use ast nodes everywhere
build
evaluator test is nodes test
node tests by node type
begin visitor pattern for evaluator
initial evaluator tests
evaluate reference test
visitor pattern for comparisons
tests for unbound variable visitor
visit literal is common
abstract visitor class
abstract comparator conversion
prefactor infix visitors
visitor pattern for addition
delete extraneous constructors
visitor pattern for subtraction
visitor pattern for multiplication and division evaluation
visitor pattern for concat, and, and or
delete vestigial code
visitor pattern for function calls