To run the program, build it first by running "sh build.sh"
it should make a program called pl0, you can do

./pl0 source-file to run a source file or

./pl0 -p instruction-file to run it as a instruction file

I made some sample inputs in input/ that you can run it on, if there is 
any bugs you find, let me know and I will try to fix them.

This pl0 has a fixed stack and fix code buffer, so any very long program
or something that uses too much stack will error. You can adjust accordingly
in dat.h, though the problem is of that compiler will get errors if you make
the global types too big. The right fix is to dynamic allocate memory for
these structures but this is a toy so who cares.