19 Feb
2022
19 Feb
'22
10:06 p.m.
https://research.swtch.com/shmacro
On Feb 19, 2022, at 7:44 AM, Will Senn
<will.senn(a)gmail.com> wrote:
I have been poring through the v7 source code lately, and came across an oddity I would
like to know more about. Specifically, in sh. The code for sh is c, but it makes extensive
use of of macros, for example:
/usr/src/cmd/sh/word.c
...
WHILE (c=nextc(0), space(c)) DONE
...
The macros for sh are defined in mac.h:
/usr/src/cmd/sh/mac.h
...
#define BEGIN {
#define END }
#define SWITCH switch(
#define IN ){
#define ENDSW }
#define FOR for(
#define WHILE while(
#define DO ){
#define OD ;}
#define REP do{
#define PER }while(
#define DONE );
...
I can read the resultant code through the lens of my experience coding c, but I'm
curious why the macros and how this came about? In v6, the sh source is straight up c. Is
there a story behind it worth knowing?
Thanks,
Will