECK();
     }
 }
 
@@ -1124,8 +1319,6 @@
 {
     Scheme_Object *v;
 
-    init_exn_catching_apply();
-
     v = _scheme_apply(exn_catching_apply, 1, &f);
     /* v is a pair: (cons #t value) or (cons #f exn) */
 
@@ -1141,8 +1334,6 @@
     static Scheme_Object *
 extract_exn_message(Scheme_Object *v)
 {
-    init_exn_catching_apply();
-
     if (SCHEME_TRUEP(_scheme_apply(exn_p, 1, &v)))
 	return _scheme_apply(exn_message, 1, &v);
     else
@@ -1152,16 +1343,13 @@
     static Scheme_Object *
 do_eval(void *s, int noargc, Scheme_Object **noargv)
 {
-    Cmd_Info	*info = (Cmd_Info *)s;
-
-    return scheme_eval_string_all((char *)(info->data), info->env, TRUE);
+    return scheme_eval_string_all((char *)s, environment, TRUE);
 }
 
     static Scheme_Object *
 do_apply(void *a, int noargc, Scheme_Object **noargv)
 {
-    Apply_Info	*info = (Apply_Info *)(((Cmd_Info *)a)->data);
-
+    Apply_Info	*info = (Apply_Info *)a;
     return scheme_apply(info->proc, info->argc, info->argv);
 }
 
@@ -1219,6 +1407,7 @@
     long length;
 
     buff = scheme_get_sized_string_output(curerr, &length);
+    MZ_GC_CHECK();
     if (length)
     {
 	do_err_output(buff, length);
@@ -1226,17 +1415,11 @@
     }
 
     buff = scheme_get_sized_string_output(curout, &length);
+    MZ_GC_CHECK();
     if (length)
 	do_output(buff, length);
 }
 
-    static int
-mzscheme_io_init(void)
-{
-    /* Nothing needed so far... */
-    return 0;
-}
-
 /*
  *========================================================================
  *  4. Implementation of the Vim Features for MzScheme
@@ -1263,22 +1446,30 @@
 vim_eval(void *data, int argc, Scheme_Object **argv)
 {
 #ifdef FEAT_EVAL
-    Vim_Prim	    *prim = (Vim_Prim *)data;
-    char	    *expr;
-    char	    *str;
-    Scheme_Object   *result;
+    Vim_Prim		*prim = (Vim_Prim *)data;
+    char		*expr;
+    Scheme_Object	*result;
+    /* hash table to store visited values to avoid infinite loops */
+    Scheme_Hash_Table	*visited = NULL;
+    typval_T		*vim_result;
+
+    MZ_GC_DECL_REG(1);
+    MZ_GC_VAR_IN_REG(0, visited);
+    MZ_GC_REG();
+
+    visited = scheme_make_hash_table(SCHEME_hash_ptr);
+    MZ_GC_CHECK();
 
     expr = SCHEME_STR_VAL(GUARANTEE_STRING(prim->name, 0));
+    vim_result = eval_expr((char_u *)expr, NULL);
 
-    str = (char *)eval_to_string((char_u *)expr, NULL, TRUE);
-
-    if (str == NULL)
+    if (vim_result == NULL)
 	raise_vim_exn(_("invalid expression"));
 
-    result = scheme_make_string(str);
+    result = vim_to_mzscheme(vim_result, 1, visited);
+    free_tv(vim_result);
 
-    vim_free(str);
-
+    MZ_GC_UNREG();
     return result;
 #else
     raise_vim_exn(_("expressions disabled at compile time"));
@@ -1318,7 +1509,7 @@
     Vim_Prim	    *prim = (Vim_Prim *)data;
     char_u	    *name;
     long	    value;
-    char_u	    *strval;
+    char	    *strval;
     int		    rc;
     Scheme_Object   *rval;
     int		    opt_flags = 0;
@@ -1333,6 +1524,7 @@
 	{
 	    MZ_REGISTER_STATIC(M_global);
 	    M_global = scheme_intern_symbol("global");
+	    MZ_GC_CHECK();
 	}
 
 	if (argv[1] == M_global)
@@ -1354,7 +1546,7 @@
 	    scheme_wrong_type(prim->name, "vim-buffer/window", 1, argc, argv);
     }
 
-    rc = get_option_value(name, &value, &strval, opt_flags);
+    rc = get_option_value(name, &value, (char_u **)&strval, opt_flags);
     curbuf = save_curb;
     curwin = save_curw;
 
@@ -1364,6 +1556,7 @@
 	return scheme_make_integer_value(value);
     case 0:
 	rval = scheme_make_string(strval);
+	MZ_GC_CHECK();
 	vim_free(strval);
 	return rval;
     case -1:
@@ -1393,6 +1586,7 @@
 	{
 	    MZ_REGISTER_STATIC(M_global);
 	    M_global = scheme_intern_symbol("global");
+	    MZ_GC_CHECK();
 	}
 
 	if (argv[1] == M_global)
@@ -1463,7 +1657,10 @@
 
     for (w = firstwin; w != NULL; w = w->w_next)
 	if (w->w_buffer == buf->buf)
+	{
 	    list = scheme_make_pair(window_new(w), list);
+	    MZ_GC_CHECK();
+	}
 
     return list;
 }
@@ -1471,7 +1668,11 @@
     static Scheme_Object *
 window_new(win_T *win)
 {
-    vim_mz_window *self;
+    vim_mz_window *self = NULL;
+
+    MZ_GC_DECL_REG(1);
+    MZ_GC_VAR_IN_REG(0, self);
+    MZ_GC_REG();
 
