3309

Rip out everything to fix one failing unit test (commit 3290; type
abbreviations).

This commit does several things at once that I couldn't come up with a
clean way to unpack:

  A. It moves to a new representation for type trees without changing
  the actual definition of the `type_tree` struct.

  B. It adds unit tests for our type metadata precomputation, so that
  errors there show up early and in a simpler setting rather than dying
  when we try to load Mu code.

  C. It fixes a bug, guarding against infinite loops when precomputing
  metadata for recursive shape-shifting containers. To do this it uses a
  dumb way of comparing type_trees, comparing their string
  representations instead. That is likely incredibly inefficient.

Perhaps due to C, this commit has made Mu incredibly slow. Running all
tests for the core and the edit/ app now takes 6.5 minutes rather than
3.5 minutes.

== more notes and details

I've been struggling for the past week now to back out of a bad design
decision, a premature optimization from the early days: storing atoms
directly in the 'value' slot of a cons cell rather than creating a
special 'atom' cons cell and storing it on the 'left' slot. In other
words, if a cons cell looks like this:

              o
            / | \
         left val right

..then the type_tree (a b c) used to look like this (before this
commit):

      o
      | \
      a   o
          | \
          b   o
              | \
              c   null

..rather than like this 'classic' approach to s-expressions which never
mixes val and right (which is what we now have):

      o
    /   \
   o      o
   |    /   \
   a   o      o
       |    /   \
       b   o      null
           |
           c

The old approach made several operations more complicated, most recently
the act of replacing a (possibly atom/leaf) sub-tree with another. That
was the final straw that got me to realize the contortions I was going
through to save a few type_tree nodes (cons cells).

Switching to the new approach was hard partly because I've been using
the old approach for so long and type_tree manipulations had pervaded
everything. Another issue I ran into was the realization that my layers
were not cleanly separated. Key parts of early layers (precomputing type
metadata) existed purely for far later ones (shape-shifting types).

Layers I got repeatedly stuck at:

  1. the transform for precomputing type sizes (layer 30)
  2. type-checks on merge instructions (layer 31)
  3. the transform for precomputing address offsets in types (layer 36)
  4. replace operations in supporting shape-shifting recipes (layer 55)

After much thrashing I finally noticed that it wasn't the entirety of
these layers that was giving me trouble, but just the type metadata
precomputation, which had bugs that weren't manifesting until 30 layers
later. Or, worse, when loading .mu files before any tests had had a
chance to run. A common failure mode was running into types at run time
that I hadn't precomputed metadata for at transform time.

Digging into these bugs got me to realize that what I had before wasn't
really very good, but a half-assed heuristic approach that did a whole
lot of extra work precomputing metadata for utterly meaningless types
like `((address number) 3)` which just happened to be part of a larger
type like `(array (address number) 3)`.

So, I redid it all. I switched the representation of types (because the
old representation made unit tests difficult to retrofit) and added unit
tests to the metadata precomputation. I also made layer 30 only do the
minimal metadata precomputation it needs for the concepts introduced
until then. In the process, I also made the precomputation more correct
than before, and added hooks in the right place so that I could augment
the logic when I introduced shape-shifting containers.

== lessons learned

There's several levels of hygiene when it comes to layers:

1. Every layer introduces precisely what it needs and in the simplest
way possible. If I was building an app until just that layer, nothing
would seem over-engineered.

2. Some layers are fore-shadowing features in future layers. Sometimes
this is ok. For example, layer 10 foreshadows containers and arrays and
so on without actually supporting them. That is a net win because it
lets me lay out the core of Mu's data structures out in one place. But
if the fore-shadowing gets too complex things get nasty. Not least
because it can be hard to write unit tests for features before you
provide the plumbing to visualize and manipulate them.

3. A layer is introducing features that are tested only in later layers.

4. A layer is introducing features with tests that are invalidated in
later layers. (This I knew from early on to be an obviously horrendous
idea.)

