diff --git a/.gitignore b/.gitignore
index e69de29..5e3b114 100644
--- a/.gitignore
+++ b/.gitignore
@@ -0,0 +1,12 @@
+ABOUT-NLS
+**/Makefile.in
+build
+autom4te.cache
+build-aux/
+build/
+configure
+configure~
+aclocal.m4
+m4/*
+!m4/guile.m4
+po
diff --git a/Makefile.am b/Makefile.am
new file mode 100644
index 0000000..9b22ba1
--- /dev/null
+++ b/Makefile.am
@@ -0,0 +1,19 @@
+SUBDIRS = libpetri-guile
+
+EXTRA_DIST = examples pre-inst-env
+
+moddir = $(GUILE_SITE)
+godir = $(GUILE_SITE_CCACHE)
+
+SOURCES = petri.scm
+GOBJECTS = petri.go
+
+mod_DATA = $(SOURCES)
+go_DATA = $(GOBJECTS)
+
+SUFFIXES = .scm .go
+
+GUILE_WARNINGS = -Wunbound-variable -Warity-mismatch -Wformat
+
+.scm.go:
+	$(GUILD) compile $(GUILE_WARNINGS) $(GUILE_TARGET) -o "$@" "$<"
diff --git a/configure.ac b/configure.ac
new file mode 100644
index 0000000..f3d31e7
--- /dev/null
+++ b/configure.ac
@@ -0,0 +1,27 @@
+AC_INIT([petri], [0.1.0])
+AC_CONFIG_SRCDIR([petri.scm])
+AC_CONFIG_AUX_DIR([build-aux])
+AC_CONFIG_MACRO_DIRS([m4])
+
+AM_INIT_AUTOMAKE([-Wall -Werror foreign])
+AM_PROG_AR
+
+LT_INIT([shared disable-static])
+
+AC_PROG_CC
+AC_CONFIG_FILES([
+	Makefile
+	libpetri-guile/Makefile
+])
+AC_CONFIG_FILES([pre-inst-env], [chmod +x pre-inst-env])
+
+GUILE_PKG
+GUILE_PROGS
+GUILE_SITE_DIR
+GUILE_FLAGS
+
+AC_SUBST([GUILE_SITE])
+AC_SUBST([GUILE_SITE_CCACHE])
+AC_SUBST([GUILE_EXTENSION])
+
+AC_OUTPUT
diff --git a/examples/hello-world.scm b/examples/hello-world.scm
new file mode 100644
index 0000000..67e7445
--- /dev/null
+++ b/examples/hello-world.scm
@@ -0,0 +1,9 @@
+(use-modules (petri))
+
+(define (main . args)
+  (init "Hello world!" 0)
+  (let* ([win (make-window)]
+         [label (make-label win "Hello world!")])
+    (window-show win)
+    (event-loop))
+  (quit))
diff --git a/guile-agar/Makefile b/guile-agar/Makefile
deleted file mode 100644
index 6903427..0000000
--- a/guile-agar/Makefile
+++ /dev/null
@@ -1,21 +0,0 @@
-CFLAGS:=`pkg-config --cflags guile-3.0 agar` -I./include/
-LDLIBS:=`pkg-config --libs guile-3.0 agar`
-SRCS:=$(wildcard src/*.c)
-OBJS:=$(SRCS:.c=.o)
-SCMS:=$(patsubst src/%.o,scm/agar/%.scm,$(OBJS))
-OBJS+=$(patsubst scm/agar/%.scm,scm/agar_%_wrap.o,$(SCMS))
-
-.PHONY: driver
-all: libguileagar.so $(SCMS)
-
-clean:
-	rm -rf libguileagar.so $(SCMS) $(OBJS) $(WRAPS)
-
-libguileagar.so: $(OBJS)
-	$(CC) -shared -fPIC -o $@ $^ $(LDLIBS)
-
-scm/agar/%.scm scm/agar_%_wrap.c: scm/%.i include/%.h
-	swig -I./include -guile -Linkage module -scmstub -package agar -o scm/agar_$*_wrap.c scm/$*.i
-
-driver:
-	GUILE_EXTENSIONS_PATH=. guile -L scm driver.scm 
diff --git a/guile-agar/driver.scm b/guile-agar/driver.scm
deleted file mode 100644
index 384572d..0000000
--- a/guile-agar/driver.scm
+++ /dev/null
@@ -1,12 +0,0 @@
-(use-modules (agar core))
-(use-modules (agar gui))
-
-(init-core)
-(init-gui)
-
-(define my-window (make-window))
-(define my-label (make-label my-window))
-(set-label-text my-label "Hi Agar")
-
-(show-window my-window)
-(event-loop)