     /* We need to handle deletion of windows underneath us.
      * If we add a "w_mzscheme_ref" field to the win_T structure,
@@ -1485,13 +1686,14 @@
 	return win->w_mzscheme_ref;
 
     self = scheme_malloc_fail_ok(scheme_malloc, sizeof(vim_mz_window));
-
     vim_memset(self, 0, sizeof(vim_mz_window));
     scheme_dont_gc_ptr(self);	/* because win isn't visible to GC */
+    MZ_GC_CHECK();
     win->w_mzscheme_ref = self;
     self->win = win;
-    self->tag = mz_window_type;
+    self->so.type = mz_window_type;
 
+    MZ_GC_UNREG();
     return (Scheme_Object *)(self);
 }
 
@@ -1660,7 +1862,6 @@
 /*
  *===========================================================================
  *  6. Vim Buffer-related Manipulation Functions
- *     Note that each buffer should have its own private namespace.
  *===========================================================================
  */
 
@@ -1669,14 +1870,14 @@
 mzscheme_open_buffer(void *data, int argc, Scheme_Object **argv)
 {
     Vim_Prim	    *prim = (Vim_Prim *)data;
-    char	    *fname;
+    char_u	    *fname;
     int		    num = 0;
     Scheme_Object   *onum;
 
 #ifdef HAVE_SANDBOX
     sandbox_check();
 #endif
-    fname = SCHEME_STR_VAL(GUARANTEE_STRING(prim->name, 0));
+    fname = (char_u *)SCHEME_STR_VAL(GUARANTEE_STRING(prim->name, 0));
     /* TODO make open existing file */
     num = buflist_add(fname, BLN_LISTED | BLN_CURBUF);
 
@@ -1712,7 +1913,7 @@
     buf_T	*buf;
     char_u	*fname;
 
-    fname = SCHEME_STR_VAL(GUARANTEE_STRING(prim->name, 0));
+    fname = (char_u *)SCHEME_STR_VAL(GUARANTEE_STRING(prim->name, 0));
 
     for (buf = firstbuf; buf; buf = buf->b_next)
 	if (buf->b_ffname == NULL || buf->b_sfname == NULL)
@@ -1783,7 +1984,7 @@
     Vim_Prim	    *prim = (Vim_Prim *)data;
     vim_mz_buffer   *buf = get_buffer_arg(prim->name, 0, argc, argv);
 
-    return scheme_make_string(buf->buf->b_ffname);
+    return scheme_make_string((char *)buf->buf->b_ffname);
 }
 
 /* (curr-buff) */
@@ -1796,7 +1997,11 @@
     static Scheme_Object *
 buffer_new(buf_T *buf)
 {
-    vim_mz_buffer *self;
+    vim_mz_buffer *self = NULL;
+
+    MZ_GC_DECL_REG(1);
+    MZ_GC_VAR_IN_REG(0, self);
+    MZ_GC_REG();
 
     /* We need to handle deletion of buffers underneath us.
      * If we add a "b_mzscheme_ref" field to the buf_T structure,
@@ -1806,15 +2011,14 @@
 	return buf->b_mzscheme_ref;
 
     self = scheme_malloc_fail_ok(scheme_malloc, sizeof(vim_mz_buffer));
-
     vim_memset(self, 0, sizeof(vim_mz_buffer));
-    scheme_dont_gc_ptr(self);	/* because buf isn't visible to GC */
+    scheme_dont_gc_ptr(self); /* because buf isn't visible to GC */
+    MZ_GC_CHECK();
     buf->b_mzscheme_ref = self;
     self->buf = buf;
-    self->tag = mz_buffer_type;
+    self->so.type = mz_buffer_type;
 
-    mzscheme_interface_init(self);	/* Set up namespace */
-
+    MZ_GC_UNREG();
     return (Scheme_Object *)(self);
 }
 
@@ -1845,14 +2049,14 @@
     Vim_Prim	    *prim = (Vim_Prim *)data;
     vim_mz_buffer   *buf;
     int		    linenr;
-    char	    *line;
+    char_u	    *line;
 
     buf = get_buffer_arg(prim->name, 1, argc, argv);
     linenr = SCHEME_INT_VAL(GUARANTEE_INTEGER(prim->name, 0));
     line = ml_get_buf(buf->buf, (linenr_T)linenr, FALSE);
 
     raise_if_error();
-    return scheme_make_string(line);
+    return scheme_make_string((char *)line);
 }
 
 
@@ -1869,7 +2073,11 @@
     Vim_Prim	    *prim = (Vim_Prim *)data;
     vim_mz_buffer   *buf;
     int		    i, hi, lo, n;
-    Scheme_Object   *list;
+    Scheme_Object   *list = NULL;
+
+    MZ_GC_DECL_REG(1);
+    MZ_GC_VAR_IN_REG(0, list);
+    MZ_GC_REG();
 
     buf = get_buffer_arg(prim->name, 2, argc, argv);
     list = scheme_null;
@@ -1897,8 +2105,9 @@
 
 	/* Set the list item */
 	list = scheme_make_pair(str, list);
+	MZ_GC_CHECK();
     }
-
+    MZ_GC_UNREG();
     return list;
 }
 
@@ -1925,11 +2134,14 @@
      */
     Vim_Prim	    *prim = (Vim_Prim *)data;
     vim_mz_buffer   *buf;
-    Scheme_Object   *line;
+    Scheme_Object   *line = NULL;
     char	    *save;
-    buf_T	    *savebuf;
     int		    n;
 
+    MZ_GC_DECL_REG(1);
+    MZ_GC_VAR_IN_REG(0, line);
+    MZ_GC_REG();
+
 #ifdef HAVE_SANDBOX
     sandbox_check();
 #endif
@@ -1943,7 +2155,8 @@
 
     if (SCHEME_FALSEP(line))
     {
-	savebuf = curbuf;
+	buf_T	    *savebuf = curbuf;
+
 	curbuf = buf->buf;
 
 	if (u_savedel((linenr_T)n, 1L) == FAIL)
@@ -1962,33 +2175,56 @@
 
 	curbuf = savebuf;
 
