empty predicate for lists defined
removing extraneous print statement
adding quit function that terminates program
standard library function 'or'
standard library function 'and'
standard library function 'xor'
standard library function '<=' and '>='
standard library function 'sum'
standard library function 'length'
standard library function 'append'
standard library function 'filter'
standard library function 'map'
ensure that cons second arg is a list
require cons's second arg to be list, but more better
add print and pp
add test for nested lambdas that I don't think helped
add 'do' which evals all args and returns last