Summary: avoid Level 2 (foreshadowing layers) as much as possible.
Tolerate it indefinitely for small things where the code stays simple
over time, but become strict again when things start to get more
complex.

Level 3 is mostly a net lose, but sometimes it can be expedient (a real
case of the usually grossly over-applied term "technical debt"), and
it's better than the conventional baseline of no layers and no
scenarios. Just clean it up as soon as possible.

Definitely avoid layer 4 at any time.

== minor lessons

Avoid unit tests for trivial things, write scenarios in context as much as
possible. But within those margins unit tests are fine. Just introduce them
before any scenarios (commit 3297).

Reorganizing layers can be easy. Just merge layers for starters! Punt on
resplitting them in some new way until you've gotten them to work. This is the
wisdom of Refactoring: small steps.

What made it hard was not wanting to merge *everything* between layer 30
and 55. The eventual insight was realizing I just need to move those two
full-strength transforms and nothing else.

1 files changed, 234 insertions, 65 deletions

diff --git a/030container.cc b/030container.cc
index c24d6f7d..bb7ce08f 100644
--- a/030container.cc
+++ b/030container.cc
@@ -148,32 +148,41 @@ void clear_container_metadata() {
 if (r.metadata.size) return r.metadata.size;
 
 :(before "End size_of(type) Cases")
-if (type->value == -1) return 1;  // error value, but we'll raise it elsewhere
-if (type->value == 0) {
-  assert(!type->left && !type->right);
-  return 1;
+if (type->atom) {
+  if (type->value == -1) return 1;  // error value, but we'll raise it elsewhere
+  if (type->value == 0) return 1;
 }
-if (!contains_key(Type, type->value)) {
-  raise << "no such type " << type->value << '\n' << end();
+const type_tree* root = root_type(type);
+if (!contains_key(Type, root->value)) {
+  raise << "no such type " << root->value << '\n' << end();
   return 0;
 }
-type_info t = get(Type, type->value);
+type_info t = get(Type, root->value);
 if (t.kind == CONTAINER) {
   // Compute size_of Container
+  if (!contains_key(Container_metadata, type)) return 1;  // error raised elsewhere
   return get(Container_metadata, type).size;
 }
 
+:(code)
+const type_tree* root_type(const type_tree* t) {
+  const type_tree* result = t->atom ? t : t->left;
+  assert(result->atom);
+  return result;
+}
+
 //: precompute Container_metadata before we need size_of
 //: also store a copy in each reagent in each instruction in each recipe
-//: sometimes does unnecessary work for meaningless types
 
 :(after "Begin Instruction Modifying Transforms")  // needs to happen before transform_names, therefore after Type Modifying Transforms below
 Transform.push_back(compute_container_sizes);
 :(code)
 void compute_container_sizes(recipe_ordinal r) {
   recipe& caller = get(Recipe, r);
+  trace(9992, "transform") << "--- compute container sizes for " << caller.name << end();
   for (int i = 0; i < SIZE(caller.steps); ++i) {
     instruction& inst = caller.steps.at(i);
+    trace(9993, "transform") << "- compute container sizes for " << to_string(inst) << end();
     for (int i = 0; i < SIZE(inst.ingredients); ++i)
       compute_container_sizes(inst.ingredients.at(i));
     for (int i = 0; i < SIZE(inst.products); ++i)
@@ -185,37 +194,64 @@ void compute_container_sizes(reagent& r) {
   if (is_literal(r) || is_dummy(r)) return;
   reagent rcopy = r;
   // Compute Container Size(reagent rcopy)
-  set<type_ordinal> pending_metadata;
+  set<string> pending_metadata;
   compute_container_sizes(rcopy.type, pending_metadata);
   if (contains_key(Container_metadata, rcopy.type))
     r.metadata = get(Container_metadata, rcopy.type);
 }
 
