diff --git a/lib/build.ml b/lib/build.ml
new file mode 100644
index 0000000..240f108
--- /dev/null
+++ b/lib/build.ml
@@ -0,0 +1,142 @@
+open Types
+
+let sanitize s =
+  String.concat "/" (List.map (fun p -> if p = ".." then "__" else p) (String.split_on_char '/' s))
+
+let obj_of p (t : target) src = p.tc.builddir ^ "/obj/" ^ t.name ^ "/" ^ sanitize src ^ ".o"
+let lib_of p (t : target) = p.tc.builddir ^ "/lib" ^ t.name ^ ".a"
+let dylib_ext p = if p.platform = "darwin" then ".dylib" else ".so"
+let so_of p (t : target) = p.tc.builddir ^ "/lib" ^ t.name ^ dylib_ext p
+let bin_of p (t : target) = p.tc.builddir ^ "/bin/" ^ t.name
+let test_of p (t : target) = p.tc.builddir ^ "/test/" ^ t.name
+
+let out_of p (t : target) =
+  match t.kind with
+  | Lib -> lib_of p t
+  | Shared -> so_of p t
+  | Bin -> bin_of p t
+  | Test -> test_of p t
+
+let pic_set p =
+  let set = Hashtbl.create 8 in
+  List.iter
+    (fun t ->
+      if t.kind = Shared then begin
+        Hashtbl.replace set t.name ();
+        List.iter (fun (d : target) -> Hashtbl.replace set d.name ()) (deps_of p t)
+      end)
+    p.targets;
+  set
+
+let config_dir p = match p.config_header with None -> [] | Some h -> [ Filename.dirname h ]
+
+let includes_of p (t : target) =
+  let inherited = List.concat_map (fun (d : target) -> d.includes) (deps_of p t) in
+  List.sort_uniq compare (t.includes @ inherited @ config_dir p)
+
+let compile_cmd p ~pic (t : target) src obj =
+  let lang = lang_of src in
+  let driver = match lang with Cxx -> p.tc.cxx | _ -> p.tc.cc in
+  let base = match lang with Cxx -> p.tc.cxxflags @ t.cxxflags | _ -> p.tc.cflags @ t.cflags in
+  let inherited_flags =
+    List.concat_map
+      (fun (d : target) -> match lang with Cxx -> d.cxxflags | _ -> d.cflags)
+      (deps_of p t)
+    |> List.filter (fun f -> String.length f > 1 && String.sub f 0 2 = "-I")
+  in
+  let flags =
+    base @ inherited_flags
+    @ (if Hashtbl.mem pic t.name then [ "-fPIC" ] else [])
+    @ List.concat_map (fun d -> [ "-D"; d ]) t.defines
+    @ List.concat_map (fun d -> [ "-I"; d ]) (includes_of p t)
+  in
+  Array.of_list (((driver :: flags) @ [ "-MMD"; "-MF"; obj ^ ".d" ]) @ [ "-c"; src; "-o"; obj ])
+
+let link_libs p (t : target) =
+  let deps = List.rev (deps_of p t) in
+  (if deps = [] then [] else [ "-L"; p.tc.builddir ])
+  @ List.map (fun (d : target) -> "-l" ^ d.name) deps
+  @ List.concat_map (fun (d : target) -> d.ldflags) deps
+
+let has_cxx p (t : target) =
+  List.exists (fun s -> lang_of s = Cxx) (all_srcs t)
+  || List.exists (fun (d : target) -> List.exists (fun s -> lang_of s = Cxx) (all_srcs d)) (deps_of p t)
+
+let link_cmd p (t : target) objs =
+  let driver = if has_cxx p t then p.tc.cxx else p.tc.cc in
+  let out = out_of p t in
+  match t.kind with
+  | Lib -> Array.of_list ((p.tc.ar :: [ "rcs"; out ]) @ objs)
+  | Shared ->
+      let soname =
+        match t.soname with
+        | None -> []
+        | Some s ->
+            if p.platform = "darwin" then [ "-Wl,-install_name," ^ s ] else [ "-Wl,-soname," ^ s ]
+      in
+      Array.of_list
+        (((driver :: [ "-shared" ]) @ objs @ [ "-o"; out ]) @ soname @ link_libs p t @ t.ldflags
+       @ p.tc.ldflags)
+  | Bin | Test ->
+      Array.of_list (((driver :: objs) @ [ "-o"; out ]) @ link_libs p t @ t.ldflags @ p.tc.ldflags)
+
+let tag_of = function
+  | Lib -> ("ar", Style.magenta)
+  | Shared -> ("so", Style.cyan)
+  | Bin -> ("ld", Style.green)
+  | Test -> ("ld", Style.green)
+
+let is_header f =
+  List.mem (String.lowercase_ascii (Filename.extension f)) [ ".h"; ".hh"; ".hpp"; ".hxx"; ".inc" ]
+
+type t = { g : Graph.t; outputs : (string, int) Hashtbl.t; p : project }
+
+let of_project p =
+  let pic = pic_set p in
+  let nodes = ref [] in
+  let n = ref 0 in
+  let add spec = nodes := spec :: !nodes; incr n in
+  let gen_headers = List.concat_map (fun r -> List.filter is_header r.routs) p.rules in
+  List.iter
+    (fun r ->
+      let cmd = Array.of_list r.rcmd in
+      add
+        (Graph.make ~id:!n ~tag:"gen" ~label:r.rdesc ~cmd ~outs:r.routs ~ins:r.rin ()))
+    p.rules;
+  let outputs = Hashtbl.create 16 in
+  List.iter
+    (fun (t : target) ->
+      let objs =
+        List.map
+          (fun src ->
+            let obj = obj_of p t src in
+            let cmd = compile_cmd p ~pic t src obj in
+            let tag = if lang_of src = Cxx then "c++" else "cc" in
+            add
+              (Graph.make ~id:!n ~tag ~label:src ~cmd ~outs:[ obj ] ~ins:[ src ]
+                 ~depfile:(obj ^ ".d") ~ords:gen_headers ());
+            obj)
+          (all_srcs t)
+      in
+      let out = out_of p t in
+      let tag, _ = tag_of t.kind in
+      let ins = objs @ List.map (fun (d : target) -> out_of p d) (deps_of p t) in
+      let label = match t.kind with Lib | Shared -> Filename.basename out | _ -> t.name in
+      add (Graph.make ~id:!n ~tag ~label ~cmd:(link_cmd p t objs) ~outs:[ out ] ~ins ());
+      Hashtbl.replace outputs t.name (!n - 1))
+    p.targets;
+  { g = Graph.build (List.rev !nodes); outputs; p }
+
+let select b targets =
+  let roots = List.filter_map (fun (t : target) -> Hashtbl.find_opt b.outputs t.name) targets in
+  Graph.reachable b.g roots
+
+let paint tag text =
+  match tag with
+  | "cc" -> Style.blue text
+  | "c++" -> Style.blue text
+  | "ar" -> Style.magenta text
+  | "so" -> Style.cyan text
+  | "ld" -> Style.green text
+  | "gen" -> Style.yellow text
+  | _ -> text