https://en.wikipedia.org/wiki/SKI_combinator_calculus
start REPL with cargo run
Enter a SKI expression (a string consisting of S,K,I)
to exit, enter quit
https://en.wikipedia.org/wiki/SKI_combinator_calculus
start REPL with cargo run
Enter a SKI expression (a string consisting of S,K,I)
to exit, enter quit