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A 6502-oriented low-level programming language supporting advanced static analysis
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README.md

SixtyPical

Version 0.17. Work-in-progress, everything is subject to change.

SixtyPical is a 6502-like programming language with advanced static analysis.

"6502-like" means that it has similar restrictions as programming in 6502 assembly (e.g. the programmer must choose the registers that values will be stored in) and is concomitantly easy for a compiler to translate it to 6502 machine language code.

"Advanced static analysis" includes abstract interpretation, where we go through the program step by step, tracking not just the changes that happen during a specific execution of the program, but sets of changes that could possibly happen in any run of the program. This lets us determine that certain things can never happen, which we can then formulate as safety checks.

In practice, this means it catches things like

  • you forgot to clear carry before adding something to the accumulator
  • a subroutine that you call trashes a register you thought was preserved
  • you tried to read or write a byte beyond the end of a byte array
  • you tried to write the address of something that was not a routine, to a jump vector

and suchlike. It also provides some convenient operations based on machine-language programming idioms, such as

  • copying values from one register to another (via a third register when there are no underlying instructions that directly support it); this includes 16-bit values, which are copied in two steps
  • explicit tail calls
  • indirect subroutine calls

The reference implementation can analyze and compile SixtyPical programs to 6502 machine code.

Quick Start

If you have the VICE emulator installed, from this directory, you can run

./loadngo.sh c64 eg/c64/hearts.60p

and it will compile the hearts.60p source code and automatically start it in the x64 emulator, and you should see:

Screenshot of result of running hearts.60p

You can try the loadngo.sh script on other sources in the eg directory tree, which contains more extensive examples, including an entire game(-like program); see eg/README.md for a listing.

Documentation