Updated Roadmap (markdown)

Roadmap.md

@@ -1,24 +1,35 @@
 # Roadmap
 
+## Near-Term
 - Finish compiler implementation (parity with interpreter features)
   - Array pass by reference
   - Work out how to evaluate expressions with only constants within the compiler so array dimensions no longer need to be literal constants
+- Write a non-trivial app in EightBall to discover the pain points
+
+## Medium-Term
 - Wishlist features:
-  - Multidimensional arrays (implemented as array of pointers to array).
+  - Multidimensional arrays
+    - 2D array is implemented as array of pointers to arrays of `word` or `byte`.
+    - 3D array is implemented as array of pointers to array of pointers to arrays of `word` or `byte`.
+    - etc.
   - Array initializer lists:
     - `word xyz[3] = {123, 456, 789}`
   - String initializer:
     - `byte qq[10] = "abcde"` - will also add null terminator to string
+  - A way to pass string literals as subroutine arguments
   - Module system
     - Would be good to make bytecode relocatable by using relative addresses
     - Need to add new relative jump / branch instructions for this)
     - Drawback is it makes the code harder to read for humans, but this can be overcome with better tools
     - Need to think about how a module system should work
-- Write a non-trivial app in EightBall to discover the pain points
 - Optimize virtual machine bytecodes, based on study of real code
   - For example, it would be good to have an instruction to drop n bytes from call stack rather than repeated `POP`, `DROP` as the compiler currently does.
-- High performance VM: hand-coded in 6502 assembly
 
+## Long-Term
+- High performance VM
+  - Hand-coded in 6502 assembly
+
+# Ground Rules
 Features will only be added if:
 1. They do not increase the code size so much that it is no longer practical to run EightBall on Apple II and C64.  (VIC20+32K is already a tight fit.)
 2. Language features must have both an interpreter and compiler implementation.