+	MZ_GC_UNREG();
 	raise_if_error();
 	return scheme_void;
     }
-
-    /* Otherwise it's a line */
-    save = string_to_line(line);
-    savebuf = curbuf;
-
-    curbuf = buf->buf;
-
-    if (u_savesub((linenr_T)n) == FAIL)
-    {
-	curbuf = savebuf;
-	raise_vim_exn(_("cannot save undo information"));
-    }
-    else if (ml_replace((linenr_T)n, (char_u *)save, TRUE) == FAIL)
-    {
-	curbuf = savebuf;
-	raise_vim_exn(_("cannot replace line"));
-    }
     else
-	changed_bytes((linenr_T)n, 0);
+    {
+	/* Otherwise it's a line */
+	buf_T	    *savebuf = curbuf;
 
-    curbuf = savebuf;
+	save = string_to_line(line);
 
-    raise_if_error();
-    return scheme_void;
+	curbuf = buf->buf;
+
+	if (u_savesub((linenr_T)n) == FAIL)
+	{
+	    curbuf = savebuf;
+	    vim_free(save);
+	    raise_vim_exn(_("cannot save undo information"));
+	}
+	else if (ml_replace((linenr_T)n, (char_u *)save, TRUE) == FAIL)
+	{
+	    curbuf = savebuf;
+	    vim_free(save);
+	    raise_vim_exn(_("cannot replace line"));
+	}
+	else
+	{
+	    vim_free(save);
+	    changed_bytes((linenr_T)n, 0);
+	}
+
+	curbuf = savebuf;
+
+	/* Check that the cursor is not beyond the end of the line now. */
+	if (buf->buf == curwin->w_buffer)
+	    check_cursor_col();
+
+	MZ_GC_UNREG();
+	raise_if_error();
+	return scheme_void;
+    }
+}
+
+    static void
+free_array(char **array)
+{
+    char **curr = array;
+    while (*curr != NULL)
+	vim_free(*curr++);
+    vim_free(array);
 }
 
 /*
@@ -2013,15 +2249,15 @@
      *	  3. Anything else - this is an error.
      */
     Vim_Prim	    *prim = (Vim_Prim *)data;
-    vim_mz_buffer   *buf;
-    Scheme_Object   *line_list;
-    Scheme_Object   *line;
-    Scheme_Object   *rest;
-    char	    **array;
-    buf_T	    *savebuf;
+    vim_mz_buffer   *buf = NULL;
+    Scheme_Object   *line_list = NULL;
     int		    i, old_len, new_len, hi, lo;
     long	    extra;
 
+    MZ_GC_DECL_REG(1);
+    MZ_GC_VAR_IN_REG(0, line_list);
+    MZ_GC_REG();
+
 #ifdef HAVE_SANDBOX
     sandbox_check();
 #endif
@@ -2047,7 +2283,7 @@
 
     if (SCHEME_FALSEP(line_list) || SCHEME_NULLP(line_list))
     {
-	savebuf = curbuf;
+	buf_T	*savebuf = curbuf;
 	curbuf = buf->buf;
 
 	if (u_savedel((linenr_T)lo, (long)old_len) == FAIL)
@@ -2070,98 +2306,121 @@
 
 	curbuf = savebuf;
 
+	MZ_GC_UNREG();
 	raise_if_error();
 	return scheme_void;
     }
-
-    /* List */
-    new_len = scheme_proper_list_length(line_list);
-    if (new_len < 0)	/* improper or cyclic list */
-	scheme_wrong_type(prim->name, "proper list",
-		2, argc, argv);
-
-    /* Using MzScheme allocator, so we don't need to free this and
-     * can safely keep pointers to GC collected strings
-     */
-    array = (char **)scheme_malloc_fail_ok(scheme_malloc,
-		(unsigned)(new_len * sizeof(char *)));
-
-    rest = line_list;
-    for (i = 0; i < new_len; ++i)
+    else
     {
-	line = SCHEME_CAR(rest);
-	rest = SCHEME_CDR(rest);
-	if (!SCHEME_STRINGP(line))
-	    scheme_wrong_type(prim->name, "string-list", 2, argc, argv);
-	array[i] = string_to_line(line);
-    }
+	buf_T	*savebuf = curbuf;
 
-    savebuf = curbuf;
-    curbuf = buf->buf;
+	/* List */
+	new_len = scheme_proper_list_length(line_list);
+	MZ_GC_CHECK();
+	if (new_len < 0)	/* improper or cyclic list */
+	    scheme_wrong_type(prim->name, "proper list",
+		    2, argc, argv);
+	else
+	{
+	    char		**array = NULL;
+	    Scheme_Object   *line = NULL;
+	    Scheme_Object   *rest = NULL;
 