-void compute_container_sizes(const type_tree* type, set<type_ordinal>& pending_metadata) {
+void compute_container_sizes(const type_tree* type, set<string>& pending_metadata) {
   if (!type) return;
-  if (contains_key(pending_metadata, type->value)) return;
-  if (type->value) pending_metadata.insert(type->value);
+  trace(9993, "transform") << "compute container sizes for " << to_string(type) << end();
   if (contains_key(Container_metadata, type)) return;
-  // might be needed by later layers, but we haven't found a need for it yet
-//?   if (type->left) compute_container_sizes(type->left, pending_metadata);
-  if (type->right) compute_container_sizes(type->right, pending_metadata);
+  if (contains_key(pending_metadata, names_to_string_without_quotes(type))) return;
+  pending_metadata.insert(names_to_string_without_quotes(type));
+//?   cerr << to_string(type) << '\n';
+  if (!type->atom) {
+    assert(type->left->atom);
+    if (type->left->name == "address") {
+//?       cerr << "  address\n";
+      compute_container_sizes(type->right, pending_metadata);
+    }
+    else if (type->left->name == "array") {
+      const type_tree* element_type = type->right;
+      // hack: support both array:number:3 and array:address:number
+//?       cerr << "  array\n";
+//?       cerr << "    " << to_string(type) << '\n';
+//?       cerr << "    " << to_string(element_type) << ' ' << element_type->atom << ' ' << element_type->right;
+//?       if (element_type->right)
+//?         cerr << " -- " << to_string(element_type->right) << ' ' << element_type->right->atom << ' ' << is_integer(element_type->right->name);
+//?       cerr << '\n';
+      if (!element_type->atom && element_type->right && element_type->right->atom && is_integer(element_type->right->name))
+        element_type = element_type->left;
+      compute_container_sizes(element_type, pending_metadata);
+    }
+    // End compute_container_sizes Non-atom Cases
+    return;
+  }
+  assert(type->atom);
   if (!contains_key(Type, type->value)) return;  // error raised elsewhere
   type_info& info = get(Type, type->value);
   if (info.kind == CONTAINER) {
-    // size of a container is the sum of the sizes of its element
-    // (So it can only contain arrays if they're static and include their
-    // length in the type.)
-    container_metadata metadata;
-    for (int i = 0; i < SIZE(info.elements); ++i) {
-      reagent/*copy*/ element = info.elements.at(i);
-      // Compute Container Size(element)
-      compute_container_sizes(element.type, pending_metadata);
-      metadata.offset.push_back(metadata.size);  // save previous size as offset
-      metadata.size += size_of(element.type);
-    }
-    Container_metadata.push_back(pair<type_tree*, container_metadata>(new type_tree(*type), metadata));
+    compute_container_sizes(info, type, pending_metadata);
+  }
+  // End compute_container_sizes Atom Cases
+}
+
+void compute_container_sizes(const type_info& container_info, const type_tree* full_type, set<string>& pending_metadata) {
+  assert(container_info.kind == CONTAINER);
+  // size of a container is the sum of the sizes of its element
+  // (So it can only contain arrays if they're static and include their
+  // length in the type.)
+  container_metadata metadata;
+  for (int i = 0; i < SIZE(container_info.elements); ++i) {
+    reagent/*copy*/ element = container_info.elements.at(i);
+    // Compute Container Size(element, full_type)
+    compute_container_sizes(element.type, pending_metadata);
+    metadata.offset.push_back(metadata.size);  // save previous size as offset
+    metadata.size += size_of(element.type);
   }
-  // End compute_container_sizes Cases
+  Container_metadata.push_back(pair<type_tree*, container_metadata>(new type_tree(*full_type), metadata));
 }
 
 container_metadata& get(vector<pair<type_tree*, container_metadata> >& all, const type_tree* key) {
@@ -239,7 +275,8 @@ bool contains_key(const vector<pair<type_tree*, container_metadata> >& all, cons
 bool matches(const type_tree* a, const type_tree* b) {
   if (a == b) return true;
   if (!a || !b) return false;
-  if (a->value != b->value) return false;
+  if (a->atom != b->atom) return false;
+  if (a->atom) return a->value == b->value;
   return matches(a->left, b->left) && matches(a->right, b->right);
 }
 
