diff --git a/gleam.toml b/gleam.toml
index 0d10db8..203162a 100644
--- a/gleam.toml
+++ b/gleam.toml
@@ -24,3 +24,4 @@ glexer = ">= 1.0.1 and < 2.0.0"
 gleescript = ">= 1.4.0 and < 2.0.0"
 pprint = ">= 1.0.3 and < 2.0.0"
 gleeunit = ">= 1.2.0 and < 2.0.0"
+temporary = ">= 1.0.0 and < 2.0.0"
diff --git a/manifest.toml b/manifest.toml
index 9835223..8d94dbd 100644
--- a/manifest.toml
+++ b/manifest.toml
@@ -3,9 +3,12 @@
 
 packages = [
   { name = "argv", version = "1.0.2", build_tools = ["gleam"], requirements = [], otp_app = "argv", source = "hex", outer_checksum = "BA1FF0929525DEBA1CE67256E5ADF77A7CDDFE729E3E3F57A5BDCAA031DED09D" },
+  { name = "envoy", version = "1.0.1", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "envoy", source = "hex", outer_checksum = "CFAACCCFC47654F7E8B75E614746ED924C65BD08B1DE21101548AC314A8B6A41" },
+  { name = "exception", version = "2.0.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "exception", source = "hex", outer_checksum = "F5580D584F16A20B7FCDCABF9E9BE9A2C1F6AC4F9176FA6DD0B63E3B20D450AA" },
   { name = "filepath", version = "1.0.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "filepath", source = "hex", outer_checksum = "EFB6FF65C98B2A16378ABC3EE2B14124168C0CE5201553DE652E2644DCFDB594" },
   { name = "glam", version = "2.0.1", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "glam", source = "hex", outer_checksum = "66EC3BCD632E51EED029678F8DF419659C1E57B1A93D874C5131FE220DFAD2B2" },
   { name = "glance", version = "0.11.0", build_tools = ["gleam"], requirements = ["gleam_stdlib", "glexer"], otp_app = "glance", source = "hex", outer_checksum = "8F3314D27773B7C3B9FB58D8C02C634290422CE531988C0394FA0DF8676B964D" },
+  { name = "gleam_crypto", version = "1.3.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_crypto", source = "hex", outer_checksum = "ADD058DEDE8F0341F1ADE3AAC492A224F15700829D9A3A3F9ADF370F875C51B7" },
   { name = "gleam_erlang", version = "0.25.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_erlang", source = "hex", outer_checksum = "054D571A7092D2A9727B3E5D183B7507DAB0DA41556EC9133606F09C15497373" },
   { name = "gleam_stdlib", version = "0.39.0", build_tools = ["gleam"], requirements = [], otp_app = "gleam_stdlib", source = "hex", outer_checksum = "2D7DE885A6EA7F1D5015D1698920C9BAF7241102836CE0C3837A4F160128A9C4" },
   { name = "gleescript", version = "1.4.0", build_tools = ["gleam"], requirements = ["argv", "filepath", "gleam_erlang", "gleam_stdlib", "simplifile", "snag", "tom"], otp_app = "gleescript", source = "hex", outer_checksum = "8CDDD29F91064E69950A91A40061785F10275ADB70A0520075591F61A724C455" },
@@ -14,6 +17,7 @@ packages = [
   { name = "pprint", version = "1.0.3", build_tools = ["gleam"], requirements = ["glam", "gleam_stdlib"], otp_app = "pprint", source = "hex", outer_checksum = "76BBB92E23D12D954BD452686543F29EDE8EBEBB7FC0ACCBCA66EEF276EC3A06" },
   { name = "simplifile", version = "2.0.1", build_tools = ["gleam"], requirements = ["filepath", "gleam_stdlib"], otp_app = "simplifile", source = "hex", outer_checksum = "5FFEBD0CAB39BDD343C3E1CCA6438B2848847DC170BA2386DF9D7064F34DF000" },
   { name = "snag", version = "0.3.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "snag", source = "hex", outer_checksum = "54D32E16E33655346AA3E66CBA7E191DE0A8793D2C05284E3EFB90AD2CE92BCC" },
+  { name = "temporary", version = "1.0.0", build_tools = ["gleam"], requirements = ["envoy", "exception", "filepath", "gleam_crypto", "gleam_stdlib", "simplifile"], otp_app = "temporary", source = "hex", outer_checksum = "51C0FEF4D72CE7CA507BD188B21C1F00695B3D5B09D7DFE38240BFD3A8E1E9B3" },
   { name = "tom", version = "1.0.1", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "tom", source = "hex", outer_checksum = "9EECB60150E834A07238BD5C7DF1FF07F7D4C5862BB8A773923D1981C7875FB0" },
 ]
 
@@ -27,3 +31,4 @@ gleeunit = { version = ">= 1.2.0 and < 2.0.0" }
 glexer = { version = ">= 1.0.1 and < 2.0.0" }
 pprint = { version = ">= 1.0.3 and < 2.0.0" }
 simplifile = { version = ">= 2.0.1 and < 3.0.0" }
+temporary = { version = ">= 1.0.0 and < 2.0.0" }
diff --git a/src/macabre.gleam b/src/macabre.gleam
index 13dfc49..dcc4c20 100644
--- a/src/macabre.gleam
+++ b/src/macabre.gleam
@@ -28,7 +28,9 @@ pub fn usage(message: String) -> Nil {
   io.println("Usage: macabre <filename.gleam>\n\n" <> message)
 }
 
