prog8/README.md

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Prog8 - Structured Programming Language for 8-bit 6502/65c02 microprocessors
============================================================================

*Written by Irmen de Jong (irmen@razorvine.net)*

*Software license: GNU GPL 3.0, see file LICENSE*


This is a structured programming language for the 8-bit 6502/6510/65c02 microprocessor from the late 1970's and 1980's
as used in many home computers from that era. It is a medium to low level programming language,
which aims to provide many conveniences over raw assembly code (even when using a macro assembler).

Documentation
-------------
Full documentation (syntax reference, how to use the language and the compiler, etc.) can be found at:
https://prog8.readthedocs.io/


What does Prog8 provide?
------------------------

- big reduction of source code length over raw assembly
- modularity, symbol scoping, subroutines
- various data types other than just bytes (16-bit words, floats, strings)
- automatic variable allocations, automatic string and array variables and string sharing
- subroutines with an input- and output parameter signature
- no stack frame allocations because parameters and local variables are automatically allocated statically
- constant folding in expressions and other high-level program optimizations
- conditional branches
- floating point operations  (requires the C64 Basic ROM routines for this)
- 'when' statement to provide a concise jump table alternative to if/elseif chains
- many built-in functions such as ``sin``, ``cos``, ``rnd``, ``abs``, ``min``, ``max``, ``sqrt``, ``msb``, ``rol``, ``ror``, ``swap``, ``memset``, ``memcopy``, ``sort`` and ``reverse``
- structs to group together sets of variables and manipulate them at once
- convenience abstractions for low level aspects such as ZeroPage handling, program startup, explicit memory addresses
- fast execution speed due to compilation to native assembly code
- inline assembly allows you to have full control when every cycle or byte matters

*Rapid edit-compile-run-debug cycle:*

- use a modern PC to do the work on, use nice editors and enjoy quick compilation times
- can automatically run the program in the Vice emulator after succesful compilation
- breakpoints, that let the Vice emulator drop into the monitor if execution hits them
- source code labels automatically loaded in Vice emulator so it can show them in disassembly

*Two supported compiler targets* (contributions to improve these or to add support for other machines are welcome!):

- "c64": Commodore-64  (6510 CPU = almost a 6502), the main target.
- "cx16": [CommanderX16](https://www.commanderx16.com)  (65c02 CPU) .
- If you only use standard kernel and prog8 library routines, it is possible to compile the *exact same program* for both machines (just change the compiler target flag)!



Additional required tools
-------------------------

[64tass](https://sourceforge.net/projects/tass64/) - cross assembler. Install this on your shell path.
A recent .exe version of this tool for Windows can be obtained from my [clone](https://github.com/irmen/64tass/releases) of this project.
For other platforms it is very easy to compile it yourself (make ; make install).

A **Java runtime (jre or jdk), version 11 or newer**  is required to run a prepackaged version of the compiler.
If you want to build it from source, you'll need a Java SDK + Kotlin 1.3.x SDK (or for instance,
IntelliJ IDEA with the Kotlin plugin).

It's handy to have an emulator (or a real machine perhaps!) to run the programs on. The compiler assumes the presence
of the [Vice emulator](http://vice-emu.sourceforge.net/)  for the C64 target,
and the [x16emu emulator](https://github.com/commanderx16/x16-emulator) for the CommanderX16 target.


Example code
------------

This code calculates prime numbers using the Sieve of Eratosthenes algorithm::

    %import textio
    %zeropage basicsafe
    
    main {
    
        ubyte[256] sieve
        ubyte candidate_prime = 2       ; is increased in the loop
    
        sub start() {
            ; clear the sieve, to reset starting situation on subsequent runs
            memset(sieve, 256, false)   
            ; calculate primes
            txt.print("prime numbers up to 255:\n\n")
            ubyte amount=0
            repeat {
                ubyte prime = find_next_prime()
                if prime==0
                    break
                txt.print_ub(prime)
                txt.print(", ")
                amount++
            }
            txt.chrout('\n')
            txt.print("number of primes (expected 54): ")
            txt.print_ub(amount)
            txt.chrout('\n')
        }
    
        sub find_next_prime() -> ubyte {
            while sieve[candidate_prime] {
                candidate_prime++
                if candidate_prime==0
                    return 0        ; we wrapped; no more primes available in the sieve
            }
    
            ; found next one, mark the multiples and return it.
            sieve[candidate_prime] = true
            uword multiple = candidate_prime
    
            while multiple < len(sieve) {
                sieve[lsb(multiple)] = true
                multiple += candidate_prime
            }
            return candidate_prime
        }
    }



when compiled an ran on a C-64 you'll get:

![c64 screen](docs/source/_static/primes_example.png)

One of the included examples (wizzine.p8) animates a bunch of sprite balloons and looks like this:

![wizzine screen](docs/source/_static/wizzine.png)

Another example (cube3d-sprites.p8) draws the vertices of a rotating 3d cube:

![cube3d screen](docs/source/_static/cube3d.png)

If you want to play a video game, a fully working Tetris clone is included in the examples:

![tehtriz_screen](docs/source/_static/tehtriz.png)

The CommanderX16 compiler target is quite capable already too, here's a well known space ship 
animated in 3D with hidden line removal, in the CommanderX16 emulator:

![cobra3d](docs/source/_static/cobra3d.png)