-    if (u_save((linenr_T)(lo-1), (linenr_T)hi) == FAIL)
-    {
+	    MZ_GC_DECL_REG(2);
+	    MZ_GC_VAR_IN_REG(0, line);
+	    MZ_GC_VAR_IN_REG(1, rest);
+	    MZ_GC_REG();
+
+	    array = (char **)alloc(new_len * sizeof(char *));
+	    vim_memset(array, 0, new_len * sizeof(char *));
+
+	    rest = line_list;
+	    for (i = 0; i < new_len; ++i)
+	    {
+		line = SCHEME_CAR(rest);
+		rest = SCHEME_CDR(rest);
+		if (!SCHEME_STRINGP(line))
+		{
+		    free_array(array);
+		    scheme_wrong_type(prim->name, "string-list", 2, argc, argv);
+		}
+		array[i] = string_to_line(line);
+	    }
+
+	    curbuf = buf->buf;
+
+	    if (u_save((linenr_T)(lo-1), (linenr_T)hi) == FAIL)
+	    {
+		curbuf = savebuf;
+		free_array(array);
+		raise_vim_exn(_("cannot save undo information"));
+	    }
+
+	    /*
+	     * If the size of the range is reducing (ie, new_len < old_len) we
+	     * need to delete some old_len. We do this at the start, by
+	     * repeatedly deleting line "lo".
+	     */
+	    for (i = 0; i < old_len - new_len; ++i)
+	    {
+		if (ml_delete((linenr_T)lo, FALSE) == FAIL)
+		{
+		    curbuf = savebuf;
+		    free_array(array);
+		    raise_vim_exn(_("cannot delete line"));
+		}
+		extra--;
+	    }
+
+	    /*
+	     * For as long as possible, replace the existing old_len with the
+	     * new old_len. This is a more efficient operation, as it requires
+	     * less memory allocation and freeing.
+	     */
+	    for (i = 0; i < old_len && i < new_len; i++)
+		if (ml_replace((linenr_T)(lo+i), (char_u *)array[i], TRUE) == FAIL)
+		{
+		    curbuf = savebuf;
+		    free_array(array);
+		    raise_vim_exn(_("cannot replace line"));
+		}
+
+	    /*
+	     * Now we may need to insert the remaining new_len.  We don't need to
+	     * free the string passed back because MzScheme has control of that
+	     * memory.
+	     */
+	    while (i < new_len)
+	    {
+		if (ml_append((linenr_T)(lo + i - 1),
+			    (char_u *)array[i], 0, FALSE) == FAIL)
+		{
+		    curbuf = savebuf;
+		    free_array(array);
+		    raise_vim_exn(_("cannot insert line"));
+		}
+		++i;
+		++extra;
+	    }
+	    MZ_GC_UNREG();
+	    free_array(array);
+	}
+
+	/*
+	 * Adjust marks. Invalidate any which lie in the
+	 * changed range, and move any in the remainder of the buffer.
+	 */
+	mark_adjust((linenr_T)lo, (linenr_T)(hi - 1), (long)MAXLNUM, (long)extra);
+	changed_lines((linenr_T)lo, 0, (linenr_T)hi, (long)extra);
+
+	if (buf->buf == curwin->w_buffer)
+	    mz_fix_cursor(lo, hi, extra);
 	curbuf = savebuf;
-	raise_vim_exn(_("cannot save undo information"));
+
+	MZ_GC_UNREG();
+	raise_if_error();
+	return scheme_void;
     }
-
-    /*
-     * If the size of the range is reducing (ie, new_len < old_len) we
-     * need to delete some old_len. We do this at the start, by
-     * repeatedly deleting line "lo".
-     */
-    for (i = 0; i < old_len - new_len; ++i)
-    {
-	if (ml_delete((linenr_T)lo, FALSE) == FAIL)
-	{
-	    curbuf = savebuf;
-	    raise_vim_exn(_("cannot delete line"));
-	}
-	extra--;
-    }
-
-    /*
-     * For as long as possible, replace the existing old_len with the
-     * new old_len. This is a more efficient operation, as it requires
-     * less memory allocation and freeing.
-     */
-    for (i = 0; i < old_len && i < new_len; i++)
-	if (ml_replace((linenr_T)(lo+i), (char_u *)array[i], TRUE) == FAIL)
-	{
-	    curbuf = savebuf;
-	    raise_vim_exn(_("cannot replace line"));
-	}
-
-    /*
-     * Now we may need to insert the remaining new_len.  We don't need to
-     * free the string passed back because MzScheme has control of that
-     * memory.
-     */
-    while (i < new_len)
-    {
-	if (ml_append((linenr_T)(lo + i - 1),
-		(char_u *)array[i], 0, FALSE) == FAIL)
-	{
-	    curbuf = savebuf;
-	    raise_vim_exn(_("cannot insert line"));
-	}
-	++i;
-	++extra;
-    }
-
-    /*
-     * Adjust marks. Invalidate any which lie in the
-     * changed range, and move any in the remainder of the buffer.
-     */
-    mark_adjust((linenr_T)lo, (linenr_T)(hi - 1), (long)MAXLNUM, (long)extra);
-    changed_lines((linenr_T)lo, 0, (linenr_T)hi, (long)extra);
-
-    if (buf->buf == curwin->w_buffer)
-	mz_fix_cursor(lo, hi, extra);
-    curbuf = savebuf;
-
-    raise_if_error();
-    return scheme_void;
 }
 
 /*
@@ -2179,15 +2438,15 @@
 insert_buffer_line_list(void *data, int argc, Scheme_Object **argv)
 {
     Vim_Prim	    *prim = (Vim_Prim *)data;
-    vim_mz_buffer   *buf;
-    Scheme_Object   *list;
-    Scheme_Object   *line;
-    Scheme_Object   *rest;
-    char	    **array;
-    char	    *str;
-    buf_T	    *savebuf;
+    vim_mz_buffer   *buf = NULL;
+    Scheme_Object   *list = NULL;
+    char	    *str = NULL;
     int		    i, n, size;
 
+    MZ_GC_DECL_REG(1);
+    MZ_GC_VAR_IN_REG(0, list);
+    MZ_GC_REG();
+
 #ifdef HAVE_SANDBOX
     sandbox_check();
 #endif
@@ -2206,89 +2465,99 @@
 	check_line_range(n, buf->buf);
     if (SCHEME_STRINGP(list))
     {
-	str = string_to_line(list);
+	buf_T	    *savebuf = curbuf;
 
