[suzuki]

In my experiment, the Crystal version (https://github.com/nukata/little-scheme-in-crystal) was 38x faster than the Ruby version (https://github.com/nukata/little-scheme-in-ruby) and comparable to the Java version (https://github.com/nukata/little-scheme-in-java). Indeed, it is in the fastest group. See https://github.com/nukata/little-scheme#performance