// test: echo -e '(3 == 3) & (4 > 2)' | calc.exe | grep -q '=> 1'
// test: echo -e '3 == 3 & 4 > 2' | calc.exe | grep -q '=> 1'
// test: echo -e '1 + quit' | calc.exe | grep -q error
// test: echo -e '(3 == 3) & (4 > 2)' | calc.exe | grep -q '=> 1'
// test: echo -e '3 == 3 & 4 > 2' | calc.exe | grep -q '=> 1'
// test: echo -e '1 + quit' | calc.exe | grep -q error