suetanvil / lst3r

[MOVED TO CODEBERG.ORG] A (somewhat) refactored and modernized fork of Little Smalltalk 3

Little Smalltalk (Refactored) 3.1

This is a fork of Timothy Budd's Little Smalltalk version 3 with the goal of modernizing the C code and making it more readable and idiomatic. At the same time, I have made every effort to keep the memory footprint small for the benefit of anyone who wants to try to port it to a sufficiently powerful embedded device.

The companion book to this program, A Little Smalltalk, can be downloaded from here.

There is also a manual included with the source tree.

Changes

1. The source code has been broken into modules with public interfaces and hidden private parts. (I.e. for each source file foo.c, there is a header foo.h which declares its public interface; anything using a part of foo.c does so by #includeing foo.h.)

2. Most global variables have been eliminated or made static (i.e. local to their source files only). In addition, many static variables have been eliminated or made local.

3. Function declarations have been converted from the old K&R style to the new (ca. 1990) ANSI style. In addition, the source code has been re-indented to one of the popular styles and tabs converted to spaces in both the C and Smalltalk code.

4. The implicit assumption of a 16-bit int type as (hopefully) been fixed.

5. The header common.h is now the central point for including headers into the entire codebase. This includes env.h, which now contains (I hope) all of the platform-specific configuration, types.h for common data types and util.h for short common functions.

6. Eliminated most macros, replacing the function-like ones with inline functions and the constant-like ones with enums or const variables. The few that are left are either useful as macros or too difficult to remove.

7. Made names of things more idiomatic for C and in some cases renamed things to something more understandable.

8. Removed a bunch of trailing spaces from the command prompt, mostly to play nice with rlwrap.

9. Added the -e argument to lst. This takes one string as an argument and evaluates it as soon as the VM starts up.

10. Rewrote the Makefile to properly do dependencies and to run the unit tests when invoked with the test target. (It also now requires GNU make and a compiler that implements gcc's -MM flag--sorry about that.)

11. Simplified memory management. Ripped out all of the clever stuff and replaced it with calloc and free, since those have many more engineer-years of work in them than anything in the VM code. Also made the post-load garbage collector a bit smarter.

12. Memory reference counts can no longer wrap; if they reach their maximum, the are simply never decremented. (Saving and reloading the image will garbage-collect such "stuck" objects, though.)

13. Will now exit immediately in the unlikely case that malloc fails.

14. When building the initial image, now also creates a file called object-map.txt which contains a textual description of the image. The function that does this (printObjectTable()) can also be called from the debugger. These dumps are invaluable for tracking down image corruption bugs.

15. I/O function calls replaced with ones not (as) vulnerable to buffer overflow.

16. Removed all uses of the keyword register.

17. Added a bunch of assertions of type and memory sanity.

Stuff Remaining

1. The main interpreter function (execute()) is a huge, incomprehensible ball of code that should be refactored into something more readable without a loss of performance on modern hardware and compilers.

2. Many primitives do not adequately check the type and value of their arguments to ensure memory safety (e.g. 42 basicAt: 5). Some of the more egregious cases are now protected by assertions but these holes need to be closed and there needs to be a way to gracefully report the error back to the user.

3. Should switch to the standard := operator for assignments instead of (or in addition to) the <- operator.

4. MS-Windows support. This is strictly a Unix program. Fortunately the code doesn't any exotic API calls so a standard C library should be sufficient to build it as a Windows console app.

5. Probably lots of other things.

This is not a particularly useful Smalltalk implementation--if you want one of those, try Squeak, Pharo or (if you can deal with proprietary software) Cincom Smalltalk. However, it's very small and very simple, so it could be the starting point for some other interesting project.