Prog8 - Structured Programming Language for 8-bit 6502/6510 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 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):

• reduction of source code length
• easier program understanding (because it's higher level, and more terse)
• option to automatically run the compiled program in the Vice emulator
• modularity, symbol scoping, subroutines
• subroutines have enforced input- and output parameter definitions
• various data types other than just bytes (16-bit words, floats, strings, 16-bit register pairs)
• automatic variable allocations, automatic string variables and string sharing
• constant folding in expressions (compile-time evaluation)
• automatic type conversions
• floating point operations
• abstracting away low level aspects such as ZeroPage handling, program startup, explicit memory addresses
• 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
• conditional gotos
• various code optimizations (code structure, logical and numerical expressions, ...)

It is mainly targeted at the Commodore-64 machine at this time.

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 8 or newer is required to run the packaged compiler. If you want to build it from source, you'll need a Kotlin 1.3 SDK as well (or for instance, IntelliJ IDEA with the Kotlin plugin).

It's handy to have a C-64 emulator or a real C-64 to run the programs on. The compiler assumes the presence of the Vice emulator <http://vice-emu.sourceforge.net/>_.

Example code

When this code is compiled::

%import c64lib
%import c64utils
%import c64flt

~ main {
    sub start() {
        ; set text color and activate lowercase charset
        c64.COLOR = 13
        c64.VMCSB |= 2

        ; use optimized routine to write text
        c64scr.print("Hello!\n")

        ; use iteration to write text
        str question = "How are you?\n"
        for ubyte char in question
            c64.CHROUT(char)

        ; use indexed loop to write characters
        str bye = "Goodbye!\n"
        for ubyte c in 0 to len(bye)
            c64.CHROUT(bye[c])


        float clock_seconds = ((mkword(c64.TIME_LO, c64.TIME_MID) as float) + (c64.TIME_HI as float)*65536.0) / 60
        float hours = floor(clock_seconds / 3600)
        clock_seconds -= hours*3600
        float minutes = floor(clock_seconds / 60)
        clock_seconds = floor(clock_seconds - minutes * 60.0)

        c64scr.print("system time in ti$ is ")
        c64flt.print_f(hours)
        c64.CHROUT(':')
        c64flt.print_f(minutes)
        c64.CHROUT(':')
        c64flt.print_f(clock_seconds)
        c64.CHROUT('\n')
    }
}

you get a program that outputs this when loaded on a C-64: