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Rewrite the intro blurb in the README.

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Chris Pressey 2018-09-05 21:36:18 +01:00
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README.md
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@ -3,30 +3,36 @@ SixtyPical
_Version 0.17. Work-in-progress, everything is subject to change._
**SixtyPical** is a 6502-like programming language with advanced
static analysis.
**SixtyPical** is a low-level programming language with advanced
static analysis. Many of its primitive instructions resemble
those of the 6502 CPU — in fact it is intended to be compiled to
6502 machine code — but along with these are constructs which
ease structuring and analysizing the code.
"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.
SixtyPical aims to fill this niche:
"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.
* You'd use assembly, but you don't want to spend hours
debugging (say) a memory overrun that happened because of a
ridiculous silly error.
* You'd use C, but you don't want the overhead of compiler-added
code to manage the stack and registers.
In practice, this means it catches things like
SixtyPical gives the programmer a coding regimen on par with assembly
language in terms of size and hands-on-ness, but also able to catch
many ridiculous silly errors at compile time, such as
* you forgot to clear carry before adding something to the accumulator
* a subroutine that you call trashes a register you thought was preserved
* a subroutine that you called trashes a register you thought it 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
Many of these checks are done with _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.
SixtyPical 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
@ -35,8 +41,15 @@ machine-language programming idioms, such as
* explicit tail calls
* indirect subroutine calls
The reference implementation can analyze and compile SixtyPical programs to
6502 machine code.
SixtyPical is defined by a specification document, a set of test cases,
and a reference implementation written in Python 2. The reference
implementation can analyze and compile SixtyPical programs to 6502 machine code,
which can be run on several 6502-based 8-bit architectures:
* Commodore 64
* Commodore VIC-20
* Atari 2600 VCS
* Apple II
Quick Start
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