diff --git a/Formula/gap.rb b/Formula/gap.rb
index a11bdb4..74b2ef5 100644
--- a/Formula/gap.rb
+++ b/Formula/gap.rb
@@ -3,6 +3,13 @@ class Gap < Formula
   homepage "https://www.gap-system.org/"
   url "https://github.com/gap-system/gap/releases/download/v4.13.0/gap-4.13.0.tar.gz"
   sha256 "cc76ecbe33d6719450a593e613fb87e9e4247faa876f632dd0f97c398f92265d"
+  license "GPL-2.0-or-later"
+
+
+  head do
+    url "https://github.com/gap-system/gap.git", branch: "master"
+    depends_on "autoconf" => :build # required by packages below
+  end
 
   depends_on "gmp"
   # GAP cannot be built against the native macOS version of readline
@@ -11,41 +18,121 @@ class Gap < Formula
   # So we depend on GNU readline here.
   depends_on "readline"
 
+  # for packages
+  depends_on "cddlib"   # CddInterface
+  depends_on "curl"     # curlInterface
+  depends_on "fplll"    # float
+  depends_on "libmpc"   # float
+  depends_on "mpfi"     # float
+  depends_on "mpfr"     # float, normalizinterface
+  depends_on "ncurses"  # browse
+  depends_on "zeromq"   # ZeroMQInterface
+  depends_on "singular" # many packages
+  depends_on "pari"     # many packages
+
   def install
-    # XXX:  Currently there is no `install` target in `Makefile`.
-    #   According to the manual installation instructions in
-    #
-    #     https://github.com/gap-system/gap/blob/master/INSTALL.md
-    #
-    #   the compiled "bundle" is intended to be used "as is," and there is
-    #   no instructions for how to remove the source and other unnecessary
-    #   files after compilation.  Moreover, the content of the
-    #   subdirectories with special names, such as `bin` and `lib`, is not
-    #   suitable for merging with the content of the corresponding
-    #   subdirectories of `/usr/local`.  The easiest temporary solution seems
-    #   to be to drop the compiled bundle into `<prefix>/libexec` and to
-    #   create a symlink `<prefix>/bin/gap` to the startup script.
-    #   This use of `libexec` seems to contradict Linux Filesystem Hierarchy
-    #   Standard, but is recommended in Homebrew's "Formula Cookbook."
-
-    libexec.install Dir["*"]
-
-    # GAP does not support "make install" so it has to be compiled in place
-
-    cd libexec do
-      system "./configure", "--with-readline=#{Formula["readline"].opt_prefix}"
-      system "make"
+
+
+    no_compilation_packages = [
+      "atlasrep", "aclib", "agt", "alnuth", "automata", "automgrp",
+      "autpgrp", "circle", "classicpres", "congruence", "corelg",
+      "crime", "crisp", "cryst", "crystcat", "ctbllib", "cubefree",
+      "design", "difsets", "factint", "fga", "fining", "format",
+      "forms", "fr", "francy", "fwtree", "gapdoc", "gbnp", "genss",
+      "groupoids", "grpconst", "guarana", "hap", "hapcryst", "hecke",
+      "help", "idrel", "images", "intpic", "irredsol", "itc",
+      "jupyterkernel", "jupyterviz", "kan", "laguna", "liealgdb",
+      "liepring", "liering", "loops", "lpres", "majoranaalgebras",
+      "mapclass", "matgrp", "modisom", "nilmat", "nock",
+      "numericalsgps", "openmath", "packagemanager", "patternclass",
+      "permut", "polenta", "polycyclic", "polymaking", "primgrp",
+      "qpa", "quagroup", "radiroot", "rcwa", "rds", "recog",
+      "repndecomp", "repsn", "resclasses", "scscp", "sglppow",
+      "sgpviz", "singular", "sl2reps", "sla", "smallgrp", "smallsemi",
+      "sonata", "sophus", "spinsym", "standardff", "symbcompcc",
+      "thelma", "tomlib", "toric", "transgrp", "ugaly", "unipot",
+      "unitlib", "utils", "uuid", "walrus", "wedderga", "xmod",
+      "xmodalg", "yangbaxter",
+      # These packages have `doc` and `test` make targets, but we
+      # don't actually call them
+      "4ti2interface", "autodoc", "cap", "examplesforhomalg",
+      "gaussforhomalg", "generalizedmorphismsforcap", "gradedmodules",
+      "gradedringforhomalg", "homalg", "homalgtocas", "io_forhomalg",
+      "linearalgebraforcap", "localizeringforhomalg",
+      "matricesforhomalg", "modulepresentationsforcap", "modules",
+      "monoidalcategories", "nconvex", "ringsforhomalg", "sco",
+      "toolsforhomalg", "toricvarieties",
+    ]
+
+    # These two packages either don't build or don't work
+    # "cddinterface", "xgap",
+    configure_packages = [
+      "anupq", "caratinterface", "crypting", "curlinterface", "cvec",
+      "datastructures", "deepthought", "digraphs", "ferret", "float",
+      "gauss", "grape", "io", "json", "normalizinterface", "nq",
+      "orb", "profiling", "semigroups", "simpcomp", "zeromqinterface",
+      ]
+
+    old_configure_packages = [
+      "ace", "browse", "cohomolo", "edim", "example", "fplsa",
+      "guava", "kbmag",
+    ]
+
+
+
+    all_packages = no_compilation_packages
+                     .concat(configure_packages)
+                     .concat(configure_packages)
+
+    # Start actually building GAP
+    if build.head?
+      system "./autogen.sh"
+    end
+
+    libexec.install Dir["pkg"]
+
+    system "./configure", "--prefix", libexec/"gap", "--with-readline=#{Formula["readline"].opt_prefix}"
+    if build.head?
+      system "make", "bootstrap-pkg-full"
+      # system "make", "doc"      # Do we need this?
     end
+    system "make", "install"
 