diff --git a/guile-agar/include/core.h b/guile-agar/include/core.h
deleted file mode 100644
index 404f4dd..0000000
--- a/guile-agar/include/core.h
+++ /dev/null
@@ -1,9 +0,0 @@
-#ifndef __CORE_H__
-#define __CORE_H_
-
-#include <agar/core.h>
-
-void init_core();
-void event_loop();
-
-#endif // __CORE_H__
diff --git a/guile-agar/include/gui.h b/guile-agar/include/gui.h
deleted file mode 100644
index 6c504ee..0000000
--- a/guile-agar/include/gui.h
+++ /dev/null
@@ -1,15 +0,0 @@
-#ifndef __GUI_H__
-#define __GUI_H__
-
-#include <agar/core.h>
-#include <agar/gui.h>
-
-void init_gui();
-
-AG_Window* make_window();
-void show_window(AG_Window*);
-
-AG_Label* make_label(void* parent);
-void set_label_text(AG_Label* label, const char* text);
-
-#endif // __GUI_H__
diff --git a/guile-agar/scm/core.i b/guile-agar/scm/core.i
deleted file mode 100644
index 730e39e..0000000
--- a/guile-agar/scm/core.i
+++ /dev/null
@@ -1,6 +0,0 @@
-%module core
-%scheme %{(load-extension "libguileagar" "scm_init_agar_core_module")%}
-%{
-#include <core.h>
-%}
-%include "core.h"
diff --git a/guile-agar/scm/gui.i b/guile-agar/scm/gui.i
deleted file mode 100644
index fd7ba06..0000000
--- a/guile-agar/scm/gui.i
+++ /dev/null
@@ -1,7 +0,0 @@
-%module gui
-%scheme %{(load-extension "libguileagar" "scm_init_agar_gui_module")%}
-%{
-#include <gui.h>
-%}
-
-%include "gui.h"
diff --git a/guile-agar/src/core.c b/guile-agar/src/core.c
deleted file mode 100644
index c7a7f25..0000000
--- a/guile-agar/src/core.c
+++ /dev/null
@@ -1,9 +0,0 @@
-#include <core.h>
-
-void init_core() {
-  AG_InitCore("agar", 0);
-}
-
-void event_loop() {
-  AG_EventLoop();
-}
diff --git a/guile-agar/src/gui.c b/guile-agar/src/gui.c
deleted file mode 100644
index 3213091..0000000
--- a/guile-agar/src/gui.c
+++ /dev/null
@@ -1,22 +0,0 @@
-#include <gui.h>
-
-void init_gui() {
-  AG_InitGraphics(0);
-}
-
-AG_Window *make_window() {
-  return AG_WindowNew(AG_WINDOW_MAIN);
-}
-
-void show_window(AG_Window *win) {
-  AG_WindowShow(win);
-}
-
-AG_Label* make_label(void* parent) {
-  return AG_LabelNew(parent, 0, "");
-}
-
-void set_label_text(AG_Label* label, const char* text) {
-  AG_LabelText(label, text);
-}
-
diff --git a/libpetri-guile/Makefile.am b/libpetri-guile/Makefile.am
new file mode 100644
index 0000000..f9a99b6
--- /dev/null
+++ b/libpetri-guile/Makefile.am
@@ -0,0 +1,12 @@
+SUFFIXES = .x
+
+extensiondir = $(GUILE_EXTENSION)
+extension_LTLIBRARIES = libpetri-guile.la
+
+libpetri_guile_la_SOURCES = petri.c
+libpetri_guile_la_CFLAGS = `pkg-config --cflags guile-3.0 agar`
+libpetri_guile_la_LDFLAGS = `pkg-config --libs guile-3.0 agar`
+BUILT_SOURCES = petri.x
+
+petri.x: petri.c
+	guile-snarf -o $@ $< $(libpetri_guile_la_CFLAGS)
diff --git a/libpetri-guile/petri.c b/libpetri-guile/petri.c
new file mode 100644
index 0000000..329eff4
--- /dev/null
+++ b/libpetri-guile/petri.c
@@ -0,0 +1,58 @@
+#include <agar/core.h>
+#include <agar/gui.h>
+#include <libguile.h>
+
+SCM_DEFINE(init, "init", 2, 0, 0,
