Simply directly run the binary `bin/picrin` from terminal, or you can use `make` to execute it like this.
$ make run
In the default option, when `make` command is called without arguments, it builds the binary and right after that dropped into the picrin interactive shell (REPL).
The compilation is tested only on Mac OSX. I think (or hope) it'll be ok to compile and run on other operating systems such as Linux or Windows, but there's no guarantee :(