     # Create a symlink `bin/gap` from the `gap` binary
-    bin.install_symlink libexec/"gap" => "gap"
+    bin.install_symlink libexec/"gap/bin/gap" => "gap"
 
     ohai "Building included packages. Please be patient, it may take a while"
+    pkg_dir = "#{libexec}/pkg"
+
     cd libexec/"pkg" do
-      # NOTE: This script will build most of the packages that require
-      # compilation. It is known to produce a number of warnings and
-      # error messages, possibly failing to build several packages.
-      system "../bin/BuildPackages.sh", "--with-gaproot=#{libexec}"
+
+      system "mkdir", "#{libexec}/gap/lib/gap/pkg/"
+
+      # The makefiles appear to only be used for docs...
+      # The BuildPackages.sh script didn't call them
+      all_packages.each do |pkg|
+        system "cp", "-R", pkg, "#{libexec}/gap/lib/gap/pkg/"
+        cd pkg do
+          if File.exist?("./prerequisites.sh")
+            system "./prerequisites.sh", "#{libexec}/gap/lib/gap"
+          end
+        end
+      end
+
+      configure_packages.each do |pkg|
+        cd pkg do
+          system "./configure", "--with-gaproot=#{libexec}/gap/lib/gap"
+          system "make"
+          system "cp", "-R", "bin/", "#{libexec}/gap/lib/gap/pkg/#{pkg}"
+        end
+      end
+      old_configure_packages.each do |pkg|
+        cd pkg do
+          system "./configure", "#{libexec}/gap/lib/gap"
+          system "make"
+          system "cp", "-R", "bin/", "#{libexec}/gap/lib/gap/pkg/#{pkg}"
+        end
+      end
     end
   end
 
@@ -53,4 +140,5 @@ def install
     ENV["LC_CTYPE"] = "en_GB.UTF-8"
     system bin/"gap", "-r", "-A", "#{libexec}/tst/testinstall.g"
   end
+
 end