ProgramMemory refactor - eliminate copies of memory (#5273)

* refactor program memory for encapsulation and remove special treatment of return values

Signed-off-by: Nick Cameron <nrc@ncameron.org>

* Refactor ProgramMemory to isolate mutation

Signed-off-by: Nick Cameron <nrc@ncameron.org>

* Refactor ProgramMemory

Signed-off-by: Nick Cameron <nrc@ncameron.org>

* Generated output

Signed-off-by: Nick Cameron <nrc@ncameron.org>

* Cache the result of executing modules for their items

Signed-off-by: Nick Cameron <nrc@ncameron.org>

* Compress envs when popped

Signed-off-by: Nick Cameron <nrc@ncameron.org>

* Remove the last traces of geometry from the memory module

Signed-off-by: Nick Cameron <nrc@ncameron.org>

* docs

Signed-off-by: Nick Cameron <nrc@ncameron.org>

* Fixups

Signed-off-by: Nick Cameron <nrc@ncameron.org>

* Frontend

Signed-off-by: Nick Cameron <nrc@ncameron.org>

* Improve Environment GC

Signed-off-by: Nick Cameron <nrc@ncameron.org>

* Fixup mock execution frontend and interpreter, misc bug fixes

Signed-off-by: Nick Cameron <nrc@ncameron.org>

---------

Signed-off-by: Nick Cameron <nrc@ncameron.org>

docs/kcl/types/EnvironmentRef.md

@@ -0,0 +1,16 @@
+---
+title: "EnvironmentRef"
+excerpt: ""
+layout: manual
+---
+
+
+[`SnapshotRef`](/docs/kcl/types/SnapshotRef)
+
+
+
+
+
+
+
+

docs/kcl/types/KclValue.md

@@ -311,7 +311,7 @@ Data for an imported geometry.
 | Property | Type | Description | Required |
 |----------|------|-------------|----------|
 | `type` |enum: `Function`|  | No |
-| `memory` |[`ProgramMemory`](/docs/kcl/types/ProgramMemory)| Any KCL value. | No |
+| `memory` |[`EnvironmentRef`](/docs/kcl/types/EnvironmentRef)| Any KCL value. | No |
 | `__meta` |`[` [`Metadata`](/docs/kcl/types/Metadata) `]`|  | No |
 
 
@@ -351,6 +351,23 @@ Data for an imported geometry.
 
 ----
 
+**Type:** `object`
+
+
+
+
+
+## Properties
+
+| Property | Type | Description | Required |
+|----------|------|-------------|----------|
+| `type` |enum: `Tombstone`|  | No |
+| `value` |`null`|  | No |
+| `__meta` |`[` [`Metadata`](/docs/kcl/types/Metadata) `]`|  | No |
+
+
+----
+
 
 
 

docs/kcl/types/ProgramMemory.md

@@ -17,6 +17,5 @@ layout: manual
 |----------|------|-------------|----------|
 | `environments` |`[` [`Environment`](/docs/kcl/types/Environment) `]`|  | No |
 | `currentEnv` |`integer`|  | No |
-| `return` |[`KclValue`](/docs/kcl/types/KclValue)|  | No |
 
 

docs/kcl/types/SnapshotRef.md

@@ -0,0 +1,16 @@
+---
+title: "SnapshotRef"
+excerpt: "An index pointing to a snapshot within a specific (unspecified) environment."
+layout: manual
+---
+
+An index pointing to a snapshot within a specific (unspecified) environment.
+
+**Type:** `integer` (`uint`)
+
+
+
+
+
+
+