+	   (SCM name, SCM flags), "Initialize Agar's core functionality")
+{
+  AG_InitCore(scm_to_locale_string(name), scm_to_uint(flags));
+  return scm_from_uint(AG_InitGraphics(NULL));
+}
+
+SCM_DEFINE(get_error, "get-error", 0, 0, 0,
+	   (), "Return the last error message")
+{
+  const char *err = AG_GetError();
+  return scm_from_locale_string(err);
+}
+
+SCM_DEFINE(quit, "quit", 0, 0, 0,
+	   (), "Shutdown Petri")
+{
+  AG_Destroy();
+  AG_Quit();
+  return SCM_UNDEFINED;
+}
+
+SCM_DEFINE(event_loop, "event-loop", 0, 0, 0,
+	   (), "")
+{
+  AG_EventLoop();
+  return SCM_UNDEFINED;
+}
+
+SCM_DEFINE(window_new, "_window-new", 0, 0, 0,
+	   (), "Create a new base level container")
+{
+  return scm_from_pointer(AG_WindowNew(AG_WINDOW_MAIN), AG_ObjectDestroy);
+}
+
+SCM_DEFINE(window_show, "window-show", 1, 0, 0,
+	   (SCM win), "Display a window")
+{
+  AG_WindowShow(scm_to_pointer(win));
+  return SCM_UNDEFINED;
+}
+
+SCM_DEFINE(label_new, "_label-new", 2, 0, 0,
+	   (SCM parent, SCM text), "Create a new label with text")
+{
+  return scm_from_pointer(AG_LabelNew(scm_to_pointer(parent), 0, scm_to_locale_string(text)), AG_ObjectDestroy);
+}
+
+void
+init_petri() {
+  #ifndef SCM_MAGIC_SNARFER
+  #include "petri.x"
+  #endif
+}
diff --git a/m4/guile.m4 b/m4/guile.m4
new file mode 100644
index 0000000..ea01f5a
--- /dev/null
+++ b/m4/guile.m4
@@ -0,0 +1,395 @@
+## Autoconf macros for working with Guile.
+##
+##   Copyright (C) 1998, 2001, 2006, 2010, 2012, 2013, 2014, 2020, 2025 Free Software Foundation, Inc.
+##
+## This library is free software; you can redistribute it and/or
+## modify it under the terms of the GNU Lesser General Public License
+## as published by the Free Software Foundation; either version 3 of
+## the License, or (at your option) any later version.
+##
+## This library is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+## Lesser General Public License for more details.
+##
+## You should have received a copy of the GNU Lesser General Public License
+## along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+# serial 11
+
+## Index
+## -----
+##
+## GUILE_PKG -- find Guile development files
+## GUILE_PROGS -- set paths to Guile interpreter, config and tool programs
+## GUILE_FLAGS -- set flags for compiling and linking with Guile
+## GUILE_SITE_DIR -- find path to Guile "site" directories
+## GUILE_CHECK -- evaluate Guile Scheme code and capture the return value
+## GUILE_MODULE_CHECK -- check feature of a Guile Scheme module
+## GUILE_MODULE_AVAILABLE -- check availability of a Guile Scheme module
+## GUILE_MODULE_REQUIRED -- fail if a Guile Scheme module is unavailable
+## GUILE_MODULE_EXPORTS -- check if a module exports a variable
+## GUILE_MODULE_REQUIRED_EXPORT -- fail if a module doesn't export a variable
+
+## Code
+## ----
+
+## NOTE: Comments preceding an AC_DEFUN (starting from "Usage:") are massaged
+## into doc/ref/autoconf-macros.texi (see Makefile.am in that directory).
