Comment by silasdb

6 years ago

The whole program trusts definitions in mac.h [1] like:

    #define IF if(
    #define THEN ){
    #define ELSE } else {
    #define ELIF } else if (
    #define FI ;}

    #define BEGIN {
    #define END }
    #define SWITCH switch(
    #define IN ){
    #define ENDSW }
    #define FOR for(
    #define WHILE while(
    ...

Isn't it nowadays considered bad practice? After taking a glance at the code, I see there might be some advantages like not forgetting to add missing {}. Is there any other explanation on why they created a dialect on the top of C using the preprocessor?

[1] https://www.tuhs.org/cgi-bin/utree.pl?file=V7/usr/src/cmd/sh...

EDIT: fix English

3 comments

silasdb

kick 6 years ago

Bourne liked ALGOL. A lot. So much that he was one of the few people who wrote their own ALGOL-68 compiler. Using the preprocessor to feel more at home is a pretty good idea in this case.

This wasn't particularly popular to anyone who wasn't, well, Bourne, even at the time. I posted an example here: https://news.ycombinator.com/item?id=22199664

swiley 6 years ago

I’m under the impression that building up high level languages using macros was very common among assembly programmers, since C was new whoever wrote this may have come from assembly and taken the habit with them.

wgml 6 years ago

The author worked on ALGOL 68C and probably intended to reuse the more familiar syntax.

Nowadays, I would indeed consider it a bad practice to use such macros. Especially if you intend to share the project with anyone else.