# full

fn two = () => {
  return 2
}

==>

Program(FunctionDeclaration(fn,
                            VariableDefinition,
                            Equals,
                            ParamList,
                            Arrow,
                            Body(ReturnStatement(return,
                                                 Number))))

# = is optional

fn one () => {
  return 1
}

==>

Program(FunctionDeclaration(fn,
                            VariableDefinition,
                            ParamList,
                            Arrow,
                            Body(ReturnStatement(return,
                                                 Number))))

# => is optional

fn one = () {
  return 1
}

==>

Program(FunctionDeclaration(fn,
                            VariableDefinition,
                            Equals,
                            ParamList,
                            Body(ReturnStatement(return,
                                                 Number))))

# terse

fn two() {
  return 2
}

==>

Program(FunctionDeclaration(fn,
                            VariableDefinition,
                            ParamList,
                            Body(ReturnStatement(return,
                                                 Number))))