+
+# GUILE_PKG -- find Guile development files
+#
+# Usage: GUILE_PKG([VERSIONS])
+#
+# This macro runs the @code{pkg-config} tool to find development files
+# for an available version of Guile.
+#
+# By default, this macro will search for the latest stable version of
+# Guile (e.g. 3.0), falling back to the previous stable version
+# (e.g. 2.2) if it is available.  If no guile-@var{VERSION}.pc file is
+# found, an error is signaled.  The found version is stored in
+# @var{GUILE_EFFECTIVE_VERSION}.
+#
+# If @code{GUILE_PROGS} was already invoked, this macro ensures that the
+# development files have the same effective version as the Guile
+# program.
+#
+# @var{GUILE_EFFECTIVE_VERSION} is marked for substitution, as by
+# @code{AC_SUBST}.
+#
+AC_DEFUN([GUILE_PKG],
+ [AC_REQUIRE([PKG_PROG_PKG_CONFIG])
+  if test "x$PKG_CONFIG" = x; then
+    AC_MSG_ERROR([pkg-config is missing, please install it])
+  fi
+  _guile_versions_to_search="m4_default([$1], [3.0 2.2 2.0])"
+  if test -n "$GUILE_EFFECTIVE_VERSION"; then
+    _guile_tmp=""
+    for v in $_guile_versions_to_search; do
+      if test "$v" = "$GUILE_EFFECTIVE_VERSION"; then
+        _guile_tmp=$v
+      fi
+    done
+    if test -z "$_guile_tmp"; then
+      AC_MSG_FAILURE([searching for guile development files for versions $_guile_versions_to_search, but previously found $GUILE version $GUILE_EFFECTIVE_VERSION])
+    fi
+    _guile_versions_to_search=$GUILE_EFFECTIVE_VERSION
+  fi
+  GUILE_EFFECTIVE_VERSION=""
+  _guile_errors=""
+  for v in $_guile_versions_to_search; do
+    if test -z "$GUILE_EFFECTIVE_VERSION"; then
+      AC_MSG_NOTICE([checking for guile $v])
+      PKG_CHECK_EXISTS([guile-$v], [GUILE_EFFECTIVE_VERSION=$v], [])
+    fi
+  done
+
+  if test -z "$GUILE_EFFECTIVE_VERSION"; then
+    AC_MSG_ERROR([
+No Guile development packages were found.
+
+Please verify that you have Guile installed.  If you installed Guile
+from a binary distribution, please verify that you have also installed
+the development packages.  If you installed it yourself, you might need
+to adjust your PKG_CONFIG_PATH; see the pkg-config man page for more.
+])
+  fi
+  AC_MSG_NOTICE([found guile $GUILE_EFFECTIVE_VERSION])
+  AC_SUBST([GUILE_EFFECTIVE_VERSION])
+ ])
+
+# GUILE_FLAGS -- set flags for compiling and linking with Guile
+#
+# Usage: GUILE_FLAGS
+#
+# This macro runs the @code{pkg-config} tool to find out how to compile
+# and link programs against Guile.  It sets four variables:
+# @var{GUILE_CFLAGS}, @var{GUILE_LDFLAGS}, @var{GUILE_LIBS}, and
+# @var{GUILE_LTLIBS}.
+#
+# @var{GUILE_CFLAGS}: flags to pass to a C or C++ compiler to build code that
+# uses Guile header files.  This is almost always just one or more @code{-I}
+# flags.
+#
+# @var{GUILE_LDFLAGS}: flags to pass to the compiler to link a program
+# against Guile.  This includes @code{-lguile-@var{VERSION}} for the
+# Guile library itself, and may also include one or more @code{-L} flag
+# to tell the compiler where to find the libraries.  But it does not
+# include flags that influence the program's runtime search path for
+# libraries, and will therefore lead to a program that fails to start,
+# unless all necessary libraries are installed in a standard location
+# such as @file{/usr/lib}.