@@ -252,7 +289,122 @@ def main [
 ]
 +app: foo: 34 35 36
 
+//: for the following unit tests we'll do the work of the transform by hand
+
+:(before "End Unit Tests")
+void test_container_sizes() {
+  // a container we don't have the size for
+  reagent r("x:point");
+  CHECK(!contains_key(Container_metadata, r.type));
+  // scan
+  compute_container_sizes(r);
+  // the reagent we scanned knows its size
+  CHECK_EQ(r.metadata.size, 2);
+  // the global table also knows its size
+  CHECK(contains_key(Container_metadata, r.type));
+  CHECK_EQ(get(Container_metadata, r.type).size, 2);
+}
+
+void test_container_sizes_nested() {
+  // a container we don't have the size for
+  reagent r("x:point-number");
+  CHECK(!contains_key(Container_metadata, r.type));
+  // scan
+  compute_container_sizes(r);
+  // the reagent we scanned knows its size
+  CHECK_EQ(r.metadata.size, 3);
+  // the global table also knows its size
+  CHECK(contains_key(Container_metadata, r.type));
+  CHECK_EQ(get(Container_metadata, r.type).size, 3);
+}
+
+void test_container_sizes_recursive() {
+  // define a container containing an address to itself
+  run("container foo [\n"
+      "  x:number\n"
+      "  y:address:foo\n"
+      "]\n");
+  reagent r("x:foo");
+  compute_container_sizes(r);
+  CHECK_EQ(r.metadata.size, 2);
+}
+
+void test_container_sizes_from_address() {
+  // a container we don't have the size for
+  reagent container("x:point");
+  CHECK(!contains_key(Container_metadata, container.type));
+  // scanning an address to the container precomputes the size of the container
+  reagent r("x:address:point");
+  compute_container_sizes(r);
+  CHECK(contains_key(Container_metadata, container.type));
+  CHECK_EQ(get(Container_metadata, container.type).size, 2);
+}
+
+void test_container_sizes_from_array() {
+  // a container we don't have the size for
+  reagent container("x:point");
+  CHECK(!contains_key(Container_metadata, container.type));
+  // scanning an array of the container precomputes the size of the container
+  reagent r("x:array:point");
+  compute_container_sizes(r);
+  CHECK(contains_key(Container_metadata, container.type));
+  CHECK_EQ(get(Container_metadata, container.type).size, 2);
+}
+
+void test_container_sizes_from_address_to_array() {
+  // a container we don't have the size for
+  reagent container("x:point");
+  CHECK(!contains_key(Container_metadata, container.type));
+  // scanning an address to an array of the container precomputes the size of the container
+  reagent r("x:address:array:point");
+  compute_container_sizes(r);
+  CHECK(contains_key(Container_metadata, container.type));
+  CHECK_EQ(get(Container_metadata, container.type).size, 2);
+}
+
+void test_container_sizes_from_static_array() {
+  // a container we don't have the size for
+  reagent container("x:point");
+  int old_size = SIZE(Container_metadata);
+  // scanning an address to an array of the container precomputes the size of the container
+  reagent r("x:array:point:10");
+  compute_container_sizes(r);
+  CHECK(contains_key(Container_metadata, container.type));
+  CHECK_EQ(get(Container_metadata, container.type).size, 2);
+  // no non-container types precomputed
+  CHECK_EQ(SIZE(Container_metadata)-old_size, 1);
+}
+
+void test_container_sizes_from_address_to_static_array() {
+  // a container we don't have the size for
+  reagent container("x:point");
+  int old_size = SIZE(Container_metadata);
+  // scanning an address to an array of the container precomputes the size of the container
+  reagent r("x:address:array:point:10");
+  compute_container_sizes(r);
+  CHECK(contains_key(Container_metadata, container.type));
+  CHECK_EQ(get(Container_metadata, container.type).size, 2);
+  // no non-container types precomputed
+  CHECK_EQ(SIZE(Container_metadata)-old_size, 1);
+}
+
+void test_container_sizes_from_repeated_address_and_array_types() {
+  // a container we don't have the size for
+  reagent container("x:point");
+  int old_size = SIZE(Container_metadata);
+  // scanning repeated address and array types modifying the container precomputes the size of the container
+  reagent r("x:address:array:address:array:point:10");
+  compute_container_sizes(r);
+  CHECK(contains_key(Container_metadata, container.type));
+  CHECK_EQ(get(Container_metadata, container.type).size, 2);
+  // no non-container types precomputed
+  CHECK_EQ(SIZE(Container_metadata)-old_size, 1);
+}
+
 //:: To access elements of a container, use 'get'
+//: 'get' takes a 'base' container and an 'offset' into it and returns the
+//: appropriate element of the container value.
+
 :(scenario get)
 def main [
   12:number <- copy 34
@@ -273,11 +425,15 @@ case GET: {
   }
   reagent/*copy*/ base = inst.ingredients.at(0);  // new copy for every invocation
   // Update GET base in Check
-  if (!base.type || !base.type->value || !contains_key(Type, base.type->value) || get(Type, base.type->value).kind != CONTAINER) {
+  if (!base.type) {
+    raise << maybe(get(Recipe, r).name) << "first ingredient of 'get' should be a container, but got '" << inst.ingredients.at(0).original_string << "'\n" << end();
+    break;
+  }
+  const type_tree* base_root_type = base.type->atom ? base.type : base.type->left;
+  if (!base_root_type->atom || base_root_type->value == 0 || !contains_key(Type, base_root_type->value) || get(Type, base_root_type->value).kind != CONTAINER) {
     raise << maybe(get(Recipe, r).name) << "first ingredient of 'get' should be a container, but got '" << inst.ingredients.at(0).original_string << "'\n" << end();
     break;
   }
-  type_ordinal base_type = base.type->value;
   const reagent& offset = inst.ingredients.at(1);
   if (!is_literal(offset) || !is_mu_scalar(offset)) {
     raise << maybe(get(Recipe, r).name) << "second ingredient of 'get' should have type 'offset', but got '" << inst.ingredients.at(1).original_string << "'\n" << end();
@@ -288,14 +444,14 @@ case GET: {
     offset_value = to_integer(offset.name);
   else
     offset_value = offset.value;
-  if (offset_value < 0 || offset_value >= SIZE(get(Type, base_type).elements)) {