-fn write_program(program: program.CompiledProgram) -> Result(Nil, errors.Error) {
+pub fn write_program(
+  program: program.CompiledProgram,
+) -> Result(Nil, errors.Error) {
   let build_directory = program.build_directory(program.base_directory)
   let source_directory = program.source_directory(program.base_directory)
   output.delete(build_directory)
diff --git a/test/compiler/directory_structure_tests.gleam b/test/compiler/directory_structure_tests.gleam
new file mode 100644
index 0000000..79ad123
--- /dev/null
+++ b/test/compiler/directory_structure_tests.gleam
@@ -0,0 +1,146 @@
+import compiler
+import compiler/program
+import filepath
+import gleam/dict
+import gleam/list
+import gleam/option
+import gleam/set
+import gleam/string
+import gleeunit/should
+import macabre
+import simplifile
+import temporary
+
+// These tests have to touch the filesystem, so
+// they add measurably to the compile time.
+// Tests in other files are pure and require no IO.
+// This file should *only* test that stuff is being placed
+// in the right directories. 
+//
+// I tried to bulk all the situations in just one test, but
+// it may have to be split out if it becomes too hard to
+// maintain.
+
+pub type ProjectFiles {
+  ProjectFiles(
+    base_dir: String,
+    src_dir: String,
+    build_dir: String,
+    main_path: String,
+  )
+}
+
+fn init_folders(
+  use_function: fn(ProjectFiles) -> a,
+) -> Result(a, simplifile.FileError) {
+  use dir <- temporary.create(temporary.directory())
+  let project_name = filepath.base_name(dir)
+  let src = filepath.join(dir, "src")
+  let build = filepath.join(dir, "build")
+  let main_path = filepath.join(src, project_name <> ".gleam")
+
+  simplifile.create_directory_all(src)
+  |> should.be_ok
+  let project_files =
+    ProjectFiles(
+      base_dir: dir,
+      src_dir: src,
+      build_dir: build,
+      main_path: main_path,
+    )
+  use_function(project_files)
+}
+
+pub fn program_compile_test_with_nested_folders_test() {
+  // src/<dirname.gleam>
+  // src/baz.py
+  // src/foo/bar.gleam
+  // src/foo/bindings.py
+  use project_files <- init_folders()
+  simplifile.write(
+    to: project_files.main_path,
+    contents: "import foo/bar
+
+  @external(python, \"baz\", \"baz\")
+  fn baz() -> Nil
+
+
+  pub fn main() {}",
+  )
+  |> should.be_ok
+
+  simplifile.write(
+    to: filepath.join(project_files.src_dir, "baz.py"),
+    contents: "
+  fn baz():
+      print('baz')",
+  )
+  |> should.be_ok
+
+  let foo_dir = filepath.join(project_files.src_dir, "foo")
+  simplifile.create_directory_all(foo_dir)
+  |> should.be_ok
+  simplifile.write(
+    to: filepath.join(foo_dir, "bar.gleam"),
+    contents: "@external(python, \"foo.bindings\", \"bar\")
+  fn bar() -> Nil",
+  )
+  |> should.be_ok
+
+  simplifile.write(
+    to: filepath.join(foo_dir, "bindings.py"),
+    contents: "def bar():
+      pass",
+  )
+  |> should.be_ok
+
+  let gleam_program =
+    program.load_program(project_files.base_dir)
+    |> should.be_ok
+
+  // load
+
+  should.equal(gleam_program.base_directory, project_files.base_dir)
+  should.equal(
+    gleam_program.main_module,
+    filepath.base_name(project_files.main_path),
+  )
+  gleam_program.modules
+  |> dict.size
+  |> should.equal(2)
+  gleam_program.external_import_files |> set.size |> should.equal(2)
+
+  // ---  compile
+  let compiled_program = compiler.compile_program(gleam_program)
+  should.equal(compiled_program.base_directory, project_files.base_dir)
+  should.equal(
+    compiled_program.main_module,
+    option.Some(
+      filepath.base_name(project_files.main_path) |> string.drop_right(6),
+    ),
+  )
+  compiled_program.modules
+  |> dict.size
+  |> should.equal(2)
+  compiled_program.external_import_files |> set.size |> should.equal(2)
+
+  // --- write output
+  macabre.write_program(compiled_program) |> should.be_ok
+
+  simplifile.read_directory(project_files.build_dir)
+  |> should.be_ok
+  |> list.sort(string.compare)
+  |> should.equal([
+    filepath.base_name(project_files.main_path) |> string.drop_right(6) <> ".py",
+    "__main__.py",
+    "baz.py",
+    "foo",
+    "gleam_builtins.py",
+  ])
+
+  project_files.build_dir
+  |> filepath.join("foo")
+  |> simplifile.read_directory
+  |> should.be_ok
+  |> should.equal(["bindings.py", "bar.py"])
+}