-	savebuf = curbuf;
+	str = string_to_line(list);
 	curbuf = buf->buf;
 
 	if (u_save((linenr_T)n, (linenr_T)(n+1)) == FAIL)
 	{
 	    curbuf = savebuf;
+	    vim_free(str);
 	    raise_vim_exn(_("cannot save undo information"));
 	}
 	else if (ml_append((linenr_T)n, (char_u *)str, 0, FALSE) == FAIL)
 	{
 	    curbuf = savebuf;
+	    vim_free(str);
 	    raise_vim_exn(_("cannot insert line"));
 	}
 	else
+	{
+	    vim_free(str);
 	    appended_lines_mark((linenr_T)n, 1L);
+	}
 
 	curbuf = savebuf;
 	update_screen(VALID);
 
+	MZ_GC_UNREG();
 	raise_if_error();
 	return scheme_void;
     }
 
     /* List */
     size = scheme_proper_list_length(list);
+    MZ_GC_CHECK();
     if (size < 0)	/* improper or cyclic list */
 	scheme_wrong_type(prim->name, "proper list",
 		2, argc, argv);
-
-    /* Using MzScheme allocator, so we don't need to free this and
-     * can safely keep pointers to GC collected strings
-     */
-    array = (char **)scheme_malloc_fail_ok(
-	    scheme_malloc, (unsigned)(size * sizeof(char *)));
-
-    rest = list;
-    for (i = 0; i < size; ++i)
-    {
-	line = SCHEME_CAR(rest);
-	rest = SCHEME_CDR(rest);
-	array[i] = string_to_line(line);
-    }
-
-    savebuf = curbuf;
-    curbuf = buf->buf;
-
-    if (u_save((linenr_T)n, (linenr_T)(n + 1)) == FAIL)
-    {
-	curbuf = savebuf;
-	raise_vim_exn(_("cannot save undo information"));
-    }
     else
     {
-	for (i = 0; i < size; ++i)
-	    if (ml_append((linenr_T)(n + i), (char_u *)array[i],
-			0, FALSE) == FAIL)
-	    {
-		curbuf = savebuf;
-		raise_vim_exn(_("cannot insert line"));
-	    }
+	Scheme_Object   *line = NULL;
+	Scheme_Object   *rest = NULL;
+	char		**array;
+	buf_T		*savebuf = curbuf;
 
-	if (i > 0)
-	    appended_lines_mark((linenr_T)n, (long)i);
+	MZ_GC_DECL_REG(2);
+	MZ_GC_VAR_IN_REG(0, line);
+	MZ_GC_VAR_IN_REG(1, rest);
+	MZ_GC_REG();
+
+	array = (char **)alloc(size * sizeof(char *));
+	vim_memset(array, 0, size * sizeof(char *));
+
+	rest = list;
+	for (i = 0; i < size; ++i)
+	{
+	    line = SCHEME_CAR(rest);
+	    rest = SCHEME_CDR(rest);
+	    array[i] = string_to_line(line);
+	}
+
+	curbuf = buf->buf;
+
+	if (u_save((linenr_T)n, (linenr_T)(n + 1)) == FAIL)
+	{
+	    curbuf = savebuf;
+	    free_array(array);
+	    raise_vim_exn(_("cannot save undo information"));
+	}
+	else
+	{
+	    for (i = 0; i < size; ++i)
+		if (ml_append((linenr_T)(n + i), (char_u *)array[i],
+			    0, FALSE) == FAIL)
+		{
+		    curbuf = savebuf;
+		    free_array(array);
+		    raise_vim_exn(_("cannot insert line"));
+		}
+
+	    if (i > 0)
+		appended_lines_mark((linenr_T)n, (long)i);
+	}
+	free_array(array);
+	MZ_GC_UNREG();
+	curbuf = savebuf;
+	update_screen(VALID);
     }
 
-    curbuf = savebuf;
-    update_screen(VALID);
-
+    MZ_GC_UNREG();
     raise_if_error();
     return scheme_void;
 }
 
-/* (get-buff-namespace [buffer]) */
-    static Scheme_Object *
-get_buffer_namespace(void *data, int argc, Scheme_Object **argv)
-{
-    Vim_Prim	*prim = (Vim_Prim *)data;
-
-    return (Scheme_Object *)get_buffer_arg(prim->name, 0, argc, argv)->env;
-}
-
 /*
  * Predicates
  */
@@ -2343,41 +2612,173 @@
 /*
  * Convert an MzScheme string into a Vim line.
  *
- * The result is in allocated memory. All internal nulls are replaced by
- * newline characters. It is an error for the string to contain newline
- * characters.
+ * All internal nulls are replaced by newline characters.
+ * It is an error for the string to contain newline characters.
  *
+ * Returns pointer to Vim allocated memory
  */
     static char *
 string_to_line(Scheme_Object *obj)
 {
-    char	*str;
+    char	*scheme_str = NULL;
+    char	*vim_str = NULL;
     long	len;
     int		i;
 
-    str = scheme_display_to_string(obj, &len);
+    scheme_str = scheme_display_to_string(obj, &len);
 
     /* Error checking: String must not contain newlines, as we
      * are replacing a single line, and we must replace it with
      * a single line.
      */
-    if (memchr(str, '\n', len))
+    if (memchr(scheme_str, '\n', len))
 	scheme_signal_error(_("string cannot contain newlines"));
 
+    vim_str = (char *)alloc(len + 1);
+
     /* Create a copy of the string, with internal nulls replaced by
      * newline characters, as is the vim convention.
      */
     for (i = 0; i < len; ++i)
     {
-	if (str[i] == '\0')
-	    str[i] = '\n';
+	if (scheme_str[i] == '\0')
+	    vim_str[i] = '\n';
+	else
+	    vim_str[i] = scheme_str[i];
     }
 
-    str[i] = '\0';
+    vim_str[i] = '\0';
 