-    raise << maybe(get(Recipe, r).name) << "invalid offset '" << offset_value << "' for '" << get(Type, base_type).name << "'\n" << end();
+  if (offset_value < 0 || offset_value >= SIZE(get(Type, base_root_type->value).elements)) {
+    raise << maybe(get(Recipe, r).name) << "invalid offset '" << offset_value << "' for '" << get(Type, base_root_type->value).name << "'\n" << end();
     break;
   }
   if (inst.products.empty()) break;
   reagent/*copy*/ product = inst.products.at(0);
   // Update GET product in Check
-  const reagent/*copy*/ element = element_type(base.type, offset_value);
+  const reagent/*copy*/ element = element_type(base.type, offset_value);  // not just base_root_type because later layers will introduce compound types
   if (!types_coercible(product, element)) {
     raise << maybe(get(Recipe, r).name) << "'get " << base.original_string << ", " << offset.original_string << "' should write to " << names_to_string_without_quotes(element.type) << " but '" << product.name << "' has type " << names_to_string_without_quotes(product.type) << '\n' << end();
     break;
@@ -311,13 +467,13 @@ case GET: {
     raise << maybe(current_recipe_name()) << "tried to access location 0 in '" << to_original_string(current_instruction()) << "'\n" << end();
     break;
   }
-  type_ordinal base_type = base.type->value;
+  const type_tree* base_root_type = root_type(base.type);
   int offset = ingredients.at(1).at(0);
-  if (offset < 0 || offset >= SIZE(get(Type, base_type).elements)) break;  // copied from Check above
+  if (offset < 0 || offset >= SIZE(get(Type, base_root_type->value).elements)) break;  // copied from Check above
   assert(base.metadata.size);
   int src = base_address + base.metadata.offset.at(offset);
   trace(9998, "run") << "address to copy is " << src << end();
-  reagent/*copy*/ element = element_type(base.type, offset);
+  reagent/*copy*/ element = element_type(base.type, offset);  // not just base_root_type because later layers will introduce compound types
   element.set_value(src);
   trace(9998, "run") << "its type is " << names_to_string(element.type) << end();
   // Read element
@@ -328,9 +484,10 @@ case GET: {
 :(code)
 const reagent element_type(const type_tree* type, int offset_value) {
   assert(offset_value >= 0);
-  assert(contains_key(Type, type->value));
-  assert(!get(Type, type->value).name.empty());
-  const type_info& info = get(Type, type->value);
+  const type_tree* root = root_type(type);
+  assert(contains_key(Type, root->value));
+  assert(!get(Type, root->value).name.empty());
+  const type_info& info = get(Type, root->value);
   assert(info.kind == CONTAINER);
   if (offset_value >= SIZE(info.elements)) return reagent();  // error handled elsewhere
   reagent/*copy*/ element = info.elements.at(offset_value);
@@ -411,11 +568,15 @@ case PUT: {
   }
   reagent/*copy*/ base = inst.ingredients.at(0);
   // Update PUT base in Check
-  if (!base.type || !base.type->value || !contains_key(Type, base.type->value) || get(Type, base.type->value).kind != CONTAINER) {
+  if (!base.type) {
+    raise << maybe(get(Recipe, r).name) << "first ingredient of 'put' should be a container, but got '" << inst.ingredients.at(0).original_string << "'\n" << end();
+    break;
+  }
+  const type_tree* base_root_type = base.type->atom ? base.type : base.type->left;
+  if (!base_root_type->atom || base_root_type->value == 0 || !contains_key(Type, base_root_type->value) || get(Type, base_root_type->value).kind != CONTAINER) {
     raise << maybe(get(Recipe, r).name) << "first ingredient of 'put' should be a container, but got '" << inst.ingredients.at(0).original_string << "'\n" << end();
     break;
   }
-  type_ordinal base_type = base.type->value;
   reagent/*copy*/ offset = inst.ingredients.at(1);
   // Update PUT offset in Check
   if (!is_literal(offset) || !is_mu_scalar(offset)) {
@@ -425,8 +586,8 @@ case PUT: {
   int offset_value = 0;
   if (is_integer(offset.name)) {  // later layers permit non-integer offsets
     offset_value = to_integer(offset.name);
-    if (offset_value < 0 || offset_value >= SIZE(get(Type, base_type).elements)) {
-      raise << maybe(get(Recipe, r).name) << "invalid offset '" << offset_value << "' for '" << get(Type, base_type).name << "'\n" << end();
+    if (offset_value < 0 || offset_value >= SIZE(get(Type, base_root_type->value).elements)) {
+      raise << maybe(get(Recipe, r).name) << "invalid offset '" << offset_value << "' for '" << get(Type, base_root_type->value).name << "'\n" << end();
       break;
     }
   }
@@ -434,7 +595,7 @@ case PUT: {
     offset_value = offset.value;
   }
   const reagent& value = inst.ingredients.at(2);
-  const reagent& element = element_type(base.type, offset_value);
+  const reagent& element = element_type(base.type, offset_value);  // not just base_root_type because later layers will introduce compound types
   if (!types_coercible(element, value)) {
     raise << maybe(get(Recipe, r).name) << "'put " << base.original_string << ", " << offset.original_string << "' should write to " << names_to_string_without_quotes(element.type) << " but '" << value.name << "' has type " << names_to_string_without_quotes(value.type) << '\n' << end();
     break;
@@ -456,9 +617,9 @@ case PUT: {
     raise << maybe(current_recipe_name()) << "tried to access location 0 in '" << to_original_string(current_instruction()) << "'\n" << end();
     break;
   }
-  type_ordinal base_type = base.type->value;
+  const type_tree* base_root_type = root_type(base.type);
   int offset = ingredients.at(1).at(0);
-  if (offset < 0 || offset >= SIZE(get(Type, base_type).elements)) break;  // copied from Check above
+  if (offset < 0 || offset >= SIZE(get(Type, base_root_type->value).elements)) break;  // copied from Check above
   int address = base_address + base.metadata.offset.at(offset);
   trace(9998, "run") << "address to copy to is " << address << end();
   // optimization: directly write the element rather than updating 'product'
@@ -592,21 +753,23 @@ void insert_container(const string& command, kind_of_type kind, istream& in) {
 
