Elements of Computing Systems Chapter 11b

## Exercises

We began the meeting by picking off where we were last time: completing the SymbolTable implementation and using it to decorate our XML output with the context necessary for eventual VM code output.

We decided to use a test to drive out the missing start_subroutine method on our SymbolTable: eschewing the book's advice to use two hash tables and instead opting for some good, old-fashioned state mutation:

• Implement SymbolTable#start_subroutine;

With that complete, we could now go through the XML generating Parser and add attributes to each identifier with their type, kind and index:

• Add symbol table information to all XML identifier nodes.

This concluded our adventures with XML and we began the process of converting our XML output to VM code by implementing the book's suggested VMWriter API:

• Implement VMWriter.

We then began a new Compilation Engine, combining our existing Tokenizer and VMWriter to actually compile Jack programs into VM code:

• WIP Compilation Engine

## Aside

There were quite a few entertaining asides this meeting:

• Tom showed how Ruby's Enumerable#count can take an item as an argument for counting specific occurrences;

• Paul relished using Ruby's rather odd heredoc syntax in a method call:

some_function(<<XML, <<YML, <<EOF)
<root/>
XML
foo:
  bar
YML
A really long string
EOF

• Both Chris and Leo pointed out that & repeats the last substitution in Vim;

• They also pointed out that ; repeats the last motion using t or f.

Thanks

Thanks to Leo & Paul and Geckoboard for typing and hosting respectively.