+#
+# @var{GUILE_LIBS} and @var{GUILE_LTLIBS}: flags to pass to the compiler or to
+# libtool, respectively, to link a program against Guile.  It includes flags
+# that augment the program's runtime search path for libraries, so that shared
+# libraries will be found at the location where they were during linking, even
+# in non-standard locations.  @var{GUILE_LIBS} is to be used when linking the
+# program directly with the compiler, whereas @var{GUILE_LTLIBS} is to be used
+# when linking the program is done through libtool.
+#
+# The variables are marked for substitution, as by @code{AC_SUBST}.
+#
+AC_DEFUN([GUILE_FLAGS],
+ [AC_REQUIRE([GUILE_PKG])
+  PKG_CHECK_MODULES(GUILE, [guile-$GUILE_EFFECTIVE_VERSION])
+
+  dnl GUILE_CFLAGS and GUILE_LIBS are already defined and AC_SUBST'd by
+  dnl PKG_CHECK_MODULES.  But GUILE_LIBS to pkg-config is GUILE_LDFLAGS
+  dnl to us.
+
+  GUILE_LDFLAGS=$GUILE_LIBS
+
+  dnl Determine the platform dependent parameters needed to use rpath.
+  dnl AC_LIB_LINKFLAGS_FROM_LIBS is defined in gnulib/m4/lib-link.m4 and needs
+  dnl the file gnulib/build-aux/config.rpath.
+  AC_LIB_LINKFLAGS_FROM_LIBS([GUILE_LIBS], [$GUILE_LDFLAGS], [])
+  GUILE_LIBS="$GUILE_LDFLAGS $GUILE_LIBS"
+  AC_LIB_LINKFLAGS_FROM_LIBS([GUILE_LTLIBS], [$GUILE_LDFLAGS], [yes])
+  GUILE_LTLIBS="$GUILE_LDFLAGS $GUILE_LTLIBS"
+
+  AC_SUBST([GUILE_EFFECTIVE_VERSION])
+  AC_SUBST([GUILE_CFLAGS])
+  AC_SUBST([GUILE_LDFLAGS])
+  AC_SUBST([GUILE_LIBS])
+  AC_SUBST([GUILE_LTLIBS])
+ ])
+
+# GUILE_SITE_DIR -- find path to Guile site directories
+#
+# Usage: GUILE_SITE_DIR
+#
+# This looks for Guile's "site" directories.  The variable @var{GUILE_SITE} will
+# be set to Guile's "site" directory for Scheme source files (usually something
+# like PREFIX/share/guile/site).  @var{GUILE_SITE_CCACHE} will be set to the
+# directory for compiled Scheme files also known as @code{.go} files
+# (usually something like
+# PREFIX/lib/guile/@var{GUILE_EFFECTIVE_VERSION}/site-ccache).
+# @var{GUILE_EXTENSION} will be set to the directory for compiled C extensions
+# (usually something like
+# PREFIX/lib/guile/@var{GUILE_EFFECTIVE_VERSION}/extensions). The latter two
+# are set to blank if the particular version of Guile does not support
+# them.  Note that this macro will run the macros @code{GUILE_PKG} and
+# @code{GUILE_PROGS} if they have not already been run.
+#
+# The variables are marked for substitution, as by @code{AC_SUBST}.
