The previous section has developed a basic vocabulary for statements
such as “the virtual machine code for the identity function is
(nil,(nil,nil))”, which are elaborated extensively in the
subsequent sections on code and data formats. However, a description in
this style would be inadequate without an explanation of how such an
entity as (nil,(nil,nil)) is communicated to avram in a
virtual machine code file. The purpose of this section is to fill the
gap by explaining exactly how any given tree would be transformed to its
concrete representation.
The syntax is based on a conversion of the trees to bit strings,
followed by grouping the bits into blocks of six, which are then encoded
by printable characters. Although anyone is free to modify avram,
it is recommended that the concrete syntax described here be maintained
for the sake of portability of virtual machine code applications.
Building a tree by reading the data from a file requires a more
difficult algorithm than the one presented in this section, and is not
considered because it's not strictly necessary for a
compiler. Procedures for both reading and writing are available to C and
C++ users as part of the avram library, and are also easily
invoked on the virtual code level.