-    return str;
+    MZ_GC_CHECK();
+    return vim_str;
 }
 
+#ifdef FEAT_EVAL
+/*
+ * Convert Vim value into MzScheme, adopted from if_python.c
+ */
+    static Scheme_Object *
+vim_to_mzscheme(typval_T *vim_value, int depth, Scheme_Hash_Table *visited)
+{
+    Scheme_Object   *result = NULL;
+    int		    new_value = TRUE;
+
+    MZ_GC_DECL_REG(1);
+    MZ_GC_VAR_IN_REG(0, result);
+    MZ_GC_REG();
+
+    /* Avoid infinite recursion */
+    if (depth > 100)
+    {
+	MZ_GC_UNREG();
+	return scheme_void;
+    }
+
+    /* Check if we run into a recursive loop.  The item must be in visited
+     * then and we can use it again.
+     */
+    result = scheme_hash_get(visited, (Scheme_Object *)vim_value);
+    MZ_GC_CHECK();
+    if (result != NULL) /* found, do nothing */
+	new_value = FALSE;
+    else if (vim_value->v_type == VAR_STRING)
+    {
+	result = scheme_make_string((char *)vim_value->vval.v_string);
+	MZ_GC_CHECK();
+    }
+    else if (vim_value->v_type == VAR_NUMBER)
+    {
+	result = scheme_make_integer((long)vim_value->vval.v_number);
+	MZ_GC_CHECK();
+    }
+# ifdef FEAT_FLOAT
+    else if (vim_value->v_type == VAR_FLOAT)
+    {
+	result = scheme_make_double((double)vim_value->vval.v_float);
+	MZ_GC_CHECK();
+    }
+# endif
+    else if (vim_value->v_type == VAR_LIST)
+    {
+	list_T		*list = vim_value->vval.v_list;
+	listitem_T	*curr;
+
+	if (list == NULL || list->lv_first == NULL)
+	    result = scheme_null;
+	else
+	{
+	    Scheme_Object   *obj = NULL;
+
+	    MZ_GC_DECL_REG(1);
+	    MZ_GC_VAR_IN_REG(0, obj);
+	    MZ_GC_REG();
+
+	    curr = list->lv_last;
+	    obj = vim_to_mzscheme(&curr->li_tv, depth + 1, visited);
+	    result = scheme_make_pair(obj, scheme_null);
+	    MZ_GC_CHECK();
+
+	    while (curr != list->lv_first)
+	    {
+		curr = curr->li_prev;
+		obj = vim_to_mzscheme(&curr->li_tv, depth + 1, visited);
+		result = scheme_make_pair(obj, result);
+		MZ_GC_CHECK();
+	    }
+	}
+	MZ_GC_UNREG();
+    }
+    else if (vim_value->v_type == VAR_DICT)
+    {
+	Scheme_Object	  *key = NULL;
+	Scheme_Object	  *obj = NULL;
+
+	MZ_GC_DECL_REG(2);
+	MZ_GC_VAR_IN_REG(0, key);
+	MZ_GC_VAR_IN_REG(1, obj);
+	MZ_GC_REG();
+
+	result = (Scheme_Object *)scheme_make_hash_table(SCHEME_hash_ptr);
+	MZ_GC_CHECK();
+	if (vim_value->vval.v_dict != NULL)
+	{
+	    hashtab_T	*ht = &vim_value->vval.v_dict->dv_hashtab;
+	    long_u	todo = ht->ht_used;
+	    hashitem_T	*hi;
+	    dictitem_T	*di;
+
+	    for (hi = ht->ht_array; todo > 0; ++hi)
+	    {
+		if (!HASHITEM_EMPTY(hi))
+		{
+		    --todo;
+
+		    di = dict_lookup(hi);
+		    obj = vim_to_mzscheme(&di->di_tv, depth + 1, visited);
+		    key = scheme_make_string((char *)hi->hi_key);
+		    MZ_GC_CHECK();
+		    scheme_hash_set((Scheme_Hash_Table *)result, key, obj);
+		    MZ_GC_CHECK();
+		}
+	    }
+	}
+	MZ_GC_UNREG();
+    }
+    else
+    {
+	result = scheme_void;
+	new_value = FALSE;
+    }
+    if (new_value)
+    {
+	scheme_hash_set(visited, (Scheme_Object *)vim_value, result);
+	MZ_GC_CHECK();
+    }
+    MZ_GC_UNREG();
+    return result;
+}
+#endif
+
 /*
  * Check to see whether a Vim error has been reported, or a keyboard
  * interrupt (from vim --> got_int) has been detected.
@@ -2392,50 +2793,59 @@
  * register Scheme exn:vim
  */
     static void
-register_vim_exn(Scheme_Env *env)
+register_vim_exn(void)
 {
-    Scheme_Object   *exn_name = scheme_intern_symbol("exn:vim");
+    int	nc = 0;
+    int i;
+    Scheme_Object   *struct_exn = NULL;
+    Scheme_Object   *exn_name = NULL;
+
+    MZ_GC_DECL_REG(2);
+    MZ_GC_VAR_IN_REG(0, struct_exn);
+    MZ_GC_VAR_IN_REG(1, exn_name);
+    MZ_GC_REG();
+
+    exn_name = scheme_intern_symbol("exn:vim");
+    MZ_GC_CHECK();
+    struct_exn = scheme_builtin_value("struct:exn");
+    MZ_GC_CHECK();
 
     if (vim_exn == NULL)
 	vim_exn = scheme_make_struct_type(exn_name,
-		scheme_builtin_value("struct:exn"), NULL, 0, 0, NULL, NULL
+		struct_exn, NULL, 0, 0, NULL, NULL
 #if MZSCHEME_VERSION_MAJOR >= 299
 		, NULL
 #endif
 		);
 