+#
+AC_DEFUN([GUILE_SITE_DIR],
+ [AC_REQUIRE([GUILE_PKG])
+  AC_REQUIRE([GUILE_PROGS])
+  AC_MSG_CHECKING(for Guile site directory)
+  GUILE_SITE=`$PKG_CONFIG --print-errors --variable=sitedir guile-$GUILE_EFFECTIVE_VERSION`
+  AC_MSG_RESULT($GUILE_SITE)
+  if test "$GUILE_SITE" = ""; then
+     AC_MSG_FAILURE(sitedir not found)
+  fi
+  AC_SUBST(GUILE_SITE)
+  AC_MSG_CHECKING([for Guile site-ccache directory using pkgconfig])
+  GUILE_SITE_CCACHE=`$PKG_CONFIG --variable=siteccachedir guile-$GUILE_EFFECTIVE_VERSION`
+  if test "$GUILE_SITE_CCACHE" = ""; then
+    AC_MSG_RESULT(no)
+    AC_MSG_CHECKING([for Guile site-ccache directory using interpreter])
+    GUILE_SITE_CCACHE=`$GUILE -c "(display (if (defined? '%site-ccache-dir) (%site-ccache-dir) \"\"))"`
+    if test $? != "0" -o "$GUILE_SITE_CCACHE" = ""; then
+      AC_MSG_RESULT(no)
+      GUILE_SITE_CCACHE=""
+      AC_MSG_WARN([siteccachedir not found])
+    fi
+  fi
+  AC_MSG_RESULT($GUILE_SITE_CCACHE)
+  AC_SUBST([GUILE_SITE_CCACHE])
+  AC_MSG_CHECKING(for Guile extensions directory)
+  GUILE_EXTENSION=`$PKG_CONFIG --print-errors --variable=extensiondir guile-$GUILE_EFFECTIVE_VERSION`
+  AC_MSG_RESULT($GUILE_EXTENSION)
+  if test "$GUILE_EXTENSION" = ""; then
+    GUILE_EXTENSION=""
+    AC_MSG_WARN(extensiondir not found)
+  fi
+  AC_SUBST(GUILE_EXTENSION)
+ ])
+
+# GUILE_PROGS -- set paths to Guile interpreter, config and tool programs
+#
+# Usage: GUILE_PROGS([VERSION])
+#
+# This macro looks for programs @code{guile} and @code{guild}, setting
+# variables @var{GUILE} and @var{GUILD} to their paths, respectively.
+# The macro will attempt to find @code{guile} with the suffix of
+# @code{-X.Y}, followed by looking for it with the suffix @code{X.Y}, and
+# then fall back to looking for @code{guile} with no suffix. If
+# @code{guile} is still not found, signal an error. The suffix, if any,
+# that was required to find @code{guile} will be used for @code{guild}
+# as well.
+#
+# By default, this macro will search for the latest stable version of
+# Guile (e.g. 3.0). x.y or x.y.z versions can be specified. If an older
+# version is found, the macro will signal an error.
+#
+# The effective version of the found @code{guile} is set to
+# @var{GUILE_EFFECTIVE_VERSION}.  This macro ensures that the effective
+# version is compatible with the result of a previous invocation of
+# @code{GUILE_FLAGS}, if any.
+#
+# As a legacy interface, it also looks for @code{guile-config} and
+# @code{guile-tools}, setting @var{GUILE_CONFIG} and @var{GUILE_TOOLS}.
+#
+# The variables are marked for substitution, as by @code{AC_SUBST}.
+#
+AC_DEFUN([GUILE_PROGS],
+ [_guile_required_version="m4_default([$1], [$GUILE_EFFECTIVE_VERSION])"
+  if test -z "$_guile_required_version"; then
+    _guile_required_version=3.0
+  fi
+
+  _guile_candidates=guile
+  _tmp=
+  for v in `echo "$_guile_required_version" | tr . ' '`; do
+    if test -n "$_tmp"; then _tmp=$_tmp.; fi
+    _tmp=$_tmp$v
+    _guile_candidates="guile-$_tmp guile$_tmp $_guile_candidates"
+  done
+
+  AC_PATH_PROGS(GUILE,[$_guile_candidates])
+  if test -z "$GUILE"; then
+      AC_MSG_ERROR([guile required but not found])
+  fi
+
+  _guile_suffix=`echo "$GUILE" | sed -e 's,^.*/guile\(.*\)$,\1,'`
+  _guile_effective_version=`$GUILE -c "(display (effective-version))"`
