hoosieree / b

It certainly *requires* close study. Not sure if it *rewards* it yet. :)

> note: docs/README.txt is from kparc.com/b/readme.txt

b

I want to understand what’s going on over at kparc.com/b. The docs call it a compiler, but it looks like an interpreter to me. At the very least I can see a REPL in the “main” function[1]. It is implemented in Whitney-style C, an acquired taste.

The readme claims that the generated code is on par with gcc/llvm at highest optimization settings, but with massively shorter compile times, and smaller binaries.

[1]: actually there’s no main, but there is a _start in assembly which invokes the REPL.

download latest

I used wget --recursive --no-parent http://kparc.com/b and then deleted a few spurious index.html?= files.

make/install

No k.c on my machine, so I will only try to make /bin/b.

• MacOS: I failed to get a working build. Lots of “function definition is not allowed here” errors. Seems to have missed a macro somewhere (thinks R is a function definition but it’s really a macro).
• Ubuntu 16.04 vm (VirtualBox): builds b.c with some warnings

overview of files

b.c includes a.h includes c.h

• c.h: typedefs, macros, accessors
• a.h: more accessors, public interface (lots of static inlined functions)
• b.c: entry point (.start instead of main for some reason)

the b executable

“Creature comforts” are absent, looks like a technical proof of concept or development version. Don’t expect training wheels.

• accepts *.b programs from the command line
• does not permit spaces (repl exits)
• no error handling (segfault)
• function definitions work f[ii]{x+y}
• function call works f[2;3] returns 5
• / and \ do not seem to perform left or right shifts as hinted in the documentation (not sure what they do)

impresions

Weird. Feels like C and K at the same time. An “evolutionary missing link” between the two.

related work

A couple others have started on this same journey.

• https://github.com/tlack/b-decoded Has a README and some inline comments in the code. Much further along than me.
• https://github.com/zgrep/b

questions

• What is b?
• Is it a compiler or a REPL (or both)?
• Why make /bin/b which requires sudo? More obvious workflow perhaps? (/bin/ is already on PATH)