Well, yesterday I implemented the “#include” capability. It was actually very fun and instructive - it made me recall the “prepare to throw one away” phrase from “Mythical man month”. Let me elaborate:

I had a gut feeling that there should be some simple, “enlightened” recursive solution for “#include”, but nothing came to my head. So I intentionally started coding a prototype. It resulted in 2 functions, with quite a lot of duplicated code, but it worked. Using the experience from this prototype, I coded a single function, that was shorter than each of the previous ones and did all the job, in that “enlightened recursive” kind of way. Nice ! Indeed, sometimes it’s best to code a working prototype to understand how things work. Note taken.

Then I started implementing the “#define…#ifdef…” family. Oh goodness… this is complicated, and I see no “enlightened” way to code it. I didn’t finish, will take on it now again, hopefully I’ll be over this until the evening. Here comes some rant:

Sometimes, it’s just impossible to create a simple solution to something. The specs are so complicated with so many special cases and things that should go this and that way… I’m willing to challenge anyone, to code a CLEAN implementation of the #define…#ifdef…#else, etc. capability of the c-preprocessor. CLEAN means without tons of flags, and generally code that “looks right” rather than “tailored to somehow solve the problem”.

I don’t feel too bad about it though. It’s because I’ve seen (and even modified) the code of two other, popular implementations of cpp:

• One from Decus, that ran on many IBM platforms: ugly spaghetti, written in old, K&R style C. Dozens of “goto”s and “break flags”. Files named cpp1.c, cpp2.c … cpp6.c (hail modularity !).
• Another from GNU itself. The cpp of gcc 2.96. To say it’s much better than the one from Decus is a big lie. They implement a lame parser of C, with highly unstructured code, huge “switches” with a lot of flags.

Also, people can sing praises to OOP, functional-programming and stuff like that, but nothing will help here. No implementation of this can be really clean, which is very unfortunate

Enough rant for today, back to work…

Related posts:

1. coding a simplified cpp

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