-# The mem array constitutes the memory of the VM. It has the following geography:
-#
-# mem = +-----------------------+
-# | Built-in Variables |
-# +-----------------------+
-# | Return Stack |
-# +-----------------------+
-# | Parameter Stack |
-# +-----------------------+
-# | Terminal Input Buffer |
-# +-----------------------+
-# | Dictionary |
-# +-----------------------+
-#
-# Note that all words (user-defined, primitive, variables, etc) are included in
-# the dictionary.
-#
-# Simple linear addressing is used with one exception: references to primitive code
-# blocks, which are represented as anonymous functions, appear as negative indicies
-# into the primitives array which contains these functions.
-