 void replace_unknown_types_with_unique_ordinals(type_tree* type, const type_info& info) {
   if (!type) return;
-  if (!type->name.empty()) {
-    if (contains_key(Type_ordinal, type->name)) {
-      type->value = get(Type_ordinal, type->name);
-    }
-    else if (is_integer(type->name)) {  // sometimes types will contain non-type tags, like numbers for the size of an array
-      type->value = 0;
-    }
-    // End insert_container Special-cases
-    else if (type->name != "->") {  // used in recipe types
-      put(Type_ordinal, type->name, Next_type_ordinal++);
-      type->value = get(Type_ordinal, type->name);
-    }
+  if (!type->atom) {
+    replace_unknown_types_with_unique_ordinals(type->left, info);
+    replace_unknown_types_with_unique_ordinals(type->right, info);
+    return;
+  }
+  assert(!type->name.empty());
+  if (contains_key(Type_ordinal, type->name)) {
+    type->value = get(Type_ordinal, type->name);
+  }
+  else if (is_integer(type->name)) {  // sometimes types will contain non-type tags, like numbers for the size of an array
+    type->value = 0;
+  }
+  // End insert_container Special-cases
+  else if (type->name != "->") {  // used in recipe types
+    put(Type_ordinal, type->name, Next_type_ordinal++);
+    type->value = get(Type_ordinal, type->name);
   }
-  replace_unknown_types_with_unique_ordinals(type->left, info);
-  replace_unknown_types_with_unique_ordinals(type->right, info);
 }
 