-    if (vim_exn_values == NULL)
+
     {
-	int	nc = 0;
+	Scheme_Object   **tmp = NULL;
+	Scheme_Object   *exn_names[5] = {NULL, NULL, NULL, NULL, NULL};
+	Scheme_Object   *exn_values[5] = {NULL, NULL, NULL, NULL, NULL};
+	MZ_GC_DECL_REG(6);
+	MZ_GC_ARRAY_VAR_IN_REG(0, exn_names, 5);
+	MZ_GC_ARRAY_VAR_IN_REG(3, exn_values, 5);
+	MZ_GC_REG();
 
-	Scheme_Object   **exn_names = scheme_make_struct_names(
-		exn_name, scheme_null, 0, &nc);
-	Scheme_Object   **exn_values = scheme_make_struct_values(
-		vim_exn, exn_names, nc, 0);
+	tmp = scheme_make_struct_names(exn_name, scheme_null, 0, &nc);
+	assert(nc <= 5);
+	mch_memmove(exn_names, tmp, nc * sizeof(Scheme_Object *));
+	MZ_GC_CHECK();
 
-	vim_exn_names = scheme_make_vector(nc, scheme_false);
-	vim_exn_values = scheme_make_vector(nc, scheme_false);
-	/* remember names and values */
-	mch_memmove(SCHEME_VEC_ELS(vim_exn_names), exn_names,
-		nc * sizeof(Scheme_Object *));
-	mch_memmove(SCHEME_VEC_ELS(vim_exn_values), exn_values,
-		nc * sizeof(Scheme_Object *));
+	tmp = scheme_make_struct_values(vim_exn, exn_names, nc, 0);
+	mch_memmove(exn_values, tmp, nc * sizeof(Scheme_Object *));
+	MZ_GC_CHECK();
+
+	for (i = 0; i < nc; i++)
+	{
+	    scheme_add_global_symbol(exn_names[i],
+		    exn_values[i], environment);
+	    MZ_GC_CHECK();
+	}
+	MZ_GC_UNREG();
     }
-
-    add_vim_exn(env);
-}
-
-/*
- * Add stuff of exn:vim to env
- */
-    static void
-add_vim_exn(Scheme_Env *env)
-{
-    int i;
-
-    for (i = 0; i < SCHEME_VEC_SIZE(vim_exn_values); i++)
-	scheme_add_global_symbol(SCHEME_VEC_ELS(vim_exn_names)[i],
-		SCHEME_VEC_ELS(vim_exn_values)[i], env);
+    MZ_GC_UNREG();
 }
 
 /*
@@ -2444,26 +2854,54 @@
     void
 raise_vim_exn(const char *add_info)
 {
-    Scheme_Object   *argv[2];
-    char_u	    *fmt = _("Vim error: ~a");
+    char	    *fmt = _("Vim error: ~a");
+    Scheme_Object   *argv[2] = {NULL, NULL};
+    Scheme_Object   *exn = NULL;
+
+    MZ_GC_DECL_REG(4);
+    MZ_GC_ARRAY_VAR_IN_REG(0, argv, 2);
+    MZ_GC_VAR_IN_REG(3, exn);
+    MZ_GC_REG();
 
     if (add_info != NULL)
     {
-	Scheme_Object   *info = scheme_make_string(add_info);
-	argv[0] = scheme_byte_string_to_char_string(scheme_make_string(
-		scheme_format(fmt, strlen(fmt), 1, &info, NULL)));
+	char		*c_string = NULL;
+	Scheme_Object	*byte_string = NULL;
+	Scheme_Object   *info = NULL;
+
+	MZ_GC_DECL_REG(3);
+	MZ_GC_VAR_IN_REG(0, c_string);
+	MZ_GC_VAR_IN_REG(1, byte_string);
+	MZ_GC_VAR_IN_REG(2, info);
+	MZ_GC_REG();
+
+	info = scheme_make_string(add_info);
+	MZ_GC_CHECK();
+	c_string = scheme_format(fmt, STRLEN(fmt), 1, &info, NULL);
+	MZ_GC_CHECK();
+	byte_string = scheme_make_string(c_string);
+	MZ_GC_CHECK();
+	argv[0] = scheme_byte_string_to_char_string(byte_string);
+	MZ_GC_CHECK();
 	SCHEME_SET_IMMUTABLE(argv[0]);
+	MZ_GC_UNREG();
     }
     else
 	argv[0] = scheme_make_string(_("Vim error"));
+    MZ_GC_CHECK();
 
 #if MZSCHEME_VERSION_MAJOR < 360
     argv[1] = scheme_current_continuation_marks();
+    MZ_GC_CHECK();
 #else
     argv[1] = scheme_current_continuation_marks(NULL);
+    MZ_GC_CHECK();
 #endif
 
-    scheme_raise(scheme_make_struct_instance(vim_exn, 2, argv));
+    exn = scheme_make_struct_instance(vim_exn, 2, argv);
+    MZ_GC_CHECK();
+    scheme_raise(exn);
+    MZ_GC_UNREG();
 }
 
     void
@@ -2570,6 +3008,8 @@
 	    curwin->w_cursor.lnum = lo;
 	    check_cursor();
 	}
+	else
+	    check_cursor_col();
 	changed_cline_bef_curs();
     }
     invalidate_botline();
@@ -2595,7 +3035,6 @@
     {mzscheme_open_buffer, "open-buff", 1, 1},
     {get_buffer_by_name, "get-buff-by-name", 1, 1},
     {get_buffer_by_num, "get-buff-by-num", 1, 1},
-    {get_buffer_namespace, "get-buff-namespace", 0, 1},
     /*
      * Window-related commands
      */
@@ -2653,23 +3092,35 @@
 }
 
     static void
-make_modules(Scheme_Env *env)
+make_modules()
 {
-    int		i;
-    Scheme_Env	*mod;
+    int		    i;
+    Scheme_Env	    *mod = NULL;
+    Scheme_Object   *vimext_symbol = NULL;
+    Scheme_Object   *closed_prim = NULL;
 
-    mod = scheme_primitive_module(scheme_intern_symbol("vimext"), env);
+    MZ_GC_DECL_REG(3);
+    MZ_GC_VAR_IN_REG(0, mod);
+    MZ_GC_VAR_IN_REG(1, vimext_symbol);
+    MZ_GC_VAR_IN_REG(2, closed_prim);
+    MZ_GC_REG();
+
+    vimext_symbol = scheme_intern_symbol("vimext");
+    MZ_GC_CHECK();
+    mod = scheme_primitive_module(vimext_symbol, environment);
+    MZ_GC_CHECK();
     /* all prims made closed so they can access their own names */
-    for (i = 0; i < sizeof(prims)/sizeof(prims[0]); i++)
+    for (i = 0; i < (int)(sizeof(prims)/sizeof(prims[0])); i++)
     {
 	Vim_Prim *prim = prims + i;
-	scheme_add_global(prim->name,
-		scheme_make_closed_prim_w_arity(prim->prim, prim, prim->name,
-		    prim->mina, prim->maxa),
-		mod);
+	closed_prim = scheme_make_closed_prim_w_arity(prim->prim, prim, prim->name,
+			    prim->mina, prim->maxa);
+	scheme_add_global(prim->name, closed_prim, mod);
+	MZ_GC_CHECK();
     }
-    scheme_add_global("global-namespace", (Scheme_Object *)environment, mod);
     scheme_finish_primitive_module(mod);
+    MZ_GC_CHECK();
+    MZ_GC_UNREG();
 }
 
 #ifdef HAVE_SANDBOX
@@ -2697,21 +3148,25 @@
 	{
 	    MZ_REGISTER_STATIC(M_write);
 	    M_write = scheme_intern_symbol("write");
+	    MZ_GC_CHECK();
 	}
 	if (M_read == NULL)
 	{
 	    MZ_REGISTER_STATIC(M_read);
 	    M_read = scheme_intern_symbol("read");
+	    MZ_GC_CHECK();
 	}
 	if (M_execute == NULL)
 	{
 	    MZ_REGISTER_STATIC(M_execute);
 	    M_execute = scheme_intern_symbol("execute");
+	    MZ_GC_CHECK();
 	}
 	if (M_delete == NULL)
 	{
 	    MZ_REGISTER_STATIC(M_delete);
 	    M_delete = scheme_intern_symbol("delete");
+	    MZ_GC_CHECK();
 	}
 
 	while (!SCHEME_NULLP(requested_access))
diff --git a/src/if_mzsch.h b/src/if_mzsch.h
index b745cce..4588891 100644
--- a/src/if_mzsch.h
+++ b/src/if_mzsch.h
@@ -11,6 +11,7 @@
 
 /* #ifdef needed for "make depend" */
 #ifdef FEAT_MZSCHEME
+# include <schvers.h>
 # include <scheme.h>
 #endif
 
@@ -46,4 +47,31 @@
 # define scheme_byte_string_to_char_string(obj) (obj)
 #endif
 
+/* Precise GC macros */
+#ifndef MZ_GC_DECL_REG
+# define MZ_GC_DECL_REG(size)            /* empty */
+#endif
+#ifndef MZ_GC_VAR_IN_REG
+# define MZ_GC_VAR_IN_REG(x, v)          /* empty */
+#endif
+#ifndef MZ_GC_ARRAY_VAR_IN_REG
+# define MZ_GC_ARRAY_VAR_IN_REG(x, v, l) /* empty */
+#endif
+#ifndef MZ_GC_REG
+# define MZ_GC_REG()                     /* empty */
+#endif
+#ifndef MZ_GC_UNREG
+# define MZ_GC_UNREG()                   /* empty */
+#endif
+
+#ifdef MZSCHEME_FORCE_GC
+/*
+ * force garbage collection to check all references are registered
+ * seg faults will indicate not registered refs
+ */
+# define MZ_GC_CHECK() scheme_collect_garbage();
+#else
+# define MZ_GC_CHECK()			/* empty */
+#endif
+
 #endif /* _IF_MZSCH_H_ */
diff --git a/src/main.c b/src/main.c
index c0dd121..84aa146 100644
--- a/src/main.c
+++ b/src/main.c
@@ -935,8 +935,14 @@
 
     /*
      * Call the main command loop.  This never returns.
+     * For embedded MzScheme the main_loop will be called by Scheme
+     * for proper stack tracking
      */
+#ifndef FEAT_MZSCHEME
     main_loop(FALSE, FALSE);
+#else
+    mzscheme_main();
+#endif
 
     return 0;
 }
diff --git a/src/proto/if_mzsch.pro b/src/proto/if_mzsch.pro
index 522ac94..f61a087 100644
--- a/src/proto/if_mzsch.pro
+++ b/src/proto/if_mzsch.pro
@@ -15,10 +15,6 @@
 void *mzvim_eval_string __ARGS((char_u *str));
 struct Scheme_Object *mzvim_apply __ARGS((struct Scheme_Object *, int argc,
     struct Scheme_Object **));
-int mzthreads_allowed (void);
-#ifdef FEAT_GUI_KDE
-void timer_proc (void);
-void mzscheme_kde_start_timer (void);
-void mzscheme_kde_stop_timer (void);
-#endif
+int mzthreads_allowed __ARGS((void));
+void mzscheme_main __ARGS((void));
 /* vim: set ft=c : */
diff --git a/src/version.c b/src/version.c
index 7282b6b..52e08a9 100644
--- a/src/version.c
+++ b/src/version.c
@@ -677,6 +677,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    191,
+/**/
     190,
 /**/
     189,