+  if test -z "$GUILE_EFFECTIVE_VERSION"; then
+    GUILE_EFFECTIVE_VERSION=$_guile_effective_version
+  elif test "$GUILE_EFFECTIVE_VERSION" != "$_guile_effective_version"; then
+    AC_MSG_ERROR([found development files for Guile $GUILE_EFFECTIVE_VERSION, but $GUILE has effective version $_guile_effective_version])
+  fi
+
+  _guile_major_version=`$GUILE -c "(display (major-version))"`
+  _guile_minor_version=`$GUILE -c "(display (minor-version))"`
+  _guile_micro_version=`$GUILE -c "(display (micro-version))"`
+  _guile_prog_version="$_guile_major_version.$_guile_minor_version.$_guile_micro_version"
+
+  AC_MSG_CHECKING([for Guile version >= $_guile_required_version])
+  _major_version=`echo $_guile_required_version | cut -d . -f 1`
+  _minor_version=`echo $_guile_required_version | cut -d . -f 2`
+  _micro_version=`echo $_guile_required_version | cut -d . -f 3`
+  if test "$_guile_major_version" -gt "$_major_version"; then
+    true
+  elif test "$_guile_major_version" -eq "$_major_version"; then
+    if test "$_guile_minor_version" -gt "$_minor_version"; then
+      true
+    elif test "$_guile_minor_version" -eq "$_minor_version"; then
+      if test -n "$_micro_version"; then
+        if test "$_guile_micro_version" -lt "$_micro_version"; then
+          AC_MSG_ERROR([Guile $_guile_required_version required, but $_guile_prog_version found])
+        fi
+      fi
+    elif test "$GUILE_EFFECTIVE_VERSION" = "$_major_version.$_minor_version" -a -z "$_micro_version"; then
+      # Allow prereleases that have the right effective version.
+      true
+    else
+      as_fn_error $? "Guile $_guile_required_version required, but $_guile_prog_version found" "$LINENO" 5
+    fi
+  elif test "$GUILE_EFFECTIVE_VERSION" = "$_major_version.$_minor_version" -a -z "$_micro_version"; then
+    # Allow prereleases that have the right effective version.
+    true
+  else
+    AC_MSG_ERROR([Guile $_guile_required_version required, but $_guile_prog_version found])
+  fi
+  AC_MSG_RESULT([$_guile_prog_version])
+
+  AC_PATH_PROG(GUILD,[guild$_guile_suffix])
+  AC_SUBST(GUILD)
+
+  AC_PATH_PROG(GUILE_CONFIG,[guile-config$_guile_suffix])
+  AC_SUBST(GUILE_CONFIG)
+  if test -n "$GUILD"; then
+    GUILE_TOOLS=$GUILD
+  else
+    AC_PATH_PROG(GUILE_TOOLS,[guile-tools$_guile_suffix])
+  fi
+  AC_SUBST(GUILE_TOOLS)
+ ])
+
+# GUILE_CHECK -- evaluate Guile Scheme code and capture the return value
+#
+# Usage: GUILE_CHECK_RETVAL(var,check)
+#
+# @var{var} is a shell variable name to be set to the return value.
+# @var{check} is a Guile Scheme expression, evaluated with "$GUILE -c", and
+#    returning either 0 or non-#f to indicate the check passed.
+#    Non-0 number or #f indicates failure.
+#    Avoid using the character "#" since that confuses autoconf.
+#
+AC_DEFUN([GUILE_CHECK],
+ [AC_REQUIRE([GUILE_PROGS])
+  $GUILE -c "$2" > /dev/null 2>&1
+  $1=$?
+ ])
+
+# GUILE_MODULE_CHECK -- check feature of a Guile Scheme module
+#
+# Usage: GUILE_MODULE_CHECK(var,module,featuretest,description)
+#
+# @var{var} is a shell variable name to be set to "yes" or "no".
+# @var{module} is a list of symbols, like: (ice-9 common-list).
+# @var{featuretest} is an expression acceptable to GUILE_CHECK, q.v.
+# @var{description} is a present-tense verb phrase (passed to AC_MSG_CHECKING).
