className: identifier
subroutineName: identifier

class: 'class' className '{'
  classVarDec*
  subroutineDec*
  '}'

classVarDec:
  ('static' | 'field')
  type
  varName (',' varName)* ';'

subroutineDec:
  ('constructor' | 'function' | 'method')
  ('void' | type)
  subroutineName
  '(' parameterList ')' subroutineBody

parameterList: don't worry about this yet

subroutineBody: '{' varDec* statements '}'

varDec: 'var' type varName (',' varName)* ';'

statements: statement*

statement:
  letStatement | ifStatement | whileStatement
  | doStatement | returnStatement

doStatement: 'do' subroutineCall ';'

expression: term (op term)*

term: integerConstant
  | stringConstant
  | keywordConstant
  | '(' expression ')'
  | unaryOp term

  | varName
  | varName '[' expression ']'
  | subroutineCall

subroutineCall: subroutineName '(' expressionList ')'
  | (className | varName) '.' subroutineName '(' ... ')'

Main.main(blah)   -- calling a 'function'
f.foo(bar)        -- calling the 'method' foo on the object f
foo(bar)          -- calling function/method within
                  -- current class

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