I have just updated my Scheme interpreter in Crystal (https://github.com/nukata/little-scheme-in-crystal), which I used on the above benchmark test, along to Crystal 0.34.

The release notes of Crystal 0.34 say "Having as much as possible portable code is part of the goal of the std-lib. One of the areas that were in need of polishing was how Errno and WinError were handled. The Errno and WinError exceptions are now gone, and were replaced by a new hierarchy of exceptions." So I have modified

    rescue ex: Errno
      raise ErrorException.new(ex.message, NONE) if ex.errno == Errno::EPIPE

to

    rescue ex: IO::Error
      raise ErrorException.new(ex.message, NONE) if ex.os_error == Errno::EPIPE

though it is still dependent on POSIX. >_<