+#
+AC_DEFUN([GUILE_MODULE_CHECK],
+         [AC_MSG_CHECKING([if $2 $4])
+	  GUILE_CHECK($1,(use-modules $2) (exit ((lambda () $3))))
+	  if test "$$1" = "0" ; then $1=yes ; else $1=no ; fi
+          AC_MSG_RESULT($$1)
+         ])
+
+# GUILE_MODULE_AVAILABLE -- check availability of a Guile Scheme module
+#
+# Usage: GUILE_MODULE_AVAILABLE(var,module)
+#
+# @var{var} is a shell variable name to be set to "yes" or "no".
+# @var{module} is a list of symbols, like: (ice-9 common-list).
+#
+AC_DEFUN([GUILE_MODULE_AVAILABLE],
+         [GUILE_MODULE_CHECK($1,$2,0,is available)
+         ])
+
+# GUILE_MODULE_REQUIRED -- fail if a Guile Scheme module is unavailable
+#
+# Usage: GUILE_MODULE_REQUIRED(symlist)
+#
+# @var{symlist} is a list of symbols, WITHOUT surrounding parens,
+# like: ice-9 common-list.
+#
+AC_DEFUN([GUILE_MODULE_REQUIRED],
+         [GUILE_MODULE_AVAILABLE(ac_guile_module_required, ($1))
+          if test "$ac_guile_module_required" = "no" ; then
+              AC_MSG_ERROR([required guile module not found: ($1)])
+          fi
+         ])
+
+# GUILE_MODULE_EXPORTS -- check if a module exports a variable
+#
+# Usage: GUILE_MODULE_EXPORTS(var,module,modvar)
+#
+# @var{var} is a shell variable to be set to "yes" or "no".
+# @var{module} is a list of symbols, like: (ice-9 common-list).
+# @var{modvar} is the Guile Scheme variable to check.
+#
+AC_DEFUN([GUILE_MODULE_EXPORTS],
+ [GUILE_MODULE_CHECK($1,$2,$3,exports `$3')
+ ])
+
+# GUILE_MODULE_REQUIRED_EXPORT -- fail if a module doesn't export a variable
+#
+# Usage: GUILE_MODULE_REQUIRED_EXPORT(module,modvar)
+#
+# @var{module} is a list of symbols, like: (ice-9 common-list).
+# @var{modvar} is the Guile Scheme variable to check.
+#
+AC_DEFUN([GUILE_MODULE_REQUIRED_EXPORT],
+ [GUILE_MODULE_EXPORTS(guile_module_required_export,$1,$2)
+  if test "$guile_module_required_export" = "no" ; then
+      AC_MSG_ERROR([module $1 does not export $2; required])
+  fi
+ ])
+
+## guile.m4 ends here
diff --git a/petri.scm b/petri.scm
index 46a7dc5..e5388bc 100644
--- a/petri.scm
+++ b/petri.scm
@@ -1,11 +1,12 @@
 (define-module (petri)
-  :use-module (agar core)
-  :use-module (agar gui)
-  :export (petri-app))
+  #:use-module (ice-9 format)
+  #:export (init get-error event-loop make-window make-label window-show)
+  #:replace (quit))
 
-(define-syntax-rule (petri-app exp ...)
-  (begin
-    (init-core)
-    (init-gui)
-    exp ...
-    (event-loop)))
+(load-extension "libpetri-guile" "init_petri")
+
+(define (make-window)
+  (_window-new))
+
+(define (make-label parent fmt . args)
+  (_label-new parent (apply format #f fmt args)))
diff --git a/pre-inst-env.in b/pre-inst-env.in
new file mode 100644
index 0000000..e8bab7b
--- /dev/null
+++ b/pre-inst-env.in
@@ -0,0 +1,12 @@
+#!/bin/sh
+
+abs_top_srcdir="@abs_top_srcdir@"
+abs_top_builddir="@abs_top_builddir@"
+
+GUILE_LOAD_PATH="$abs_top_srcdir"
+GUILE_LOAD_COMPILED_PATH="$abs_top_builddir"
+GUILE_EXTENSIONS_PATH="$abs_top_builddir/libpetri-guile/.libs"
+
+export GUILE_LOAD_PATH GUILE_LOAD_COMPILED_PATH GUILE_EXTENSIONS_PATH
+
+exec "$@"