 void skip_bracket(istream& in, string message) {
@@ -687,6 +850,11 @@ void check_or_set_invalid_types(const recipe_ordinal r) {
 void check_or_set_invalid_types(type_tree* type, const string& block, const string& name) {
   if (!type) return;  // will throw a more precise error elsewhere
   // End Container Type Checks
+  if (!type->atom) {
+    check_or_set_invalid_types(type->left, block, name);
+    check_or_set_invalid_types(type->right, block, name);
+    return;
+  }
   if (type->value == 0) return;
   if (!contains_key(Type, type->value)) {
     assert(!type->name.empty());
@@ -695,8 +863,6 @@ void check_or_set_invalid_types(type_tree* type, const string& block, const stri
     else
       raise << block << "unknown type " << type->name << " in " << name << '\n' << end();
   }
-  check_or_set_invalid_types(type->left, block, name);
-  check_or_set_invalid_types(type->right, block, name);
 }
 
 :(scenario container_unknown_field)
@@ -738,10 +904,13 @@ void check_container_field_types() {
 
 void check_invalid_types(const type_tree* type, const string& block, const string& name) {
   if (!type) return;  // will throw a more precise error elsewhere
+  if (!type->atom) {
+    check_invalid_types(type->left, block, name);
+    check_invalid_types(type->right, block, name);
+    return;
+  }
   if (type->value != 0) {  // value 0 = compound types (layer parse_tree) or type ingredients (layer shape_shifting_container)
     if (!contains_key(Type, type->value))
       raise << block << "unknown type in " << name << '\n' << end();
   }
-  check_invalid_types(type->left, block, name);
-  check_invalid_types(type->right, block, name);
 }